Android: NoClassDefFoundError

My Android Eclipse project uses two external jars: Flurry and Admob. They work fine until I upgraded Android SDK to 4.0.3. Then there is forced close due to java.lang.NoClassDefFoundError: com.flurry.android.FlurryAgent.


The fix is to check these two jars in the "Order and Export" tab.

Android: proguard cannot find symbols in Flurry

When exporting signed signed application package in Eclipse, proguard emits warnings about not being able to find Flurry symbols, then aborts.

The fix is to add

-libraryjars /path/to/FlurryAgent.jar

to proguard.cfg

Unity: How to test iOS Unity Apps without using Xcode

Xcode is slow when building Unity iOS apps. It is not a good option for testing Unity iOS apps since it could take several minutes to build the app.

You cannot use the Game panel in Unity to test iOS apps which handles touch events because the Game panel does not emulate touch event with mouse. If you use the Game panel, Input.TouchCount is always zero since there is no touch events.

You need to use Unity Remote to test Unity iOS apps. It is a iOS app which can be downloaded from Apple App Store freely and installed on your iOS devices. Before testing your app, connect your iOS device to your Mac, then run Unity Remote on your iOS device and select your Mac machine. In Unity, run your app, the Game panel will stream video display to Unity Remote and Unity Remote will pass touch events from your iOS device to the Game panel. This way you can test your Unity iOS app with all the iOS events.

Unity: Problem with invalid signature on iOS

If you build Unity project for iOS and see this error when running the app:

The application does not have a valid signature


And your development provisional profile are OK. It can be caused by having more than one development provisional profiles. You can use organizer to remove extra development provisional profiles and only keep the generic one. This should fix the problem.

Unity: problem with Xcode 4.3.2

Currently Unity basic edition does not work with Xcode 4.3.1 and 4.3.2. The error is:

You are using Unity iPhone Basic. You are not allowed to remove the Unity splash screen from your game


The workaround is generate your Xcode project and build it with Xcode 4.3 or older version.


Until now there is no fix yet. Unity is aware of this issue and promised a fix in the next release.


http://forum.unity3d.com/threads/126820-Unity-3.5-and-iOS-5.1

Android: cannot use Admob due to String types not allowed at 'configChanges'

I was trying to use Admob in my app and added this to my AndroidManifest.xml:


<activity

android:name="com.google.ads.AdActivity"    android:configChanges="keyboard|keyboardHidden|orientation|screenLayout|uiMode|screenSize|smallestScreenSize" >

</activity>

then there is a build error:

Sting types not allowed at 'configChanges' with value 'keyboard|keyboardHidden|orientation|screenLayout|uiMode|screenSize|smallestScreenSize'.

Turns out to use Admob you need to change build target to be at least 13. You can still let your app run on lower Android versions even your build target is 13. build target is only for build. Your minimum required OS version is specified by uses-sdk minSdkVersion.

http://stackoverflow.com/questions/7902121/admob-cant-display-ads-because-of-configchanges

Android: Project build target vs minSdkVersion

Project build target is the SDK version you build your app with. minSdkVersion is the minimum SDK version you want your app to run on.

You want to build your app with latest SDK since it may contain bug fixes not available in older SDK, but you can still run your app on an older SDK. For example, you can set project build target to be 15 (Android 4.0) but set minSdkVersion to be 8 (Android 2.2).

You set project build target by right click your project and choose "properties", then go to "Android" and select "Project build target".

You set minSdkVersion by setting  <uses-sdk android:minSdkVersion="x" />  in AndroidManifest.xml, before application node.

Android: Eclipse no output in LogCat

For unknown reason my eclipse has no output in LogCat. This is very bad since the output at exception goes to LogCat, without which it is impossible to know what is wrong when app is forced to close.

Luckily found a solution on Stackoverflow: switch to DDMS perspective and click the device running the app, then switch back to Java perspective.

http://stackoverflow.com/questions/2250112/why-doesnt-logcat-show-anything-in-my-android

Alternative to iOS UDID

Apple has started to reject apps using UDID

Things to do:
1. update Flurry
2. update Admob
https://groups.google.com/forum/?fromgroups#!topic/google-admob-ads-sdk/dz7cep43THA
3. update AdWhirl

Replace UDID with CFUUIDCreate 
http://stackoverflow.com/questions/9858850/an-alternative-to-the-device-udid-preparing-ourselves 

Error: iPhone Distribution: No profiles currently match

Saw this error when building for distribution.

solution at stackoverflow:

http://stackoverflow.com/questions/3608851/iphone-distribution-no-profiles-currently-match

Basically
1. in organizer under library/certificates refresh to get new developer and distribution certificates
2. go to provisioning portal, under provisioning/distribution, create a new provisioning profile, download and double click.

Error: application executable is missing a required architecture armv6

Saw this error when submitting iOS app to itunes connect.

solution from stackoverflow:

http://stackoverflow.com/questions/7053466/application-executable-is-missing-a-required-architecture-armv6

Basically change architecture from "armv7" to "armv6 armv7".

Give your function a bad name and ruins it all

I do not know about other compilers, but I happen to use a compiler which does not protect system function names, that is, if you define a function read(), it overrides some system function read() and messed up all kinds of stuff. If you rename it as readxxx(), then everything works.

This sounds really stupid, but be careful when you name your functions. Adding a prefix maybe a good idea.

Android: things to do before publishing your app

Assuming Eclipse is used to develop Android app. After the development work is done, before publishing your app in Google Play or Amazon Android Store, there are still several things need to be done:

Add proguard.config=proguard.cfg to project.properties. Although proguard.config is automatically generated, it is not turned on by default. You need to manually add it to project.properties to enable it in your building process, otherwise your apk file contains symbols which are easier to be reverse engineered.


Disable debug in AndroidManifest.xml, then export the app. Check proguard directory is created under your project directory. mapping.txt contains mapped symbols whereas seeds.txt contains unmapped symbols. Send the apk file to your email and open it on your Android device, then you can install it on your Android device and test it. You can also put it on a private web server and download it on your Android device to install it.

Create an EULA and a dialog to show EULA to the user the first time the app is run. Unlike iPhone App Store, Google Play does not have a general EULA for Android apps, so you had better to have one by yourself to provide at least some shelter.

Android: write string to a file

FileOutputStream os = new FileOutputStream(fileName);

OutputStreamWriter osw = new OutputStreamWriter(os); 

osw.write(str);

osw.flush();

osw.close();

Do not use

DataOutputStream os = new DataOutputStream(new FileOutputStream(file));

os.writeUTF(str); // this will write a weird char at the beginning of the file

os.writeUTF writes the string with a modified UTF-8 encoding. If the file is opened by WebView as HTML, a weird char shows up at the beginning of the file. 

Android: ProgressDialog does not show up

Android ProgressDialog can be used like iOS ActivityIndicator to show the app is blocked on some time-consuming work.

You cannot just show a ProgressDialog and then busy waiting a flag. If so the dialog will not show up. You need to busy wait in another thread.

Example:

final ProgressDialog dialog = ProgressDialog.show(

          MyActivity.this, "",

          "Loading. Please wait...", true);

new Thread(new Runnable() {

  public void run() {

    while (!isWorkDone)

      Thread.yield();

    dialog.dismiss();

  }

}).start();

Android: optimize app loading time

No one likes to wait for an app to launch for more than several seconds. It is critical to optimize the app loading time.

My app loads a large 3D model at launching. It is a custom binary format consisting of vertex array and index array. The vertex format is interleaved since it is from an iOS app. Each vertex is 8 floats: 3 for position, 3 for normal, and 2 for texture coordinates.

It is not suitable for Android if you use Java instead of NDK. So I write a small Java program to convert the binary file so that there is a position array, a normal array and a texture coordinates array. When I load the mesh, I can read all positions to a byte array, wrap it as a byte buffer, use it as a float buffer, then copy it to a direct float buffer, which could be used by OpenGL ES. Same for normals and tex coords. This optimization speeds up the file I/O by 50%. Although it is still kind of slow (4 secs). Most of time is spent copying from the byte array wrapped as float buffer to the direct float buffer.

Since 4 seconds is still slow for launching an app, I ran the mesh loading code in another thread, and add a flag for mesh ready. If mesh is not ready, the render code will skip rendering the mesh. With this change, the app is very fast to load.

Android: run time-consuming work in another thread

Many times you want to run time-consuming work in another thread instead of main thread because UI will stop response if you run it in main thread, and the user will frustrate.

It is easy to implement:

Just wrap up the time-consuming code with

new Thread(new Runnable() {

  public void run() {

  //... time-consuming work

  }

}).start();

Android: Using Flurry to gather information

Flurry is a mobile app analytics service for many platforms including iOS and Android.

It is very easy to use. Just register an account, then create a new app. It will generate an app id for your new app, then you can download its SDK.

For Android, you just need to add an external Jar to your Eclipse project, then add severa lines of code to init and end Flurry sessions.  You can then log events in your app.

Some usages:

1. log screen size and dpi, so that you will know distribution of screen sizes, and prioritize your layout effort
2. log time spent in time-consuming procedures, to prioritize optimization effort
3. log frame rate for OpenGL ES, so that you may exclude some slow device from your app
4. log supported OpenGL ES version. If OpenGL ES 2.0 is supported by 90% devices, you may start working on it
5. log pages viewed, to rank the pages

Java: inline initializer for Map

Flurry has a function

FlurryAgent.logEvent(String event, Map<String,String> parameters)

It can be called with an inline initializer like this

FlurryAgent.logEvent("event", new HashMap<String,String>() {{
  put("key1","val1");
  put("key2","val2");
}});

Timing in Java

Timing in Java is easy.

long start = System.nanoTime();

long time = System.nanoTime()-start;

The unit is nanosecond. The long type is enough for 300 years.

Eclipse CDT: index not working

Eclipse CDT indexing of source codes is very important for large projects. Without it you cannot highlight a class or function and right click "open declaration". Manually go through the source tree to find a file is a nightmare.

The index of my C++ project was suddenly broken. I cannot highlight a class member and right click "open declaration". Also when I edit a header file, the outline panel does not show the class members.

I find this link
http://wiki.eclipse.org/CDT/User/FAQ#Why_does_Open_Declaration_.28F3.29_not_work.3F_.28also_applies_to_other_functions_using_the_indexer.29
but it does not work for me.

Then it occurs to me Eclipse no longer treated my project as a C++ project. Finally I got a solution:

Choose menu File/New/Convert to a C/C++ project. It took a while to index the source code. After that, everything works like a charm.

Android: taking screenshots

In eclipse, choose DDMS perspective, then click the button for screenshot.

Android: null pointer exception after changing view id in xml

Sometimes after you modify view id in layout xml files, you get null pointer exception in seemingly irrelevant code due to findViewById returns null when finding irrelevant views.

This is due to modifying view id messed up the view id definitions of all views. A simple solution is to clean up your project and rebuild it (usually it should be auto rebuilt after cleaning up).

OpenGL: objects with color are displayed as black or white

When displaying with OpenGL, if the normals are not normalized, the objects may become black if the normals are too small and white if the normals are too big.

two constants affects normalization

GL_NORMALIZE: normalize normals. it is slower

GL_RESCALE_NORMAL: only scale normals based on scaling factor in modelview matrix. faster than GL_NORMALIZE. If the normals are not normalized from beginning, this won't fix them.

Android: artifacts in OpenGL ES display when dithering disabled

Android shows artifacts in OpenGL ES display when dithering is disabled. This is because by default the OpenGL view uses 16 bit color for performance reasons. Not all Android device supports 32 bit color. For better display dithering should not be disabled.

Android: exception when downloading web page without network connection

URL url = new URL("http://blah");

InputStream is = null;

is = url.openStream();

When there is no network connection, is is null. Using it will cause null pointer exception.

Check to make sure is is not null before using it.

Android: App name and icon not updated

Sometimes after you modify app name and icon through AndroidManifest.xml and rebuild it and install it, but the app name and icon on your device do not change. You may need to uninstall it and install again to see the change.

Android: How to delete development apps

Development apps installed through eclipse cannot be deleted by Android Market.

At home screen, press menu button, select Uninstall, then click the apps you want to install. Press back button once it is done.

Android: OpenGL ES: segfault displaying modified vertex array

I fixed a bug causing segfault when displaying a modified vertex array with OpenGL ES in Android.

Problem: I have an activity which contains an OpenGL view and a list view on top of it. The OpenGL view displays a vertex array by glDrawElements. Each time the user tap a list item in the list view, the onClick event handler will update the vertex array used by the OpenGL view. Segmentation fault will happen if I click the list items enough number of times (usually 4-10 times).

The vertex array is a FloatBuffer. When I modify it I call position() to move the position to the end of the buffer, then call put(value) in a loop to add new vertices. After that, I call position(0) to move the position to the beginning of the buffer.

I found that instead of using put(value), if I use put(position, value) to add new vertices, I won't get segfault. Then I noticed some weird triangles were displayed shortly when I click the list view.

Then I realized the event handler of the list view uses different threads than the thread displaying the vertex array in the OpenGL view. Therefore if I change the position attribute of the FloatBuffer, it could be used by the drawing thread and cause segfault.

Lessons learned:
1. make sure vertex array is not modified by other threads when displaying it
2. when debugging this kind of problem, try to removing problematic codes part by part until narrow down to one line of code

Endianness issues in Java

Java is big endian. C endianness depends on CPU. In iphone simulator on x86 based Mac, C is little endian. Jave has problem loading a binary file saved by an iphone app run in iphone simulator. When saving the binary file to be opened by a Java program, each variable needs to reverse the byte order.

Android: cannot load files larger than 1MB

Android cannot load files larger than 1MB under assets or res/raw.

This is a known issue:
http://stackoverflow.com/questions/2860157/load-files-bigger-than-1m-from-assets-folder

The workaround is to rename the file as .png so that android won't zip it.

Android problem with ArrayList of String

I was trying to read a text file to an ArrayList of String. The code is like this:

public class SymptomCategory {

 private ArrayList<String> mCategory;

 public SymptomCategory (InputStream is) {

 

  String str="";

  StringBuffer buf = new StringBuffer();   

  BufferedReader reader = new BufferedReader(new InputStreamReader(is));

  if (is!=null) {       

   try {

    while ((str = reader.readLine()) != null) { 

     System.out.println(str);

     mCategory.add(new String(str));

     buf.append(str + "\n" );

    }

   } catch (IOException e) {

    // TODO Auto-generated catch block

    e.printStackTrace();

   }    

  }  

 }

 public ArrayList<String> getCategory() {

  return mCategory;

 }




}

The problem was that I can only read the first line of the file.

I fixed the problem by adding the following at the beginning of the constructor:

  mCategory = new ArrayList<String>();

Android problem: cannot find text file under assets

I put symp.txt under assets and use the following code to load it:

    AssetManager am = context.getAssets();

    InputStream is;

try {

    is = am.open("symp.txt");

    mCategory = new SymptomCategory(is);

} catch (IOException e) {

    e.printStackTrace();

}

However I got exception when opening the file.

The problem was fixed by cleaning up the project and let it auto recompile.