android - 试图将相机切换回前面但出现异常

Question

尝试将相机切换回前面但出现异常。找不到 问题请检查并帮助..

error:- 01-27 11:49:00.376: E/AndroidRuntime(30767):
java.lang.RuntimeException: Unable to start activity
ComponentInfo{com.vdrecord/com.vdrecord.AndroidVideoCapture}:
java.lang.NullPointerException

我的代码:-

 public class AndroidVideoCapture extends Activity{
    private static final String TAG = "CameraRecorderActivity";
  private Camera myCamera;
    private MyCameraSurfaceView myCameraSurfaceView;
    private MediaRecorder mediaRecorder;
    private static String val="yes";
    private Button useOtherCamera;
  Button myButton;
  SurfaceHolder surfaceHolder;
  boolean recording;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        recording = false;
        setContentView(R.layout.activity_android_video_capture);
        useOtherCamera = (Button) findViewById(R.id.useOtherCamera);
        useOtherCamera.setOnClickListener(
                new View.OnClickListener() {
                    @Override
                     public void onClick(View v) {
            //Get Camera for preview
            myCamera = getCameraInstance();
        }
        });
        FrameLayout myCameraPreview = (FrameLayout)findViewById(R.id.videoview);
        myCameraPreview.addView(myCameraSurfaceView);
        myButton = (Button)findViewById(R.id.mybutton);
        myButton.setOnClickListener(myButtonOnClickListener);
        myButton.setOnClickListener(myButtonOnClickListener);

        if(myCamera == null){
            System.out.println("PRINT TRACK--7 ");
         Toast.makeText(AndroidVideoCapture.this,
           "Fail to get Camera",
           Toast.LENGTH_LONG).show();
        }

        myCameraSurfaceView = new MyCameraSurfaceView(this, myCamera);
        }

    Button.OnClickListener myButtonOnClickListener
    = new Button.OnClickListener(){

  @Override
  public void onClick(View v) {
   // TODO Auto-generated method stub
   if(recording){
                // stop recording and release camera
                mediaRecorder.stop();  // stop the recording
                releaseMediaRecorder(); // release the MediaRecorder object

                //Exit after saved
                finish();
   }else{

    //Release Camera before MediaRecorder start
    releaseCamera();

          if(!prepareMediaRecorder()){
           Toast.makeText(AndroidVideoCapture.this,
             "Fail in prepareMediaRecorder()!\n - Ended -",
             Toast.LENGTH_LONG).show();
           finish();
          }

    mediaRecorder.start();
    recording = true;
    myButton.setText("STOP");
   }
  }};

  public int getFrontCameraId() {
      CameraInfo ci = new CameraInfo();
      for (int i = 0 ; i < Camera.getNumberOfCameras(); i++) {
          Camera.getCameraInfo(i, ci);
          if ((val=="yes") && (ci.facing == CameraInfo.CAMERA_FACING_FRONT))
          {
              val="no";
              return i;
          }

      }

      return CameraInfo.CAMERA_FACING_BACK; // No front-facing camera found
  }
    public Camera getCameraInstance(){
  // TODO Auto-generated method stub
        Camera c = null;
        try {
          int index = getFrontCameraId();
          if (index != -1)
          {
           c = Camera.open(index);
         //   c = Camera.open(); // attempt to get a Camera instance
        }else{
             c = Camera.open(index);
        }
        }
        catch (Exception e){
          Log.d(TAG, "Error setting camera preview: " + e.getMessage());
            // Camera is not available (in use or does not exist)
        }
        return c; // returns null if camera is unavailable
  }

  private boolean prepareMediaRecorder(){
     myCamera = getCameraInstance();
     mediaRecorder = new MediaRecorder();

     myCamera.unlock();
     mediaRecorder.setCamera(myCamera);

     mediaRecorder.setAudioSource(MediaRecorder.AudioSource.CAMCORDER);
     mediaRecorder.setVideoSource(MediaRecorder.VideoSource.CAMERA);

     mediaRecorder.setProfile(CamcorderProfile.get(CamcorderProfile.QUALITY_LOW));

     mediaRecorder.setOutputFile("/sdcard/myvideo.mp4");
        mediaRecorder.setMaxDuration(60000); // Set max duration 60 sec.
        mediaRecorder.setMaxFileSize(5000000); // Set max file size 5M

     mediaRecorder.setPreviewDisplay(myCameraSurfaceView.getHolder().getSurface());

     try {
         mediaRecorder.prepare();
     } catch (IllegalStateException e) {
         releaseMediaRecorder();
         Log.d(TAG, "Error setting camera preview: " + e.getMessage());
         return false;
     } catch (IOException e) {
         releaseMediaRecorder();
         Log.d(TAG, "Error setting camera preview: " + e.getMessage());
         return false;
     }
     return true;

  }

    @Override
    protected void onPause() {
        super.onPause();
        releaseMediaRecorder();       // if you are using MediaRecorder, release it first
        releaseCamera();              // release the camera immediately on pause event
    }

    private void releaseMediaRecorder(){
        if (mediaRecorder != null) {
            mediaRecorder.reset();   // clear recorder configuration
            mediaRecorder.release(); // release the recorder object
            mediaRecorder = null;
            myCamera.lock();           // lock camera for later use
        }
    }

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

  public class MyCameraSurfaceView extends SurfaceView implements SurfaceHolder.Callback{

  private SurfaceHolder mHolder;
     private Camera mCamera;

  public MyCameraSurfaceView(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);
     }

  @Override
  public void surfaceChanged(SurfaceHolder holder, int format, int weight,
    int height) {
         // If your preview can change or rotate, take care of those events here.
         // Make sure to stop the preview before resizing or reformatting it.

         if (mHolder.getSurface() == null){
           // preview surface does not exist
           return;
         }

         // stop preview before making changes
         try {
             mCamera.stopPreview();

         } catch (Exception e){
           Log.d(TAG, "Error setting camera preview: " + e.getMessage());
           // ignore: tried to stop a non-existent preview
         }

         // make any resize, rotate or reformatting changes here

         // start preview with new settings
         try {
             mCamera.setPreviewDisplay(mHolder);
             mCamera.startPreview();

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

  @Override
  public void surfaceCreated(SurfaceHolder holder) {
   // TODO Auto-generated method stub
   // 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(TAG, "Error setting camera preview: " + e.getMessage());
         }
  }

  @Override
  public void surfaceDestroyed(SurfaceHolder holder) {
   // TODO Auto-generated method stub

  }
  }
  }

  Error Log:- 01-27 11:49:00.376: E/AndroidRuntime(30767): FATAL
    EXCEPTION: main 01-27 11:49:00.376: E/AndroidRuntime(30767):
    java.lang.RuntimeException: Unable to start activity
    ComponentInfo{com.vdrecord/com.vdrecord.AndroidVideoCapture}:
    java.lang.NullPointerException 01-27 11:49:00.376:
     E/AndroidRuntime(30767):   at
    android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1968)
    01-27 11:49:00.376: E/AndroidRuntime(30767):    at
    android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1993)
    01-27 11:49:00.376: E/AndroidRuntime(30767):    at
    android.app.ActivityThread.access$600(ActivityThread.java:127) 01-27
    11:49:00.376: E/AndroidRuntime(30767):  at
    android.app.ActivityThread$H.handleMessage(ActivityThread.java:1159)
    01-27 11:49:00.376: E/AndroidRuntime(30767):    at
    android.os.Handler.dispatchMessage(Handler.java:99) 01-27
    11:49:00.376: E/AndroidRuntime(30767):  at
    android.os.Looper.loop(Looper.java:137) 01-27 11:49:00.376:
    E/AndroidRuntime(30767):    at
    android.app.ActivityThread.main(ActivityThread.java:4507) 01-27
    11:49:00.376: E/AndroidRuntime(30767):  at
    java.lang.reflect.Method.invokeNative(Native Method) 01-27
    11:49:00.376: E/AndroidRuntime(30767):  at
    java.lang.reflect.Method.invoke(Method.java:511) 01-27 11:49:00.376:
    E/AndroidRuntime(30767):    at
    com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:980)
    01-27 11:49:00.376: E/AndroidRuntime(30767):    at
    com.android.internal.os.ZygoteInit.main(ZygoteInit.java:747) 01-27
    11:49:00.376: E/AndroidRuntime(30767):  at
    dalvik.system.NativeStart.main(Native Method) 01-27 11:49:00.376:
    E/AndroidRuntime(30767): Caused by: java.lang.NullPointerException
    01-27 11:49:00.376: E/AndroidRuntime(30767):    at
    android.view.ViewGroup.addView(ViewGroup.java:3158) 01-27
    11:49:00.376: E/AndroidRuntime(30767):  at
    android.view.ViewGroup.addView(ViewGroup.java:3145) 01-27
    11:49:00.376: E/AndroidRuntime(30767):  at
    com.vdrecord.AndroidVideoCapture.onCreate(AndroidVideoCapture.java:51)
    01-27 11:49:00.376: E/AndroidRuntime(30767):    at
    android.app.Activity.performCreate(Activity.java:4465) 01-27
    11:49:00.376: E/AndroidRuntime(30767):  at
    android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1052)
    01-27 11:49:00.376: E/AndroidRuntime(30767):    at
    android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1932)

Answer 1

在切换到其他实例之前停止相机上一个实例:

if (camera != null) {
        camera.stopPreview();
        camera.setPreviewCallback(null);
        camera.release();
        camera = null;
        surfaceholder.removeCallback(CameraActivity.this);
        surfaceholder = null;
}

并完成当前相机 Activity ，调用相同相机 Activity 的开始 Intent 。