返回活动后 CameraSource 触发空异常

Question

我有一个初始化条形码检测的活动。然后我去另一个活动，当我按下后退按钮时，它会触发这个异常的循环：

com.example.myapp E/CameraSource: Exception thrown from receiver.
                                  java.lang.NullPointerException
                      at com.google.android.gms.vision.CameraSource$zzb.run(Unknown Source)
                      at java.lang.Thread.run(Thread.java:841)

如果我坚持并再次进入另一个活动，它会引发另一个异常：

com.example.myapp E/AndroidRuntime: FATAL EXCEPTION: main
                                                                      Process: com.example.myapp, PID: 22942
                                                                      java.lang.NullPointerException
                                                                          at com.google.android.gms.vision.CameraSource$zzb.release(Unknown Source)
                                                                          at com.google.android.gms.vision.CameraSource.release(Unknown Source)
                                                                          at com.example.myapp.CameraActivity$3.surfaceDestroyed(CameraActivity.java:184)
                                                                          at android.view.SurfaceView.updateWindow(SurfaceView.java:586)
                                                                          at android.view.SurfaceView.onWindowVisibilityChanged(SurfaceView.java:240)
                                                                          at android.view.View.dispatchWindowVisibilityChanged(View.java:8495)
                                                                          at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1087)
                                                                          at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1087)
                                                                          at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1087)
                                                                          at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1087)
                                                                          at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1087)
                                                                          at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1087)
                                                                          at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1537)
                                                                          at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1254)
                                                                          at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6602)
                                                                          at android.view.Choreographer$CallbackRecord.run(Choreographer.java:805)
                                                                          at android.view.Choreographer.doCallbacks(Choreographer.java:605)
                                                                          at android.view.Choreographer.doFrame(Choreographer.java:575)
                                                                          at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:791)
                                                                          at android.os.Handler.handleCallback(Handler.java:733)
                                                                          at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                          at android.os.Looper.loop(Looper.java:136)
                                                                          at android.app.ActivityThread.main(ActivityThread.java:5476)
                                                                          at java.lang.reflect.Method.invokeNative(Native Method)
                                                                          at java.lang.reflect.Method.invoke(Method.java:515)
                                                                          at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1268)
                                                                          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1084)
                                                                          at dalvik.system.NativeStart.main(Native Method)

CameraSource 在 onCreate 中是这样初始化的：

    final CameraSource cameraSource = new CameraSource.Builder(this, barcodeDetector)
            .setRequestedFps(15f)
            .setAutoFocusEnabled(true)
            .build();
    mCameraView.getHolder().addCallback(new SurfaceHolder.Callback() {
        @Override
        public void surfaceCreated(SurfaceHolder holder) {
            try {
                if (ActivityCompat.checkSelfPermission(getApplicationContext(), Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED)
                    return;
                cameraSource.start(holder);
            } catch (IOException e) {
                Log.e(getClass().getName(), e.getMessage());
            }
        }

        @Override
        public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        }

        @Override
        public void surfaceDestroyed(SurfaceHolder holder) {
            cameraSource.release();
        }
    });

Answer 1

我将相机初始化代码从 onCreate 移动到 onResume 并像这样保护相机释放：

mCameraView.getHolder().addCallback(new SurfaceHolder.Callback() {
        ...
        @Override
        public void surfaceDestroyed(SurfaceHolder holder) {
            if (mCameraSource != null) {
                mCameraSource.release();
                mCameraSource = null;
            }
        }
    });

现在可以了。