Hi Guys,
Because the standard API's to use the camera aren't flexible enough I need to use directshow.
Unfortunately I'm not a very good C++ programmer (more C# ;-))
I found this solution. Wich compiles a C++ DLL and can be called from C#.
Perfect! Except the C++ code doesn't really do what I want to. (And I have no idea how to change it)
See attachement for the C++ project
Dll does: Capture one frame from the camera and store it as a file. (with 320x240 resolution, not great quality)
I'd prefer to use the best available quality, or mayby choose the quality I want.
Also I'd prefer not saving/storing the file but return a stream / bitmap / image
Because I only want to show it on screen (actualy let a mobile webserver respond an image with as much frames per sec as possible)
(Saves a step, storing and deleting everytime)
Any Help?
PS. I also tried Directshow.Net Library But it doesn't seem to work on Windows Mobile.
C# Code
Btw, this is the code I use in C# to create the functions:
[DllImport("CameraCaptureDLL.DLL")]
private static extern bool CaptureStill(string Path);
[DllImport("CameraCaptureDLL.DLL")]
private static extern bool InitializeGraph(IntPtr hWnd);
Just to keep y'all posted, I'm now looking @ this solution (CodeProject.com)
They rewrote the DLL file, and I think it's gonna do what I want, but I first need to install Windows CE 5.0 wich takes alot of time....
I met same problem with you.
I just want to show the camera sight, like the Camera app's Preview function.
I don't know if there is a HTC's Camera SDK.
Please keep contract, if I have any improvment, I will tell you.
I had fun with camera but not using directshow or the preview...I'm just launching the camera app (using sample camera in SDK).
If anyone find an easy way to have "embedded camera display" in an application I'm really interested!! (like a pictureBox having camera as image source)
If I found something I'll tell...
DarkAngelFR said:
I had fun with camera but not using directshow or the preview...I'm just launching the camera app (using sample camera in SDK).
If anyone find an easy way to have "embedded camera display" in an application I'm really interested!! (like a pictureBox having camera as image source)
If I found something I'll tell...
Click to expand...
Click to collapse
I found functions and its parameters by sniffig camera calls on my VOX
Captured data is stored as UYVY.
m32
m32 said:
I found functions and its parameters by sniffig camera calls on my VOX
Captured data is stored as UYVY.
m32
Click to expand...
Click to collapse
Could you provide the compiled version of the htccamera dll ?
Will try to build this later (@work don't have cc compiler, just VS2008)
Thanks!
An in-memory capture would almost certainly improve the live-scan mode in Barcorama also! I could really use that in-memory capable CameraCaptureDll.dll.
Many users seem to have successfully compiled the source at http://www.codeproject.com/KB/mobile/samplegrabberfilter-wm6.aspx, but I can't find the compiled dll somewhere .
I fail to compile it myself as it needs the WindowsCE Platform Builder and VS2008...
Anybody that comes across the DLL, please share!
have fun,
hypest
Hello,
working on it ^^ I will upload the dll here later today
Here you go : download (if fails : try here)
is the source code compiled (look in /bin/Release). Tested and works nice (deploy the dll then the sample app).
Hope this helps!
Thanx!!
will try it!
UPDATE:
The sample opens up but seems to do nothing on my kaiser. <-UPDATE: wrong! it works OK.
I have managed to use the DLL directly though. The capturing works fine but the capture-stop seems to fail: the Stop() function hangs. I use the Shutdown() that seems to be OK, but then I have trouble re-initializing the whole procedure. Also, there seem to be a sensitivity on manually using the garbage collector.
Thanks again anyway!!
Cannot seem to import the dll into another project
@DarkAngelFR
Thanks very much for the sample app for video streaming, was very helpful.
However I really need to use the dll or even the import the CameraCaptureDLL c++ code into our project. I have already read over the ReadMe text file but need further help on how to create this object? Have already tried the Ignore Input Library property and that does not work sadly. Any help would be great!
Thanks,
John
m32 said:
I found functions and its parameters by sniffig camera calls on my VOX
Captured data is stored as UYVY.
m32
Click to expand...
Click to collapse
I have build the camerasniffer dll (and called it htccamera.dll) with mingw32ce, but how do I use it?
I tried copying it to "/windows" and rebooted the phone (hermes) but I do not get a log file on the storage card. Any hints?
Thanks a lot!
Hi,
I got this error when I try to debug this application on my mobile (HTC HD2)
"An unhandled exception of type 'System.MissingMethodException' occurred in TestCameraCapture.exe
Additional information: Can't find PInvoke DLL 'CameraCaptureDLL.DLL'."
But it seem to works fine on the Emulator.
How can I test it on my mobile then?
EDIT
Problem solved, I just had to copy the 'CameraCaptureDLL.DLL' file to the folder where the application is running.
does it run java or not?
can someone go on a java applet and tell me what it says?or does?
guess ill have to buy one and see...
will
be posting an update soon
Sorry to kick this one alive.
I was hoping I could run scottrades live ticker aplet on here. No luck so far.
Anyone know a way to run java aplet?
Thanks
Yeah it doesn't support a java applets. Test it on my friends. I wonder if honeycomb supports it?
Sent from my HTC HD2 using XDA App
Investigated this myself -- despite android have 'some java' built in (i.e. dalvik VM) it does't have a VM capable of running a java applet.
One of the big missing things in Dalvik is the class libraries that are part of a normal JVM/JRE/JDK. In particular, it doesn't have awt, and/or swing (class libs used for UI type stuff).
So applets -- nope. Sometime? Maybe ... I think the OpenJDK guys have all the needed class libs making it JDK compatible but not having any proprietary encumberances. Maybe using this, there is a snowball's chance in hell that some enterprising organization or person, could attempt to cobble in some sort of support for more vanilla java stuff; maybe even including applets.
anybody have any other info on this?
fwelland said:
Investigated this myself -- despite android have 'some java' built in (i.e. dalvik VM) it does't have a VM capable of running a java applet.
One of the big missing things in Dalvik is the class libraries that are part of a normal JVM/JRE/JDK. In particular, it doesn't have awt, and/or swing (class libs used for UI type stuff).
So applets -- nope. Sometime? Maybe ... I think the OpenJDK guys have all the needed class libs making it JDK compatible but not having any proprietary encumberances. Maybe using this, there is a snowball's chance in hell that some enterprising organization or person, could attempt to cobble in some sort of support for more vanilla java stuff; maybe even including applets.
anybody have any other info on this?
Click to expand...
Click to collapse
Let us know thanks.
fwelland said:
anybody have any other info on this?
Click to expand...
Click to collapse
There is Java SE embedded for ARM which should provide JavaSE with all standard libs such as awt and swing.
Don't know if this runs on the Galaxy Tab though, did not try for myself.
it seems like I can create an Activity thus:
Code:
public class MainActivity extends Activity
and then create other activities like this:
Code:
public class SplashActivity extends MainActivity
and the SplashActivity should inherit the "extend Activity".
Fine.
But what is the point in this? It seems that even if I extend a master java file I still don't get any of the other imports inherited, like os.Bundle.
If I could inherit all the imports from a master java file I'd understand extending the MainActivity.
Can anyone shed light on this?
extends has absolutely nothing to do with imports. It allows the subclass to inherit public and protected methods and variables of the superclass and also allows you to override the methods if you choose to.
To fully understand the concept behind this, i suggest read a java book.. xD But without going into a whole lot of confusing stuff ill give it a go...
The example you gave you are essentially saying SplashActivity is a grandchild of Activity. the Activity is unique to the android platform. here is a basic java example:
Class Car extends Vehicle or Class truck extends Vehicle.. extends does not just give you methods, you inherit methods that override previous ones. if you are looking for a quick way to import packages like "EditText" after typing that use: Cntl + Shift +O.
extends is a java term for inheritance. you can think about it like if you had a Fruit class with certain functionality, then you have an Apple class that extends Fruit. Apple gains all the functionality from Fruit but you can then add new functionality specific to an Apple class.
and if you think this is done for import reasons then you are thinking on a whole different level than the makers of java. try getting an ide that auto imports Classes as you use them in your code, like IntelliJ
Thanks for the information guys.
I knew extends would allow method inheritance, I just though it would also allow package import inheritance.
One of the hurdles I come up against in learning Android development is that even the Google tutorials don't tell you that you need to import different packages for different things - e.g. the Tabs tutorial doesn't explain that you need to import all sorts of stuff and the only way I got it working was that Eclipse is smart and will suggest solutions to your errors.
Thanks again.
Subjective Effect said:
Thanks for the information guys.
I knew extends would allow method inheritance, I just though it would also allow package import inheritance.
One of the hurdles I come up against in learning Android development is that even the Google tutorials don't tell you that you need to import different packages for different things - e.g. the Tabs tutorial doesn't explain that you need to import all sorts of stuff and the only way I got it working was that Eclipse is smart and will suggest solutions to your errors.
Thanks again.
Click to expand...
Click to collapse
The import statement in java is kind of misleading. It's not really importing anything. It just allow you to refer to a class in that java file by using it's short class name (Activity) instead of it's fully qualified name (android.app.Activity). You never really have to use an import statement in your code but if you don't you just wind up having to type the full package name in front every time you use a class name.
So say for instance you didn't have an
import android.app.Activity;
statement in your java file. In order to get the compiler to know what Activity you are talking about you would need to write android.app.Activity everywhere in your code instead of the much simpler way of importing it once and referring to it as Activity.
Hope that made sense.
Also, say for example you had another class in a different package with the same name...
com.example.Activity
If you wanted to use that class in the same java file that you are using android.app.Activity an import is not even going to help you. You would always need to use the fully qualitied name to refer to each Activity class because if you just say "Activity" the compiler don't know if you mean android.app.Activity or com.example.Activity.
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.
Click to expand...
Click to collapse
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 .