Android Simple Camera Control App crashes when returning from Stopped

Issue

I was working through the developer.Android Tutorials on building a Camera App but I always encounter the following problem: When my app is put into the background, i.e. Stopped according to the activity lifecycle, and I try to return to it it crashes, telling me the App has stopped working.

I searched other questions, but none of them seemed to have this same problem or I wasn't able to recognise it.

I tried to figure out the minimum amount of code for this error to occur. The (only) Activity:

public class CameraActivity extends ActionBarActivity {

private Camera mCamera;
private CameraPreview mPreview;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_camera_layout);

    // if device hardware has a camera
    if (checkCameraHardware(this))
        // Create an instance of Camera
        mCamera = getCameraInstance();

    // Create our Preview view and set it as the content of our activity.
    mPreview = new CameraPreview(this, mCamera);
    FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
    preview.addView(mPreview);


}

/** Check if this device has a camera */
private boolean checkCameraHardware(Context context) {
    if (context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA)){
        // this device has a camera
        return true;
    } else {
        // no camera on this device
        return false;
    }
}

/** A safe way to get an instance of the Camera object. */
public static Camera getCameraInstance(){
    Camera c = null;
    try {
        c = Camera.open(); // attempt to get a Camera instance
    }
    catch (Exception e){
        // Camera is not available (in use or does not exist)
    }
    return c; // returns null if camera is unavailable
}

@Override
public void onPause() {
    super.onPause();
    releaseCamera();              // release the camera immediately on pause event
}

private void releaseCamera(){
    if (mCamera != null){
        mCamera.stopPreview();      // stop the preview
        mCamera.release();        // release the camera for other applications
        mCamera = null;
    }
}

@Override
public void onResume() {
    super.onResume();

    if (mCamera == null)
        mCamera = getCameraInstance();
}


}

The CameraPreview is instantiated using this class:

public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
    private SurfaceHolder mHolder;
    private Camera mCamera;

public CameraPreview(Context context, Camera camera) {
    super(context);
    mCamera = camera;

    // Install a SurfaceHolder.Callback so we get notified when the
    // underlying surface is created and destroyed.
    mHolder = getHolder();
    mHolder.addCallback(this);
    // deprecated setting, but required on Android versions prior to 3.0
    mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
}

public void surfaceCreated(SurfaceHolder holder) {
    // The Surface has been created, now tell the camera where to draw the preview.
    try {

         mCamera.setPreviewDisplay(holder);
         mCamera.startPreview();

    } catch (IOException e) {
        Log.d("PandaHero", "Error setting camera preview: " + e.getMessage());
    }
}

public void surfaceDestroyed(SurfaceHolder holder) {
    // empty. Take care of releasing the Camera preview in your activity.
}

public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
    // .. same as in the example of the link
}
}

As for error messages, it always shows me that surfaceCreated() is called after release(). This made me think that I have to be missing some important reinstantiation of the camera or preview somewhere. I tried to stop the preview and release the camera within surfaceDestroyed(), onStop() and also to reopen the preview inside onStart() but the error persisted. Also, no crashes occur if I do not include the Preview in the first place (but then my users wouldn't be able to see it either, so that's no option).

So yeah, I think there is something vital I am missing here in terms of making use of the life cycle.

Edit: The Error message I mentioned.

03-02 14:33:45.553  15462-15462/com.example.vrevru.viewlate_camerasetupsimple E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Method called after release()
        at android.hardware.Camera.setPreviewDisplay(Native Method)
        at android.hardware.Camera.setPreviewDisplay(Camera.java:428)
        at com.example.thorsten.viewlate_camerasetupsimple.CameraPreview.surfaceCreated(CameraPreview.java:32)
        at android.view.SurfaceView.updateWindow(SurfaceView.java:639)
        at android.view.SurfaceView.onWindowVisibilityChanged(SurfaceView.java:262)
        at android.view.View.dispatchWindowVisibilityChanged(View.java:7440)
        at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042)
        at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042)
        at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042)
        at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042)
        at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042)
        at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042)
        at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1237)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1009)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4236)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)
        at android.view.Choreographer.doCallbacks(Choreographer.java:555)
        at android.view.Choreographer.doFrame(Choreographer.java:525)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711)
        at android.os.Handler.handleCallback(Handler.java:615)
        at android.os.Handler.dispatchMessage(Handler.java:92)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:4872)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
        at dalvik.system.NativeStart.main(Native Method)

Solution

Alright,

I think I got a solution, though I am not sure it's the nicest one.

I noticed that I never told my app create a new preview after releasing the old one in onPause(). I thought Android would handle that because the documentation always stated that no setup leading up to the first creation of the app needed to be redone. Apparently, I misunderstood them (though what do they mean with that?).

So I added a manual removal of the old CameraPreview object from my Framelayout in onPause(), then created a new one and added it to the Framelayout in onResume().

@Override
public void onPause() {
    super.onPause();
    releaseCamera();              // release the camera immediately on pause event
    // two new lines for removing the old CameraPreview
    FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
    preview.removeView(mPreview);
}
@Override
public void onResume() {
    super.onResume();

    if (mCamera == null)
    {
        mCamera = getCameraInstance();
        // three new lines, creating a new CameraPreview, then adding it to the FrameLayout
        mPreview = new CameraPreview(this, mCamera);
        FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
        preview.addView(mPreview);
    }
}

However, while now the error has disappeared and my problem is solved (the app doesn't crash anymore), I have just put some seemingly pretty costly lines of code into my Pause and Resume functions. The transition to other apps and back has slowed down noticable. Is there a more intelligent way to do this?

Answered By - user4623666