Question

我无法让相机工作（我的意思是，它确实有效，但与此同时我得到一个NullPointerException）。它被抛出onSurfaceCreated方法：

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

public CameraView(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);
    Log.i("xcamerx", String.valueOf(mCamera));
}

@Override
public void surfaceCreated(SurfaceHolder holder) {
    // The Surface has been created, now tell the camera where to draw the preview.
    try {
        Log.i("xcamera", String.valueOf(mCamera));
        Log.i("xcamera", String.valueOf(holder));

        mCamera.setPreviewDisplay(holder);
        mCamera.startPreview();
    } catch (IOException e) {
        Log.d("CameraError", "Error starting 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("CameraError", "Error starting camera preview: " + e.getMessage());
    }
}

public void pause()
{    
    mHolder.removeCallback(this);       
}

public void resume()
{    
    mHolder.addCallback(this);      
}

}

在我的SurfaceView中实现。在这个视图的活动中，我得到一个Camera实例：

公共类CameraActivity扩展了Activity {

private Camera mCamera;
private CameraView mPreview;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_camera);

    // Create an instance of Camera
    mCamera = getCameraInstance();      
    // Create our Preview view and set it as the content of our activity.
    mPreview = new CameraView(this, mCamera);
    FrameLayout preview = (FrameLayout) findViewById(R.id.camera_view);
    preview.addView(mPreview);
}





@Override
protected void onPause() {
    // TODO Auto-generated method stub
    super.onPause();
    mPreview.pause();

}



@Override
protected void onResume() {
    // TODO Auto-generated method stub
    super.onResume();
    mPreview.resume();
}



/** 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
}

}

然后作为参数传递给SurfaceView构造函数。在LogCat中，当我打印Camera对象时（就像我发布的第一个代码块一样），我得到了几次有效的Camera对象，但是现在有一些空值出现的原因超出了我的理解范围。有什么想法吗？

onSurfaceCreared方法中相机对象的空指针

0 个答案: