Android Live Wallpaer crashed（NullPointerException, canvas is a null object）but I cannot find where

Question

04-14 12:04:30.971 1639-1938/system_process I/WindowManager: Destroying surface Surface(name=Media:com.android.wallpaper.livepicker/com.android.wallpaper.livepicker.LiveWallpaperChange) called by com.android.server.wm.WindowStateAnimator.destroySurface:2014 com.android.server.wm.WindowStateAnimator.destroySurfaceLocked:881 com.android.server.wm.WindowState.removeLocked:1449 com.android.server.wm.WindowManagerService.removeWindowInnerLocked:2478 com.android.server.wm.WindowManagerService.removeWindowLocked:2436 com.android.server.wm.WindowManagerService.removeWindowLocked:2305 com.android.server.wm.WindowManagerService.removeWindow:2300 com.android.server.wm.Session.remove:193 
04-14 12:04:30.990 3852-3852/tianranwang.livewallpaper D/MainService: dispose
04-14 12:04:31.018 1639-1990/system_process I/WindowManager: Destroying surface Surface(name=tianranwang.livewallpaper.MainService) called by com.android.server.wm.WindowStateAnimator.destroySurface:2014 com.android.server.wm.WindowStateAnimator.destroySurfaceLocked:881 com.android.server.wm.WindowState.removeLocked:1449 com.android.server.wm.WindowManagerService.removeWindowInnerLocked:2478 com.android.server.wm.WindowManagerService.removeWindowLocked:2436 com.android.server.wm.WindowManagerService.removeWindowLocked:2305 com.android.server.wm.WindowManagerService.removeWindow:2300 com.android.server.wm.Session.remove:193 

          --------- beginning of crash
04-14 12:04:31.020 3852-4240/tianranwang.livewallpaper E/AndroidRuntime: FATAL EXCEPTION: Animation Thread
          Process: tianranwang.livewallpaper, PID: 3852
          java.lang.NullPointerException: Attempt to invoke interface method 'void android.view.SurfaceHolder.unlockCanvasAndPost(android.graphics.Canvas)' on a null object reference
              at processing.a2d.PGraphicsAndroid2D.endDraw(Unknown Source)
              at processing.core.PApplet.handleDraw(Unknown Source)
              at processing.core.PSurfaceNone.callDraw(Unknown Source)
              at processing.core.PSurfaceNone$AnimationThread.run(Unknown Source)

On the interface “set wallpaper”, I rotated the screen and the sketch(drawing the live wallpaper) restarted, and the app crashed(not always crashed), and the sketch(live wallpaper) kept running on the background..

Could some one give me a hint? Thanks in advance.

The source code ,that i have found in processing.a2d.PGraphicsAndroid2D.endDraw()

from https://github.com/processing/processing-android/tree/master/core/src/processing

  public void endDraw() {
    if (bitmap == null) return;

    // hm, mark pixels as changed, because this will instantly do a full
    // copy of all the pixels to the surface.. so that's kind of a mess.
    //updatePixels();

//    if (primaryGraphics) {
//      if (canvas != null) {
//        parent.getSurfaceHolder().unlockCanvasAndPost(canvas);
//      }
//    }

    if (primaryGraphics) {
      SurfaceHolder holder = parent.getSurface().getSurfaceHolder();
      if (holder != null) {
        Canvas screen = null;
        try {
          screen = holder.lockCanvas(null);
          if (screen != null) {
            screen.drawBitmap(bitmap, new Matrix(), null);
          }
        } finally {
          if (screen != null) {
            try {
              holder.unlockCanvasAndPost(screen);
            } catch (IllegalStateException ex) {
            }
          }
        }
      } 
    } else {
      // TODO this is probably overkill for most tasks...
      loadPixels();
    }

    // Marking as modified, and then calling updatePixels() in
    // the super class, which just sets the mx1, my1, mx2, my2
    // coordinates of the modified area. This avoids doing the
    // full copy of the pixels to the surface in this.updatePixels().
    setModified();
    super.updatePixels();
  }

The code above may cause this NullPointerException.

I dont have this problem now, because i update the new version of processing library..And the code above is from the new version of the lib. (I cannot see the code from old version)

How can I set breakpoint in android studio, when this NullPointerException in Animation Thread is thrown? — TrW236, Apr 14 '17 at 12:50
I dont have this problem now, because i update the new version of processing library.. — TrW236, Apr 15 '17 at 07:10

Raut Darpan · Answer 1 · 2017-04-15T07:51:16.217

-1

The issue is clear you are pointing a null object reference that is the instance of 'void android.view.SurfaceHolder.unlockCanvasAndPost(android.graphics.Canvas)' is not been created but you are trying to get it so it is throwing error.

 java.lang.NullPointerException: Attempt to invoke interface method 'void android.view.SurfaceHolder.unlockCanvasAndPost(android.graphics.Canvas)' on a null object reference

you can backtrace where the instance of that class is created to get the crash

edited Apr 15 '17 at 07:51

answered Apr 14 '17 at 12:22

Raut Darpan

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I understand this problem. But my Problem is, this exception doesnt say where is the code line(the code that causes the crash) – TrW236 Apr 14 '17 at 12:28
you backtrace it and check where you are using the instance of that clas – Raut Darpan Apr 14 '17 at 12:30
So I cannot debug it.. because I don't know where from my code has problem.. – TrW236 Apr 14 '17 at 12:31
Thats what i am telling backtrace it ... wherever you are using the insatnce – Raut Darpan Apr 14 '17 at 12:32
your trace shows error is in `FATAL EXCEPTION: Animation Thread` – Raut Darpan Apr 14 '17 at 12:35
Do you know How can I set breakpoint in android studio, when this NullPointerException in Animation Thread is thrown? – TrW236 Apr 14 '17 at 12:50
yes, but you'll have to show me the code – Raut Darpan Apr 14 '17 at 12:51
try to find where you are creating the instance of that class – Raut Darpan Apr 14 '17 at 12:52
I didn't create a Canvas(even didn't use a Canvas object). I just used the Processing library. – TrW236 Apr 14 '17 at 12:57
ok so where you are using this lib, put breakpoint there – Raut Darpan Apr 14 '17 at 12:58
I have uploaded the code, that I think is suspect for this NullPointerException – TrW236 Apr 14 '17 at 13:53
Thanks I updated the lib, and the problem is gone – TrW236 Apr 15 '17 at 07:18

Android Live Wallpaer crashed（NullPointerException, canvas is a null object）but I cannot find where

1 Answers1