Android相机解锁媒体记录器

Question

我想编写一个通过智能手机摄像头录制视频的应用程序。我找到这个网站寻求帮助：http://developer.android.com/guide/topics/media/camera.html#custom-camera

我正在使用该源代码开始。

我的主要活动：

 public class MainActivity extends Activity {

        protected static final String TAG = null;
        private Camera mCamera;
        private CameraPreview mPreview;
        private MediaRecorder mMediaRecorder=null;
        public static final int MEDIA_TYPE_IMAGE = 1;
        public static final int MEDIA_TYPE_VIDEO = 2;
        private boolean isRecording = 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 onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);

            // 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);


         // Add a listener to the Capture button
         final Button captureButton = (Button) findViewById(R.id.button_capture);
         captureButton.setOnClickListener(
             new View.OnClickListener() {
                 @Override
                 public void onClick(View v) {
                     if (isRecording) {
                         // stop recording and release camera
                         mMediaRecorder.stop();  // stop the recording
                         releaseMediaRecorder(); // release the MediaRecorder object
                         mCamera.lock();         // take camera access back from MediaRecorder

                         // inform the user that recording has stopped
                         captureButton.setText("Capture");
                         //setCaptureButtonText("Capture");
                         isRecording = false;
                     } else {
                         // initialize video camera
                         if (prepareVideoRecorder()) {
                             // Camera is available and unlocked, MediaRecorder is prepared,
                             // now you can start recording
                             mMediaRecorder.start();

                             // inform the user that recording has started
                             captureButton.setText("Stop");
                             //setCaptureButtonText("Stop");
                             isRecording = true;
                         } else {
                             // prepare didn't work, release the camera
                             releaseMediaRecorder();
                             // inform user
                         }
                     }
                 }
             }
         );
        }

        @SuppressLint("NewApi") private boolean prepareVideoRecorder(){

            mCamera = getCameraInstance();
            Log.d(TAG, "mcamera object: " + mCamera.getNumberOfCameras());
            mMediaRecorder = new MediaRecorder();

            // Step 1: Unlock and set camera to MediaRecorder
            try{
            mCamera.unlock();
            }catch (RuntimeException r){
        Log.d(TAG, "mcamera unlock: " + r.getMessage());
            }
            mMediaRecorder.setCamera(mCamera);

            // Step 2: Set sources
            mMediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
            mMediaRecorder.setVideoSource(MediaRecorder.VideoSource.CAMERA);

            // Step 3: Set a CamcorderProfile (requires API Level 8 or higher)
            mMediaRecorder.setProfile(CamcorderProfile.get(CamcorderProfile.QUALITY_HIGH));

            // Step 4: Set output file
            mMediaRecorder.setOutputFile(getOutputMediaFile(MEDIA_TYPE_VIDEO).toString());

            // Step 5: Set the preview output
            mMediaRecorder.setPreviewDisplay(mPreview.getHolder().getSurface());

            // Step 6: Prepare configured MediaRecorder
            try {
                mMediaRecorder.prepare();
            } catch (IllegalStateException e) {
                Log.d(TAG, "IllegalStateException preparing MediaRecorder: " + e.getMessage());
                releaseMediaRecorder();
                return false;
            } catch (IOException e) {
                Log.d(TAG, "IOException preparing MediaRecorder: " + e.getMessage());
                releaseMediaRecorder();
                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 (mMediaRecorder != null) {
                mMediaRecorder.reset();   // clear recorder configuration
                mMediaRecorder.release(); // release the recorder object
                mMediaRecorder = null;
                mCamera.lock();           // lock camera for later use
            }
        }

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

        /** Create a File for saving an image or video */
        private static File getOutputMediaFile(int type){
            // To be safe, you should check that the SDCard is mounted
            // using Environment.getExternalStorageState() before doing this.

            File mediaStorageDir = new File(Environment.getExternalStoragePublicDirectory(
                      Environment.DIRECTORY_PICTURES), "MyCameraApp");
            // This location works best if you want the created images to be shared
            // between applications and persist after your app has been uninstalled.

            // Create the storage directory if it does not exist
            if (! mediaStorageDir.exists()){
                if (! mediaStorageDir.mkdirs()){
                    Log.d("MyCameraApp", "failed to create directory");
                    return null;
                }
            }

            // Create a media file name
            String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
            File mediaFile;
            if (type == MEDIA_TYPE_IMAGE){
                mediaFile = new File(mediaStorageDir.getPath() + File.separator +
                "IMG_"+ timeStamp + ".jpg");
            } else if(type == MEDIA_TYPE_VIDEO) {
                mediaFile = new File(mediaStorageDir.getPath() + File.separator +
                "VID_"+ timeStamp + ".mp4");
            } else {
                return null;
            }

            return mediaFile;
        }

    }

我的相机预览课：

/** A basic Camera preview class */
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
    private SurfaceHolder mHolder;
    private Camera mCamera;
    private static final String TAG = "Preview";

    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(TAG, "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) {
        // 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){
          // ignore: tried to stop a non-existent preview
        }

        // set preview size and 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 starting camera preview: " + e.getMessage());
        }
    }
}

但是当我在我的 samsung s5660 API 2.3.3 上运行该应用程序时，我收到此错误：

06-07 19:55:48.859: D/(20274): mcamera object: 1
06-07 21:10:19.159: D/(20465): mcamera unlock: null
06-07 19:55:48.859: W/dalvikvm(20274): threadid=1: thread exiting with uncaught exception (group=0x40018578)
06-07 19:55:48.859: E/AndroidRuntime(20274): FATAL EXCEPTION: main
06-07 19:55:48.859: E/AndroidRuntime(20274): java.lang.NullPointerException
06-07 19:55:48.859: E/AndroidRuntime(20274):    at com.example.videocapture.MainActivity.prepareVideoRecorder(MainActivity.java:118)
06-07 19:55:48.859: E/AndroidRuntime(20274):    at com.example.videocapture.MainActivity.access$5(MainActivity.java:111)
06-07 19:55:48.859: E/AndroidRuntime(20274):    at com.example.videocapture.MainActivity$1.onClick(MainActivity.java:91)
06-07 19:55:48.859: E/AndroidRuntime(20274):    at android.view.View.performClick(View.java:2485)
06-07 19:55:48.859: E/AndroidRuntime(20274):    at android.view.View$PerformClick.run(View.java:9080)
06-07 19:55:48.859: E/AndroidRuntime(20274):    at android.os.Handler.handleCallback(Handler.java:587)
06-07 19:55:48.859: E/AndroidRuntime(20274):    at android.os.Handler.dispatchMessage(Handler.java:92)
06-07 19:55:48.859: E/AndroidRuntime(20274):    at android.os.Looper.loop(Looper.java:130)
06-07 19:55:48.859: E/AndroidRuntime(20274):    at android.app.ActivityThread.main(ActivityThread.java:3687)
06-07 19:55:48.859: E/AndroidRuntime(20274):    at java.lang.reflect.Method.invokeNative(Native Method)
06-07 19:55:48.859: E/AndroidRuntime(20274):    at java.lang.reflect.Method.invoke(Method.java:507)
06-07 19:55:48.859: E/AndroidRuntime(20274):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
06-07 19:55:48.859: E/AndroidRuntime(20274):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
06-07 19:55:48.859: E/AndroidRuntime(20274):    at dalvik.system.NativeStart.main(Native Method)

空指针异常在 lin 118 prepareVideoRecorder():

// Step 1: Unlock and set camera to MediaRecorder
        mCamera.unlock();

当应用程序启动时，会显示相机，当我点击“捕获”按钮时会引发此错误。现在我认为问题“mCamera = getCameraInstance();”在此函数中再次调用，第一个是在相机预览类的主 Activity 中创建的。

我在“mCamera = getCameraInstance();”之后添加了一个日志标签在 prepareVideoRecorder() 中查看它是否真的为空，但您看不到报告说“06-07 19:55:48.859: D/(20274): mcamera object: 1”

Answer 1

解决方案是删除行 mCamera = getCameraInstance();在 prepareVideoRecorder() 函数中。

Answer 2

mMediaRecorder is null，你应该正确初始化它。
请看here。