我开发一个应用程序，它需要打开我的Galaxy Nexus的设备的手电筒。我刚才提到了这里的帖子

I am developing an app which needs to open the flashlight of my Galaxy Nexus device. I have referred to the post here

LED手电筒Galaxy Nexus的控制由什么API？

public class TestCamera extends Activity implements SurfaceHolder.Callback{
Camera mCamera;
public static SurfaceView preview;
public static SurfaceHolder mHolder;
public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    preview = (SurfaceView) findViewById(R.id.camSurface);
    mHolder = preview.getHolder();
    mCamera = Camera.open();
    try {
        mCamera.setPreviewDisplay(mHolder);
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    Button onLEDbtn = (Button) findViewById(R.id.onLED_btn);
    onLEDbtn.setOnClickListener(new OnClickListener(){

        public void onClick(View v) {
            // TODO Auto-generated method stub
            Toast.makeText(getApplicationContext(), "test", Toast.LENGTH_SHORT).show();
            Parameters params = mCamera.getParameters();
            params.setFlashMode(Parameters.FLASH_MODE_TORCH);
            mCamera.setParameters(params);      
            mCamera.startPreview();
        }

    });
}



}


    public void surfaceChanged(SurfaceHolder holder, int format, int width,
            int height) {
        // TODO Auto-generated method stub

    }


    public void surfaceCreated(SurfaceHolder holder) {
        // TODO Auto-generated method stub
        mHolder = holder;
        try {
            mCamera.setPreviewDisplay(mHolder);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }


    public void surfaceDestroyed(SurfaceHolder holder) {
        // TODO Auto-generated method stub
         mCamera.stopPreview();
            mHolder = null;
    }




}

清单：

<uses-permission android:name="android.permission.CAMERA" />
<uses-feature android:name="android.hardware.camera" />

不过，我的手电筒仍然无法开关。任何人都可以指出我的错误？谢谢

However, I still cant switch on the flashlight. Could anyone point out my errors? Thanks

推荐答案

您必须设置回调 mHolder.addCallback（本）;

you must to set call back mHolder.addCallback(this);