Question

i wan’t to code a live wallpaper, and i need a list of points that are currently pressed. I store the points in a SpareArray (basically the same than a HashMap, but faster).

Now, when i touch the screen with two fingers (1 and 2) and lift the fingers (first finger 2, than 1), it works. But when i lift finger 1 first, the app crashes. I have to lift my fingers in the reverse order then i pressed them.

@Override
public void onTouchEvent(MotionEvent event) {
    for (int i = 0; i < event.getPointerCount(); i++) {
        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN:
            case MotionEvent.ACTION_POINTER_DOWN:
            case MotionEvent.ACTION_MOVE:
                int pID = event.getPointerId(i);
                Points.put(pID, new Point((int)event.getX(pID), (int)event.getY(pID))); //CRASH HERE
                break;
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_POINTER_UP:
                Points.remove(event.getPointerId(i));
                break;
        }
    }
    super.onTouchEvent(event);
    handler.post(drawRunnable);
}

I always get a “java.lang.IllegalArgumentException: pointerIndex out of range” exception

Thanks, Dominik

EDIT: stack trace

07-16 19:55:58.354: E/AndroidRuntime(4986): FATAL EXCEPTION: main
07-16 19:55:58.354: E/AndroidRuntime(4986): java.lang.IllegalArgumentException: pointerIndex out of range
07-16 19:55:58.354: E/AndroidRuntime(4986):     at android.view.MotionEvent.nativeGetAxisValue(Native Method)
07-16 19:55:58.354: E/AndroidRuntime(4986):     at android.view.MotionEvent.getX(MotionEvent.java:1974)
07-16 19:55:58.354: E/AndroidRuntime(4986):     at net.ta.livewp.LiveWallpaper$xEngine.onTouchEvent(LiveWallpaper.java:103)
07-16 19:55:58.354: E/AndroidRuntime(4986):     at android.service.wallpaper.WallpaperService$IWallpaperEngineWrapper.executeMessage(WallpaperService.java:1047)
07-16 19:55:58.354: E/AndroidRuntime(4986):     at com.android.internal.os.HandlerCaller$MyHandler.handleMessage(HandlerCaller.java:61)
07-16 19:55:58.354: E/AndroidRuntime(4986):     at android.os.Handler.dispatchMessage(Handler.java:99)
07-16 19:55:58.354: E/AndroidRuntime(4986):     at android.os.Looper.loop(Looper.java:137)
07-16 19:55:58.354: E/AndroidRuntime(4986):     at android.app.ActivityThread.main(ActivityThread.java:4575)
07-16 19:55:58.354: E/AndroidRuntime(4986):     at java.lang.reflect.Method.invokeNative(Native Method)
07-16 19:55:58.354: E/AndroidRuntime(4986):     at java.lang.reflect.Method.invoke(Method.java:511)
07-16 19:55:58.354: E/AndroidRuntime(4986):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
07-16 19:55:58.354: E/AndroidRuntime(4986):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:556)
07-16 19:55:58.354: E/AndroidRuntime(4986):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

I believe that you want to be calling event.getX(i) rather than event.getX(pID). getPointerId(i) returns a pointer identifier, rather than an index of a pointer, which is what you want.

More information about this can be found in the MotionEvent docs