空對象引用onReceive BroadcastReceiver

Question

我正在使用兩個活動，主要活動和相機活動。 在mainActivity中，我調用startActivity（new Intent（this，CameraActivity））;

現在，當攝像機活動開始時， onCreate（）為：

@Override
public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.camera_preview);
    View myView= (View) findViewById(R.id.camera_previeww);
    myView.setSystemUiVisibility(View.SYSTEM_UI_FLAG_HIDE_NAVIGATION);

    cameraID= Camera.CameraInfo.CAMERA_FACING_FRONT;
    mCamera=openCamera(cameraID);
    mCamera.startPreview();

    IntentFilter filter = new IntentFilter();
    filter.addAction(Tabbed.BROADCAST_ACTION_TABBED);
    LocalBroadcastManager bm = LocalBroadcastManager.getInstance(this);
    bm.registerReceiver(mBroadcastReceiver, filter);


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

openCamera（int cameraID）方法是：

    public  Camera openCamera(int cameraIDD){
         Camera c=null;
         try{
             c=Camera.open(cameraIDD);
         }catch (Exception e){
             Log.d("Camera Activity", e.getMessage());
         }
          return c;

     }

我也使用的是BroadcastReceiver：

        private BroadcastReceiver mBroadcastReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {

        byte [] data=new byte[3];
        if (intent.getAction().equals(Tabbed.BROADCAST_ACTION_TABBED)) {
            data = intent.getByteArrayExtra(Tabbed.EXTRA_PARAM_BYTE);
        }
        if (data[FINGER]==MIDDLE_FINGER && data[TYPE]==SINGLE_TAP){
            //switchCamera();
            //releaseCamera();
            //mCamera=Camera.open();
        }
        else if (data[FINGER]==MIDDLE_FINGER && data[TYPE]==DOUBLE_TAP){
            // HAVE TO GO BACK
            kill_activity();
        }
        else if (data[FINGER]==INDEX_FINGER && data[TYPE]==SINGLE_TAP){
            mCamera.takePicture(null, null, mPicture);
        }

    // kill activity

    }
};

和其他一些方法：

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

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

這是崩潰：

    FATAL EXCEPTION: main
                                                           Process: com.etu.goglove, PID: 6008
                                                           java.lang.NullPointerException: Attempt to invoke virtual method 'void android.hardware.Camera.takePicture(android.hardware.Camera$ShutterCallback, android.hardware.Camera$PictureCallback, android.hardware.Camera$PictureCallback)' on a null object reference
                                                               at com.etu.goglove.CameraActivity$2.onReceive(CameraActivity.java:155)
                                                               at android.support.v4.content.LocalBroadcastManager.executePendingBroadcasts(LocalBroadcastManager.java:297)
                                                               at android.support.v4.content.LocalBroadcastManager.access$000(LocalBroadcastManager.java:46)
                                                               at android.support.v4.content.LocalBroadcastManager$1.handleMessage(LocalBroadcastManager.java:116)
                                                               at android.os.Handler.dispatchMessage(Handler.java:102)
                                                               at android.os.Looper.loop(Looper.java:154)
                                                               at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                               at java.lang.reflect.Method.invoke(Native Method)
                                                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

有了這些，我想在收到廣播意向時拍照。 因此，在我的活動開始之后，我打開mCamera，當我收到意向書時，我進行了拍照或返回。 第一次，我可以拍照，然后完成活動。 如果我嘗試從mainActivity重新啟動cameraActivity，調用onActiv （）相機中的startActivity（intent）處於打開狀態，並且它不為null（已通過調試器檢查），但是這一次，當我進入onReceive（）方法時， mCamera始終為null，因此我在mCamera上獲得了一個空對象引用！（當我嘗試執行mCamera.takePicture（）時 ）不知道如何...

謝謝！

Answer 1

    private BroadcastReceiver mBroadcastReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {

        byte [] data=new byte[3];
        if (intent!=null && intent.getAction().equals(Tabbed.BROADCAST_ACTION_TABBED)) {
            data = intent.getByteArrayExtra(Tabbed.EXTRA_PARAM_BYTE);

        if (data[FINGER]==MIDDLE_FINGER && data[TYPE]==SINGLE_TAP){
            //switchCamera();
            //releaseCamera();
            //mCamera=Camera.open();
        }
        else if (data[FINGER]==MIDDLE_FINGER && data[TYPE]==DOUBLE_TAP){
            // HAVE TO GO BACK
            kill_activity();
        }
        else if (data[FINGER]==INDEX_FINGER && data[TYPE]==SINGLE_TAP){
            mCamera.takePicture(null, null, mPicture);
        }
}
    // kill activity

    }
};