Develop Reference

My device will flash back to the background after the multilingual handover jump

BaseActivity.java
Language switching
Intent
OnClickListener
Error demo
No error message was prompted.

You are using old style of language switching which were deprecated and removed after releasing android 8, It completely get removed. However, if you want to use your application for android prior to 26, you have to change your code on language switching Image as follow:
Configuration config = new Configuration(resources.getConfiguration());
New instance of Configuration have to be passed to resources.updateConfiguration();. above line will solve your problem.
On the other hand if you want to publish your application for higher api level, follow link below:
#Override
protected void attachBaseContext(Context newBase){
Configuration configuration = new Configuration(newBase.getResoureces().getConfiguration());
configuration.setLocale(/* selected locale which you have to get from user or your app configuration*/);
super.attachBaseContext(newBase.createConfigurationContext(configuration));
}
Override above method for each activity which you have declared;

java.lang.Exception when implementing method in android activity

This might be a very naive question but I can't get this java.lang.Exception error to go away. I also just started learning java and android so... this might be an easy problem to solve.
So I have a main activity in android and I want to implement a weka ml classifier within the app. Right now I'm just trying to load some data.
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ml_classifiers ml_object = new ml_classifiers();
int number = ml_object.loadData();
Trying to load data...
public class ml_classifiers {
public int loadData() {
ConverterUtils.DataSource source = new ConverterUtils.DataSource("C:/Users/Seth/Desktop/iris.arff");
Instances data = source.getDataSet();
int num = data.numInstances();
return num;
}
}
Why does java.lang.exception occur?

Why does java.lang.exception occur?
In the future, when you encounter crashes, use LogCat to examine the Java stack trace associated with the crash. If you do not understand the stack trace or otherwise cannot identify the problem, and you want help here, post the stack trace along with the code. As it stands, we have to guess exactly what is going wrong in your app.
In this case, while you may be crashing elsewhere, you will definitely crash with:
ConverterUtils.DataSource source = new ConverterUtils.DataSource("C:/Users/Seth/Desktop/iris.arff");
assuming that this is code in your Android app.
You are attempting to read data from C:/Users/Seth/Desktop/iris.arff. That is a path to a file on a Windows machine. Android is not Windows. There are ~2 billion Android devices in use, and none of them have access to files on your Windows' machine's desktop.
You need to get this data onto the Android device, such as:
by putting it in the assets/ directory in your module (to package it with your app), then using AssetManager to get an InputStream on that asset, hopefully passing that directly to ConverterUtils.DataSource
downloading the file from the Internet, perhaps into internal storage (e.g., getCacheDir())
expecting the user to copy the file onto their device by hand, such as via external storage

LibVLC fails to show subtitles for streamed video

I tried to create a video player on android device, which could stream videos from local server. I found an this example. I followed to the guideline and at the end I was able to play local video on my device. Then I started to modify this project. I set VideoActivity as launcher activity and commented out all data received from previous activity. I modified initialization of media from
Media m = new Media(libvlc, media);
mMediaPlayer.setMedia(m);
to
Uri uri = Uri.parse("http://samples.mplayerhq.hu/MPEG-4/embedded_subs/1Video_2Audio_2SUBs_timed_text_streams_.mp4");
Media m = new Media(libvlc, uri);
mMediaPlayer.setMedia(m);
Added 2 new methods (as you see, those methods are dummy methods simply to see the result)
private void setSubtitles(){
MediaPlayer.TrackDescription[] tds = mMediaPlayer.getSpuTracks();
mMediaPlayer.setSpuTrack(tds[tds.length - 1].id);
}
private void seekTo(long time) {
mMediaPlayer.setTime(time);
}
And called them on play event
#Override
public void onEvent(MediaPlayer.Event event) {
VideoActivity player = mOwner.get();
switch(event.type) {
case MediaPlayer.Event.EndReached:
Log.d(TAG, "MediaPlayerEndReached");
player.releasePlayer();
break;
case MediaPlayer.Event.Playing:
---> player.seekTo(1000);
---> player.setSubtitles();
case MediaPlayer.Event.Paused:
case MediaPlayer.Event.Stopped:
default:
break;
}
}
But when ever I tried to play the video, I got 12401-12591/? A/libc﹕ ### ABORTING: INVALID HEAP ADDRESS IN dlfree. I get this error some seconds after subtitles ar shown (Also subtitles are too small). This error is shown only when I try to show subtitles. Without subtitles video is playing without any error.
I tried to play this video on VLC application and it was able to show subtitles. I tried to create new project - got the same error. I analysed VLC android source code and it looks that they are using almost the same logic for loading subtitles (Only setting different surfaceViews for video and subtitles, but it gave me the same error). So what am I missing? What does cause player to brake and how to fix it? Maybe there is already working example of code for showing subtitles.

Problems about ProGuard when build up APK

When I build up the APK, I find out the KEYs of JSON changed when I use the Network. I just fund out that it is a problem about ProGuard.
I have added "#SerializedName" to every variables in Request/Response Folder. And added
-keepclassmembernames class com.mygroup.myapp.protocol.response.Responsexx {
public *;}
for every Resquest/Response JAVA program, which took me much time but doesn't work.
My app crashed after I get the response, the logcat says com.b.a.b.w cannot be cast to com.mygroup.myapp.b.g , and I have located the error:
private List<UserInfoModel> mUserList = new ArrayList<>();
private UserInfoModel UserInfo = new UserInfoModel();
if (mUserList.size()>0)
UserInfo = mUserList.get(0); //CRASHED HERE
I am sure that the size of mUserList is 1, I made a toast and saw it.
Please Help Me. Much Thanks.
Moreover, the IDE I am using is Android Studio.

Android Libgdx Fatal signal 11(SIGSEGV) ,code 1, fault addr 0x0

I know this is an error with accessing memory outside the readspace but i have absolutely no idea how to fix this. I'm new to android, so i don't exactly know how to print out a more detailed error list from logcat in eclipse. I've tried everything from disposing literally everything, to calling System.gc to setting all my variables to null. However, whenever i switch screens the fatal signal occurs. I just need someone to tell me what exactly is going on or how i could get more details about the error.

I had the same error, what solved it was to make sure i'm on the UI thread, like this:
Gdx.app.postRunnable(new Runnable() {
#Override
public void run() {
// Your crashing code here
}
});

In my case i received same error when i try to create a new body and attach it's fixture, from beginContact (inside Contact Listener). After i moved outside Contact Listener my body creation everything was ok. Probably some conflict appears in Fixture createFixture (FixtureDef def) because according to manual: Contacts are not created until the next time step.