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Hi All, First post so be gentle!
Would it be possible to create some sort of location based task alert manager by Cell location? This struck me as useful for example when you might need to do something on the way home from work ("you forgot to pick up the dry cleaning again!"), where you may not know exactly what time you need to be reminded, but by rough location instead. Would something like this be useful to the xda-developers population? I am no coder myself, but cannot imagine this would be overly complex compared to some other apps to come out of XDA dev?
Of all the newbie stuff.. this is probably the best newbie stuff I've heard. It is a good idea.. and it is certainly do-able (there are similar application what switch to different profile based on tower ID). Just need someone to pick up the project.
Seems like all my best ideas are coined in the shower - see I got home today and had once again forgoten to buy shampoo on the way home
bdavbdav said:
Hi All, First post so be gentle!
Would it be possible to create some sort of location based task alert manager by Cell location? This struck me as useful for example when you might need to do something on the way home from work ("you forgot to pick up the dry cleaning again!"), where you may not know exactly what time you need to be reminded, but by rough location instead. Would something like this be useful to the xda-developers population? I am no coder myself, but cannot imagine this would be overly complex compared to some other apps to come out of XDA dev?
Click to expand...
Click to collapse
There is location based profile switch mort script floating around this forum. Try to contact the author. Your idea seems to be quite useful.
hmm, nice idea indeed, this is simple enough to be scriptable (for basic purposes, nothing much fancy)...mortscript is easy enough to do this (just check the value of a registry entry that has the tower string, and then read the msg off a database/text file and alert the user accordingly)..
mm, nice idea indeed, this is simple enough to be scriptable (for basic purposes, nothing much fancy)...mortscript is easy enough to do this (just check the value of a registry entry that has the tower string, and then read the msg off a database/text file and alert the user accordingly)..
Click to expand...
Click to collapse
Would it be possible to have a script such as this one index a bunch of tasks (to pull a tower ID out of the note/location for example) from the default task list?
If by "default task list" you mean the WM/outlook tasks database then I'm not sure. I have never done that. Will look for it.
I'm developing an organizer app as my bc. thesis and I don't have any real Android developer to consult, so I made this thread and hope somebody will help me and point me in the right direction.
I just started to work on it and I have roughly 1 month to make something useable out of it.
So... the first thing that comes to my mind right now is synchronization.
1. I don't know if I should implement it or not.
I have a hosting with 1.5 GB space, a relatively fast connection. Would syncing data (text (probably xml) only) with this server slow it down significantly ? How many users could an average server take ?
And another one regarding sync:
2. I'd like my application to exchange data with my server under the google account on which the device is logged in, so no registration will be neccessary (I suppose the majority of devices are loggen in with google). I'll probably need to get the user's google account name on every sync session. Is that possible ?
The app will already have a server-side app to edit your events and stuff, so I'll need the user's login information again to retrieve his data from my database, but I won't have his password, so I can't make a usual login form. I guess Google has some API to figure out if a user is logged in, doesn't it ?
Any advice will be appreciated.
Can I open a menu with a simple button click ? Like a context menu but for short clicks.
// I solved the **** outta this one.
Still waiting for answers on the first post.
"Organizer App" really doesn't tell us what you're trying to do. It's hard to answer questions if one doesn't know that basic plan of the project you're trying to create.
Check this -> Basic info about my bc thesis
Nice web page...ambitious project for a 4 week time frame.
As a programmer, you know to start small and add functionality as your program grows.
I would start by making a simple"To Do" list: Add item, Delete item, Edit item, Mark item done, Save this list, Recall a list, Delete a list.
Post back when that's done
Rootstonian said:
Nice web page...ambitious project for a 4 week time frame.
As a programmer, you know to start small and add functionality as your program grows.
I would start by making a simple"To Do" list: Add item, Delete item, Edit item, Mark item done, Save this list, Recall a list, Delete a list.
Post back when that's done
Click to expand...
Click to collapse
Agreed 100%.
@ OP:
I don't know much about syncing, but it won't have a large cost of the server's resources - syncing an CSV or XML file is pretty trivial. Even if you have a low bandwidth cap, text files are quite small. So you should be fine in terms of that.
Nobody can give you a "set number" - ie. the server can take "X people." It greatly depends on the server type, how much bandwidth is allocated to you, your traffic priority, etc. I mean if it's one server with like a xeon processor then it can probably handled a pretty heavy load (say 50 probably? (and yes, I'm kind of pulling that number out of my ass)). Though most web hosts don't just dedicate one server to each customer. Typically, now-a-days, everything is virtualized. Everything is unified using server farms (ie. multiple servers or computers) virtually, then virtual chunks of resources are distributed to clients. So even if somebody could give you exact numbers (which is impossible), they'd most likely be wrong. That is unless you paid extra to have a particular server or particular number of servers dedicated to you...but even then, there's a high chance that it's just a chunk of a virtual server farm.
He's right, this is pretty ambitious in a 4 week period, especially if you have other activities going on as well. It's even more ambitious if this is your first app. You may want to reconsider your objectives given your time frame.
As for the google login, you'd need to look at the google API, and see if there's a way to verify peoples' usernames and passwords. If you can, then it's just a matter of encrypting them and storing them in a properties file or something.
Hope that helps ya out some.
Rootstonian said:
Nice web page
Click to expand...
Click to collapse
Thank you
I know, I know. I could have started 4 months ago. But I didn't, the lazy bastard I am.
This is the practical part of my bc thesis. The ultimate deadline is 3rd of june, but I have to have my theoretical part (30-50 pages of text, if IIRC) done by then, all printed out and ****. So I plan to work as hard as I can on this till the end of this month and then start to work on both at the same time. I really don't have any other duties in school, since I have a nice reserve of credits so this is my priority #1.
The main objective is geo-tasks, since that's what the name of my thesis says. Everything else is just an addition (i.e. the widget, that was just an idea, I doubt I will have time for that). So I'd rather start with that (I know, It's the hardest part). Or do you still think I should start with the to-do's ?
You can check out my last night's post to see what I've been up to the last 2 days and what I'll be up to next.
What is your level of Android programming experience (None, Basic, Intermediate, Advanced)?
And I'm a little fuzzy on the whole "Geo" thing. Is it like I have a list "Get milk, bread eggs", "Pick-up dry cleaning", "Get oil change" and then your app is going to "sense" when I'm by the grocery, dry cleaner's and oil change place? Which grocery? I use 4 different stores. Same dry cleaner and oil change though usually.
If so, you are going to need to code in lat/long coordinates for these places and then compute your location vs one of the merchants, compare that merchant to an "active" TO DO list item and pop-up an alert of some sort if you're within a mile. Wow
Your project, you know your skill level. Start where you want I guess LOL.
I think it's more of an agenda type thing - that syncs.
@Rootstonian
I'd say basic, but quickly crawling up to intermediate.
It's almost like you said, but there's only one location for every task. Maybe in a later version...
Well, good luck. Keep us posted
Will do. Hope you guys will keep on helping me
I need to use my database object in more than one activity. How do I pass it from one activity to another ?
Should I create a new instance in each activity ? Or should I create a content provider ? (I'd rather not - they're quite complicated for me and I only need to access the DB in this app).
I'm going to assume you are using a database helper type class.
No need to pass data from Activity to Activity; just open, use and close the database in each Activity as required.
I have a problem.
I created a LinearLayout for all the tasks in the database. Now I want to register all of them for a context menu. I can do that, but I can't figure out which one's menu was triggered.
LinearLayout has a setId method, but it only takes integer values, which is no good for me, because I have 3 types of tasks and if I assign them their id from the database, then the same ID will probably be assigned to 3 different views.
I could use some sort of multiplication, like for timed tasks I would multiply the ID by 10 000, but that's not elegant at all, and it would crash after a few months of using the app.
So what do I do now ?
I'll paste some code.
Code:
public void drawTasks() {
TextView emptyText = (TextView) findViewById(R.id.empty_todo);
if (tasks.isEmpty()) {
emptyText.setVisibility(View.VISIBLE);
} else {
emptyText.setVisibility(View.GONE);
Iterator<Task> it = tasks.iterator();
//create views
while (it.hasNext()) {
//create a temporary object
Task tmpTask = it.next();
//get it's properties
long id = tmpTask.getId();
String title = tmpTask.getTitle();
String description = tmpTask.getDescription();
int important = tmpTask.getImportant();
int finished = tmpTask.getFinished();
//create new LinearLayout for this task
LinearLayout newTaskLayout = new LinearLayout(this);
newTaskLayout.setId((int)id);
newTaskLayout.setOrientation(LinearLayout.VERTICAL);
newTaskLayout.setPadding(5, 0, 0, 10);
taskLayouts.add(newTaskLayout);
//create new views for these properties :
//title
TextView newTaskTitle = new TextView(this);
newTaskTitle.setText(title);
newTaskTitle.setTypeface(null, Typeface.BOLD);
//important tasks are highlighted
if (important == 1)
newTaskTitle.setTextColor(Color.RED);
//finished tasks are italic
if (finished == 1)
newTaskTitle.setTypeface(null, Typeface.ITALIC);
//description
TextView newTaskDescription = new TextView(this);
newTaskDescription.setText(description);
if (finished == 1)
newTaskDescription.setTypeface(null, Typeface.ITALIC);
//add views to this tasks' LinearLayout
newTaskLayout.addView(newTaskTitle);
newTaskLayout.addView(newTaskDescription);
//add new linearLayout to tasksRootLayout
tasksRootLayout.addView(newTaskLayout);
}
}
}
This is self-explanatory. taskLayouts is an ArrayList of LinearLayouts where I keep the pointers to all layouts that need to have a context menu.
There are 2 other similar methods: drawTimedTasks() and drawGeoTasks() which do basically the same (I couldn't figure out a way to do it with one universal function).
Here's how I register them for context menu:
Code:
private void registerViewsForContextMenu() {
//register control bar buttons
registerForContextMenu(newGeoTaskButton);
registerForContextMenu(newTaskButton);
Iterator<LinearLayout> it = taskLayouts.iterator();
while (it.hasNext()) {
registerForContextMenu(it.next());
}
}
And here's how I'm checking for context menu trigger:
Code:
public boolean onContextItemSelected(MenuItem item) {
switch (item.getItemId()) {
case ...
return true;
}
...
}
return false;
}
What am I doing wrong ?
Anyone ?
----
I haven't really been following this thread so I don't know all the details of your app, but I'll try to help.
So each task has 3 views for it? Each task is in the db once? I'm a little foggy on how you're storing them and what the correlations are between views, events, and types of event, more specifically the latter.
If you explain that a little more clear, I can try to help a little better.
There are 3 types of tasks : simple, timed, and geo tasks. Each type has its own table in the db, hence it's own IDs. That means, the first geo task, first simple task, and the first timed task ever added have all the same ID = 1. That means if I want to give their views unique IDs, I can't use their IDs from the database.
So I'm trying to figure out a way how to give the view ID's so I can find out which database record they represent.
In an ideal world, I would be able to define a string ID (i.e. geo_1, simple_1, timed_1), but this is not the case. I dunno why... in XML you give your views string IDs, but programatically you can't.
grandioso said:
There are 3 types of tasks : simple, timed, and geo tasks. Each type has its own table in the db, hence it's own IDs. That means, the first geo task, first simple task, and the first timed task ever added have all the same ID = 1. That means if I want to give their views unique IDs, I can't use their IDs from the database.
So I'm trying to figure out a way how to give the view ID's so I can find out which database record they represent.
In an ideal world, I would be able to define a string ID (i.e. geo_1, simple_1, timed_1), but this is not the case. I dunno why... in XML you give your views string IDs, but programatically you can't.
Click to expand...
Click to collapse
If all of the tasks have common elements (even if they don't really), you can merge them into one table. Then define an enum or something for the task type, as a simple field in the table. This removes the issue with duplicate ID's, while still being able to differentiate what type they are. You can typically leave fields blank in a database, so you wouldn't have to worry about what's filled in for tasks that don't have particular fields associated with them, just verify all fields prior to mutating the database.
If you're hellbent on keeping three separate tables you can hold a global ID, which can be an intersection between all three tables. So this wouldn't be the primary key, just a global ID, and you can key them up by that. Not entirely sure where you'd keep it to persist over power cycles unless you just make a 4th table with one row and store it in there. Or just throw it in the program's data somewhere.
The reason you can define things in the XML is he XML is compiled into the R class at compile time...though everything in there *should* have a corresponding methodology to get it done programatically. Though if you're talking about the primary key, as far as I know that is always numerical. So the ideal world may not apply - BUT, that doesn't mean you can't create a field that stores a string id (which I wouldn't, because string comparisons take a lot of time, but whatevs).
Hope that helps you out some, I don't really touch databases and am very new to Android programming, just know what I know from absorbing info from others - but I know a pretty decent amount about programming in general and know Java pretty well so I can probably help you out the best I can in some respects.
During recent development of my app (see my signature) I focused a lot on how to optimize the already working code further in order to make it smoother without loosing quality or using too much memory. Well I came across some mistakes I had made in my early days of developing Android so I figured it might help the beginners and intermediate developers. So here I collected my suggestion of common mistakes and best practices in Android. Let me start by making you familiar with a motto which you might know if you have developed Perl before.
TIMTOWTDI
There's more than one way to do it, in short TIMTOWTDI is a well known aspect of the Perl language, which aims at giving programmers the freedom to choose their way of doing things. It “doesn't try to tell the programmer how to program.” Well it does have various disadvantages such as possibly messy code and barely readable code, but it offers programmers to use their preferred style.
The only reason why I'm bringing this up here is because it helped me a lot to think that way, since TIMTOWTDI sometimes applies to Java as well and a way somebody else is preferring might not be better than your own way. But it is never bad to have a look at how others code the important tasks and sometimes the performance or readability gain is tremendous. So I'm not telling you to exactly use my way, but advice all beginners to perhaps rethink their code .
Tweaking Android Apps
The first step is always to look at what the awesome Android documentation says about performance, so I can more than advise you to read this straightforward article about what to do and not to do on Android. It covers some very important performance issues like the expensive object creation and method invocations. It is crucial to follow those basic rules while trying to develop fast Android apps. I will cover and further explain some of their suggestions here, but will try to also look at them from a developer's perspective who cares about readability and simplicity.
Now onto the code, let's start with some basic Java practices and then move on to some more Android specific styles and improvements.
Looping wisely
Often it doesn't matter if you write slow code and lose 1 or 2 milliseconds but especially in loops and everything that can be called once a frame you suddenly loose a lot of time. Thus it is crucial to especially pay attention to those repeated parts of your code like the onDraw() method in your custom view implementation (see last section) and start optimizing there. Let's take a look at what kinds of loops we have, the slowest first and the fastest ones towards the end:
while
The while loop is probably the first complex programming structure you learned, and just writing
Java:
success = false;
while (!success) {
trySomething();
}
is extremly readable but can potentially run forever or longer than you need it to. One aspect which is often overlooked is that the condition inside the parentheses will be checked on every run of the loop! So even a simple string.length() call can be optimized (if the String won't change) saving its length as an int and then using that in the condition block.
Its unpredictability and lack of possible tweaking done by the JIT makes the while loop a tool that needs caution but is sometimes crucial to complete the task. Just make sure you only use the while loop if there is no way to predict when your condition is false. For almost all other cases, you can do some calculations and use one of the iteration loops:
for (traditional)
This one is widely used like this:
Java:
for (int i=0; i<getSize(); i++) {
doSomethingWithIndex(i);
}
Even though this is more predictable, consider how the program will run: Before every execution of the block, the condition i<getSize() has to be checked, so getSize() is called (and an Android, method calls are expensive!). You could now think, alright, we'll just cache our size upfront like we did with in our while loop, but examine the following fast example of iterating through an array:
Java:
for (int i=getSize()-1; i>=0; i--) {
array[i] = getNewValue(i);
}
The trick is starting at the last value and then iterating backwards until 0 is reached. This may not work at all times, where the order of the blocks may be important or it is redundant due to having a fixed end value, but it saves both method calls and memory usage needed to get the last value before going into the loop.
But that is hardly readable and you often have to rethink because of looping backwards, so we can do better can't we?
for (iterator-based: “foreach”)
Dealing with an array, List or other collection of data you can easily do something for every part in that collection using the foreach loop:
Java:
for (Object item : objects) {
doSomething(item);
}
That is the fastest way you can iterate through any kind of iterable collection because it can be heavily optimized by the compiler and is also simplistic and readable. The only problem here is that you don't have the index of the item you're getting and you can't write data to the collection. To accomplish that one of the slower for loops must be used.
Keywords do matter
This is a minor one that is overlooked often. Beginners in Java mostly don't use keywords and access modifiers like “private”, “public”, or “final”. That is fine since we all love simplistic code don't we? And an honest word, if you don't write a library or work on your code with a big team, you don't have to know much about the access modifiers, but if you want to, there is always the Java documentation. But the “final” identifier is actually pretty important to both the ones reading the code and also the compiler, since it can just insert its value into the references. That means, that whenever you declare an instance variable, think about if it is likely to change or if you can declare it as final. Within methods, making use of the “final” keyword does not really change much for the compiler, but it sometimes helps you make a clearer design so you directly get a compiler warning whenever you're trying to change a final variable's value.
A side note on making “static” variables and fields – I wouldn't recommend that on Android unless you know what you're doing or you're using it together with “final”. A “static final” instance variable is the best way to declare constants in Android because the compiler can replace it fast and ART can replace it during the install of your app!
Strings are special
Let's talk about something that is fundamental to Java – the String object. Well it's not a real object since it is actually immutable. That means a String can only be created or collected by the garbage collector, it can't be changed (which is very important since object creation is god damn expensive in Android so it would make our apps pretty slow)! Wait, then what happens if I call one of the awesome methods in the String class like substring() or replace()? And here comes the downside: These methods have to create new Strings and the old one is collected by the garbage collector. While this might be totally alright if you're just parsing some basic user input, if you need to perform some heavy String operations like many substrings, a whole lot of unused garbage and overhead is created. This doesn't only mean that you are temporarily using a lot of memory, with the garbage collector needed to kick in it also affects your performance.
So how do we get around this problem? Luckily there is a Java class which can do almost the same as the default String implementation, the StringBuilder. This class will hold a char array with all the chars you had in your String. The class can take care of managing that array like initializing it with a default length of 16 and creating a larger array once you have more characters that would fit into it. Take a look at the constructors as well – with new StringBuilder(length) you can directly make that array as long as it needs to be and with new StringBuilder(string) the array is instantly filled with the string. The big advantage the StringBuilder is that it can modify the array instead of having to create new Strings every time. If you're finished with the heavy modifying, just call toString() to get the String back.
If you want to read more about it, here's a nice article.
Android-specific tips
Bundling is better than trundling
Let me explain this with an example: Let's say you are dealing with some data concerning persons so you are saving their name, age and gender. In any object oriented language like Java you would create a wrapper object holding that data:
Java:
public class Person {
private String name;
private int age;
private boolean isMale;
public Person (String name, int age, boolean isMale) {
this.name = name;
this.age = age;
this.isMale = isMale;
}
// additional getters and setters go here.
}
Of course you could do that in Android as well, but you will encounter this problem: What if you need to save your Person array or need to pass a specific Person to another activity? Well, you have a few options available:
You could override the toString() method in Person so it contains all its data and parse your array into a String array manually. Then another constructor will be needed to get the data back from the String using our beloved String operations. But there is still the problem that when you want to add data to the person like height later, you have to reconsider the toString() method and it's constructor counterpart.
Alternatively, wanting to integrate it better into the system, you might want to implement Parcelable in the Person class. That way you can directly put person extras to your Intent or save it to SharedPreferences. But that seems like more work if you want only a simple container for your data. Once you need have a more complex class it might be advisable to make it Parcelable (perhaps using the Android Studio plugin, thanks @nikwen), but let's start with an easier apporach here.
This is how I do it: I use a Bundle instead of a person class to store all the needed data. The Bundle class already implements Parcelable and and simplifies adding data for you. What is more, you are probably already familiar with it since you get one calling getExtras() on the starting Intent of your activity! Now back to the example, this is how it would be done:
To not get confused about all the keys you need, let's create a class containing some static final keys:
Java:
public class Person {
public static final String NAME = “person_name”; // will contain a String
public static final String AGE = “person_age”; // will contain an int
public static final String ISMALE = “person_ismale”; // will contain a boolean
}
While this is only needed for consistent keys, here is how you would create the Person:
Java:
public Bundle getPerson(String name, int age, boolean isMale) {
Bundle person = new Bundle();
person.putString(Person.NAME, name);
person.putInt(Person.AGE, age);
person.putBoolean(Person.ISMALE, isMale);
return person;
}
Similarly, you can get one or more stored values of the Bundle using one of the person.get...() methods. Furthermore, instead of creating an array of Persons you can now create a Bundle of persons using bundle.putBundle()! You just need to find the right key-scheme, here you could either provide an id for each person or just use their names as key (although the key array has to be passed seperately). And what do we get from all this? Well we can now just call intent.putBundleExtra(person) and voilà, we've passed it to another app component.
Resourcing is not outsourcing
One of Android's big advantages is its exceptional resource system. The fact that all your Strings and values are saved in a separate xml file makes your app not only easier to translate, but also keeps your code cleaner and lets you have a complete overview of what amount of constants you use. But you can go further than that. The resources allow for entirely different configurations depending on screen size, resolution, orientation, location and api-level! To learn more about how this can be done, head over to the Android devoper guides.
One thing I wanted to highlight is that it used to be quite hard to make a consistent interface and still support Android 2.1 and above. That is not the case any more since we now the the continuously improving AppCompat library. It is even useful for apps targeting only ICS and above because it contains bugfixes and improvements for those versions as well. Using this library is the best way to get the holo theme and its ActionBar in your app, although if you could also try ActionBarSherlock to accomplish the latter.
Click to expand...
Click to collapse
Think D.I.P
So what's this strange thing they call dip? And why do we even bother using it, we have had pixels (pix) since the beginning of programming. First things first, try to avoid pixels on Android. On almost every other platform using the smallest unit that's available is a great thing in layouts, but not so much on Android where apps can run on devices as small as a smartwatch up to 2k tablets. The problem is that you can't be sure if a single pixel is as small it can barely be seen or as large as a few millimeters. That is why we have the standard-sized density-independent-pixels (dip or dp in short) where 48 dips are roughly equivalent to 9mm, the convenient size of a touchable area (e.g. a Button). Great, then how many dips is my screen wide/high? That is not an easy question since it varies as well. Phones usually have around 320dips (at the smallest width) but larger screens can fit more so on tablets you have 600dips or more. Try to understand this documentation and don't be confused with the abbreviations dp, dip and DPI – dp and dip are the same and DPI is dots per inch (similar to pixels per inch), the screen density!
The reason why I'm bringing this up here is advice you to understand and always think in dips, never in pixels. Even on a Canvas, where there is only methods for pixels, don't think “ok I draw my text 20 pixels from the left edge and 50 from the top so canvas.drawText(“text”, 20, 50, myPaint);”. Start to think in dips: “I have to draw it 16dip from the left edge and 24dip from the top!” But how to convert it to pixels so it can be actually drawn onto the Canvas? It really is a shame there is no method in the Context class to directly convert dip to pixels, so here's the one I use:
Java:
private DisplayMetrics displayMetrics;
/**
* Converts a given dip (density independent pixel) value to its corresponding pixel value.
* @param dips The dip value to convert, as float.
* @return The pixel value, as int.
*/
private int dipToPix(float dips) {
if(displayMetrics == null)
displayMetrics = getResources().getDisplayMetrics();
return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dips, displayMetrics);
}
And a side note on sp, that is the scale-independent text size. Try to use it as far as you can, for instance in layout resources. But just in case of needing the actual size, use the same method because sp is computed almost the same as dip.
Hyperthreading is not that complex
An app's UI (or “main”) thread is its beating heart, and we don't want to slow down what's powering us if there are other options available, right? If you don't follow the rule of not performing any time consuming tasks in the default thread you'll end up with what all developers fear: The “App is Not Responding” dialog – in short ANR. When users see this, they can get really mad, from just force closing your app and uninstalls to 1-star ratings everything is to be expected. Because it is crucial to know about Threads (and Processes), carefully read the guide in the Android docs about it, pay special attention to the two simple rules in Android threading:
1. Do not block the UI thread
2. Do not access the Android UI toolkit from outside the UI thread
Click to expand...
Click to collapse
Let's take a look at the first one, what are you going to do instead if you need to accomplish an expensive task like web requests, complex calculations, Bitmap operations, database queries and I/O management?
Well the answer is not as simple as it may seem since it depends on what and how often you will be doing that task. A task that is performed once per activity launch is almost always wrapped into an AsyncTask, a class which is heavily optimized and integrated into the system. If you know how it works it is a very powerful tool since it does most of the heavy lifting for you, so let me show you how to do it:
You start by extending the AsyncTask class like so:
Java:
private class MyAsyncTask extends AsyncTask<Param, Progress, Result> { //...
Usual stuff, except for the weird <Param, Progress, Result> thing. It is actually not that hard, these are all just type declarations of variables your methods want to use. Thus, the first one is the type of starting parameter you want. Think of it as if you wrote your task in a separate method without access to any instance variables, what data would it need to work (what params would you pass to it in the parentheses). The second one is actually often unused and is needed if you want to return a var indicating progress on the task so it can be published e.g. in a ProgressBar. Lastly, Result is (you may have guessed it) the type of variable you want your task to return, to be published in the UI as well. A typical configuration would be <Uri, Integer, String> for a task reading a file. Note that these have to be objects, so for primitives you'd have to use their respective Java classes like Integer or Double. But that also means that a Bundle can be used as well so we know how to pass multiple parameters now! And there is another way as well, look at the overridden methods:
Java:
protected Long doInBackground(Uri... uris) {
// do your expensive work here, it runs on a separate thread!
}
protected void onProgressUpdate(Integer... progress) {
}
You'll notice the three dots after Uri and Integer. To keep it simple, treat it as an array, so to access your value call uris[0] and progress[0], respectively. The reason for it being an array is that you can start the same AsyncTask with multiple parameters of the same task:
Java:
new MyAsyncTask().execute(uri1, uri2, uri3, uri4);
This is extremely useful in this case to read multiple files at the same time (don't be confused with the configuration in <> above, the param(s) passed to execute() are joined together in the Param array).
A side note on progress here, if you want to publish progress during your doInBackground(), just call publishProgress(Progress) and override onProgressUpdate() to publish the changes in the UI. Similarly with onPostExecute(), you'll probably want to override that method as well to show your awesome result to the user.
What you need to keep in mind is how AsyncTask is handled internally, read the section “The 4 steps” in the AsyncTask documentation carefully. In fact, doInBackground() is method you need to think about the most since it is encapsulated in a separate thread with no access to the UI or methods in your activity.
Because AsyncTask is limited to one operation and should only run up to a few seconds, there are a couple of other ways to do tasks in the background like a second Thread and helpers such as Handlers. The Handlers are needed to access the UI from the worker threads, still following the second rule above. If you want to read more here's an awesome Vogella tutorial about it.
Fragment-tation
This next one is really a good style of development and can save a lot of work if you provide layouts for both phones and tablets (which you definitely should). The basic theme of using Fragments is to follow the divide and conquer technique, which dates back to ancient time in Babylonia. Thus, the idea is to have one large problem (a user interface and its data for both tablets and smartphones) and split it into multiple simpler ones (in this case having one or more Fragments for each screen on phones). Especially in multi-pane layouts, for instance in the settings app, Fragments are a wonderful tool to avoid the use of two different activities, one for phones and one for tablets. The steps to implement them in your app are pretty simple and there are already some neat guides like the one in the documentation and Vogella's one. An additional use-case for Fragments is to retain an AsyncTask when rotating the screen. You would create a Fragment without layout in the UI and call setRetainInstance() on it. Any expensive AsyncTask can then be started inside that Fragment and is not stopped when the activity is recreated during an orientation change.
Memory-zing is unneeded
But it is not only performance, layout and style which can be improved, think about memory usage for a second. It goes hand in hand with performance since an app which consumes unnecessary memory (garbage) will be slowed down by the garbage collector (GC) thrown in from the system, trying heavily to free some RAM. On Android this is extremely important, since a garbage collector running intensely on a single or dual core processor can really slow down the device's performance. That is also why method calls and object creation are so expensive and have to be used with caution – the overhead they produce bumps up the memory usage. And there is one specific case where you can really have a problem with your memory, a so-called memory leak. What this means is that some part of your app is holding on to a very large object like a Resources or database one or even a whole Activity or Fragment. The problem is that the GC can only collect objects which aren't referenced from an active part of your app so this means it can't be collected and ends up blocking all your available memory. Such a leak is something you want to avoid at all times and there are some awesome tools to find out if you have one. All you need to know about that and memory optimizations in general is covered in this amazing I/O talk, so I advice you to watch that!
Most of the time there is no real need for reducing method calls and object creation because the GC is fast enough. But there is one step where it is crucial to avoid it, methods which are called on every redraw like the onDraw() method of a View, which I'll cover in the following.
Optimizing performance? onDraw!
In your custom views the most important method to think about is the onDraw() method since that is where everything that is visible to the user is rendered. A lot can be gained (or lost) in that crucial step, so try to follow the performance guidelines posted earlier as close as possible. Especially, pay attention to the object creation, creating a few objects in onDraw() might not seem expensive, but the memory footprint and the garbage collector usage will be tremendous. When drawing on a Canvas for instance, a common pattern would be to check if the paint instance variable is null before drawing:
Java:
if(paint == null) {
paint = new Paint();
paint.setColor(drawingColor); // ...
}
That code would typically be placed in the surfaceCreated(), but could also be in the onDraw() if you are lazy and want to keep it in one place. . While object creation is not the only thing you can improve performance-wise, just try to apply the aspects I wrote about in the beginning, especially those loops!
One thing I have to point out about performance before moving on to some links that might help you is that before trying to optimize your app in some arbitrary way (and totally destroying readability) measure upfront. That means use the tools mentioned in this great I/O talk covering graphics and performance to get a sense whether your app is really driving close to that 16 millisecond threshold to get the desired 60 frames. Additionally, it might be a good idea to not only test it on the high end devices (#Nexus5) but also those with a high “resolution/processing” value such as the first tablets with 1080p resolution. Thus, only start tweaking performance if you know you take too much time, then try to nail down the time consuming methods. And always try to improve readability and simplicity, not only for us when posting pieces of your code here but also for yourself: it helps getting into the flow if you see that your code is readable and nice .
Additional resources
If you can spare some time and want to know more about how to build awesome apps and UIs, check out the Android sessions at Google I/O 13, especially the Android UI design talk and the Android Protips 3 (but the first and second Protips were great as well as the beginner's talk from 2010). There is also the Android developers blog and the Vogella tutorials. As usual, the Android developers page is always a great resource and Google is still your friend (use “android dev” together with your question to get better results). For more info about general Java performance improvements, I found this nice pdf outlining how you can improve your code even further.
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</guide>
Anyway, that's about it. It has really become a way too long collection of links and videos so I hope it was useful and perhaps made you rethink your code . If you've got any comments or suggestions feel free to post them here, helps a lot.
This guide was featured on the portal on February 4th (thanks eagleeyetom!)
To be continued...
One Thanks isn't enough!
Great writeup! Thanks!
Wow man such a good information muchly appreciated great job!
Sent from my Nexus 4 using Tapatalk
Wow, great collection of tips and tricks. Much appreciated!!
Handy tips
awesome job dude.was really helpful!!!!!:good:
Great article! Please keep going. :good:
Simply awesome...great work.
Sent from my SAMSUNG-SGH-T989 using Tapatalk
Thanks for this great writeup! The android specific tips are really interesting.
Great guide (again). :good:
Just one thing I want to add: I still prefer wrapper classes which implement Parcelable. In fact, it's not that difficult and you should be able to do it in a few minutes. Have a look at the example code here: http://developer.android.com/reference/android/os/Parcelable.html That's it.
I've also found an IntelliJ plugin for that purpose (but I haven't tried it yet): https://github.com/mcharmas/android-parcelable-intellij-plugin
That wasn't meant to degrade your work though. It's an amazing guide.
nikwen said:
Great guide (again). :good:
Just one thing I want to add: I still prefer wrapper classes which implement Parcelable. In fact, it's not that difficult and you should be able to do it in a few minutes. Have a look at the example code here: http://developer.android.com/reference/android/os/Parcelable.html That's it.
I've also found an IntelliJ plugin for that purpose (but I haven't tried it yet): https://github.com/mcharmas/android-parcelable-intellij-plugin
That wasn't meant to degrade your work though. It's an amazing guide.
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Good point and thanks!
Having a closer look at it, implementing Parcelable is not that much work and it would definetely be the more advanced way. Bundle is basically just another layer that makes things a bit easier for the start (and no typecasting) and I found that it can really shine with a singleton class holding the keys and the getters and setters (which have an additional param, the Bundle). For a beginner who just wants to save some values (possibly keeping the keys in the activity or even hardcoded) using the Bundle is a lot easier. Yet again, TIMTOWTDI
Thank you!
Hey Simplicity, after few years there is something you would change? Maybe dagger2, kotlin, rxjava changed the game, as really open question what do you think about?
The question might be a bit off topic, i am working on a root app development but i am pretty confused that how should i get the busbox commands to run on button press, i have given the path and everything but how am i supposed to create a busbox file in data/data/package/files.
This part is confusing me I am not able to create that file, should i keep it in res while creating the app ? And also one last question, from where can i get that busbox file with all its command. Please help, I'm sorry if this is the wrong forum I'm new to posting questions and also to app development .
The harvard university android app from google play store. (I can't seem to post any outside link yet for this account)
I want to create one for may school but I'm just starting to learn android programming, so guys I need your help on the topics that I need to study to create an app like that. I greatly appreciate any kind of comments. Cheers!
clonedaccnt said:
The harvard university android app from google play store. (I can't seem to post any outside link yet for this account)
I want to create one for may school but I'm just starting to learn android programming, so guys I need your help on the topics that I need to study to create an app like that. I greatly appreciate any kind of comments. Cheers!
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Click to collapse
Fragments, ListViews, JSON parsing (for communication with the web server to download news etc), Android SQLite databases (I suggest using this to store the information from the webserver locally so the app does not require a constant internet connection to view a news article for example), Google Cloud Messaging notifications, notifications, encryption.
There are lots more but these are some of the main ones. In addition I would not advise trying to copy the "look" or aesthetics of the Harvard application as it frankly looks disgusting, whoever designed that needs a course in UI design
any book suggestions?? im only studying at home and wanted to start studying android app development
m0nm0npalam0n said:
any book suggestions?? im only studying at home and wanted to start studying android app development
Click to expand...
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Android Application Development for Dummies and Learn Java for Android Development are 2 that I have in ebook form, though I can't say I've used them much as I don't really learn by reading books, more like looking at the source code of other apps and messing with it to see what happens
Android Application Development for Dummies goes through a wide range of topics including widgets, SQLite storage, possibly SharedPreferences (can't remember), ListView etc but does assume that you can at least follow what the sample code is doing - the sample code is commented but if you have not done any coding at all before then you probably should learn the basics of Java before reading it
Jonny said:
Android Application Development for Dummies and Learn Java for Android Development are 2 that I have in ebook form, though I can't say I've used them much as I don't really learn by reading books, more like looking at the source code of other apps and messing with it to see what happens
Android Application Development for Dummies goes through a wide range of topics including widgets, SQLite storage, possibly SharedPreferences (can't remember), ListView etc but does assume that you can at least follow what the sample code is doing - the sample code is commented but if you have not done any coding at all before then you probably should learn the basics of Java before reading it
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Click to collapse
thanks man! this really helps
Jonny said:
Fragments, ListViews, JSON parsing (for communication with the web server to download news etc), Android SQLite databases (I suggest using this to store the information from the webserver locally so the app does not require a constant internet connection to view a news article for example), Google Cloud Messaging notifications, notifications, encryption.
There are lots more but these are some of the main ones. In addition I would not advise trying to copy the "look" or aesthetics of the Harvard application as it frankly looks disgusting, whoever designed that needs a course in UI design
Click to expand...
Click to collapse
Thank you very much for the reply, I'm really thankful for the information that you share. Can you please clear this one for me?
I suggest using this to store the information from the webserver locally so the app does not require a constant internet connection to view a news article for example
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clonedaccnt said:
Thank you very much for the reply, I'm really thankful for the information that you share. Can you please clear this one for me?
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When you get data from a server to an Android app you use php for the server code - for example you can use php/mysql to run a search for calendar events in the database and return those events. Then you need to use php's JSON encode function to send the data in a JSON array.
The output should look something like this - this is the output of the calendar database for my school:
http://wgsb.cobainschofield.com/android_db/get_calendar.php (note this is not the live schools site, its the test server the guy who maintains the live site allows me to mess with err use).
You would then use a JSON parser class and an AsyncTask from within the app to "download" the content of the JSON array and then display it in a listview or textview etc.
Now obviously to get this information requires an internet connection yes? So every time someone wanted to check for an event on the calendar or read a news article for example they would need a working internet connection to receive the output of the get_calendar script, this is inefficient and bad design as it does not allow for offline viewing of the data.
Therefore what you can do is use androids SQLite implementation to create a local sql database then the first time you need to get the data from the webserver, you connect to the internet and get the output of the php script, the using the JSON parser class you store the information in the sqlite database then get the information from the database to display to the user.
By this way users can view news articles or calendar events offline and you only need to connect to the internet to refresh the information
I've uploaded screenshots in the attachments of how I've done it for my school's app.
That made it clear! Thank you very much.
I am going to develop an android examination but I can't decide what kind of layout to use, the app will contain different type of questions(randomized), identification, multiple choice, matching, and true-false. Different examination types are commonly organized by category on a paper-based examination. The exam must also have a timer which is available on every view of the app. I want to give the user the functionality to get back on the questions that he/she skipped. How I am going to send the data back to the web server after.
Thank you and God bless!
Guys, I really need some help here.
Relative Layout is a good one always
clonedaccnt said:
I am going to develop an android examination but I can't decide what kind of layout to use, the app will contain different type of questions(randomized), identification, multiple choice, matching, and true-false. Different examination types are commonly organized by category on a paper-based examination. The exam must also have a timer which is available on every view of the app. I want to give the user the functionality to get back on the questions that he/she skipped. How I am going to send the data back to the web server after.
Thank you and God bless!
Click to expand...
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I would go with a RelativeLayout and then for the multiple choice a LinearLayout and maybe a FrameLayout for the going back and forth between questions and what not. Honestly , I would wait to send the info to the web server till the exam is done. So I would set up a timer lets say 30 seconds per question and if they don't answer it in time it automatically moves on and lets say at the end you were able to answer other questions faster and the total time isn't equal too 10 mins then the spare time they have can be used on questions they weren't able to answer in time and once that is done i would submit it to the server this way they don't use battery like crazy.
Relative Layout.
clonedaccnt said:
I am going to develop an android examination but I can't decide what kind of layout to use, the app will contain different type of questions(randomized), identification, multiple choice, matching, and true-false. Different examination types are commonly organized by category on a paper-based examination. The exam must also have a timer which is available on every view of the app. I want to give the user the functionality to get back on the questions that he/she skipped. How I am going to send the data back to the web server after.
Thank you and God bless!
Click to expand...
Click to collapse
A list of questions is perfectly suited for a linear layout (vertical). Inside the linear layout you could use a second linear layout (horizonal) to separate different parts of your question that should go next to each other.
This typically gives you the cleanest view.
Parts that do not fit a linear layout can be put in a relative layout. In most applications you will end up with several nested lay-outs.
Finally, are you designing for phone or tablet? For the latter, you may consider using frames, where you have the questions in one frame and other information (buttons, options, settings, login) in another. This creates a much nicer and cleaner overall application (otherwise your screen is filled with the questions only, which is a waste of good screen space).
Check the layout section on the google developer website (via training). I think this is useful for you.