Question

所以，问题很简单，之前问了很多次。但是如何使这个代码工作？这个例子发布在这里Extended SurfaceView's onDraw() method never called，答案是：Gab Royer给出了 setWillNotDraw（false）。

提前致谢。

class CameraPreviewView extends SurfaceView {

protected final Paint rectanglePaint = new Paint();

public CameraPreviewView(Context context, AttributeSet attrs) {
    super(context, attrs);
    rectanglePaint.setARGB(255, 200, 0, 0);
    rectanglePaint.setStyle(Paint.Style.FILL);
    rectanglePaint.setStrokeWidth(2);
}

@Override
protected void onDraw(Canvas canvas){
    canvas.drawRect(new Rect(10,10,200,200), rectanglePaint);
    Log.w(this.getClass().getName(), "On Draw Called");
 }
}

public class CameraPreview extends Activity implements SurfaceHolder.Callback{

private SurfaceHolder holder;
private Camera camera;

@Override
protected void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);

    // We remove the status bar, title bar and make the application fullscreen
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
            WindowManager.LayoutParams.FLAG_FULLSCREEN);

    // We set the content view to be the layout we made
    setContentView(R.layout.camera_preview);

    // We register the activity to handle the callbacks of the SurfaceView
    CameraPreviewView surfaceView = (CameraPreviewView) findViewById(R.id.camera_surface);
    holder = surfaceView.getHolder();

    holder.addCallback(this);
    holder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
}

public void surfaceChanged(SurfaceHolder holder, int format, int width,
        int height) {

    Camera.Parameters params = camera.getParameters();

    params.setPreviewSize(width, height);
    camera.setParameters(params);

    try {
        camera.setPreviewDisplay(holder);
    } catch (IOException e) {
        e.printStackTrace();
    }
    camera.startPreview();
}

public void surfaceCreated(SurfaceHolder holder) {
    camera = Camera.open();
}

public void surfaceDestroyed(SurfaceHolder holder) {
    camera.stopPreview();
    camera.release();   
  }
}

日志：

04-03 17:55:17.119: E/AndroidRuntime(951): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
        04-03 17:55:17.119: E/AndroidRuntime(951):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
        04-03 17:55:17.119: E/AndroidRuntime(951):  at android.app.ActivityThread.access$1500(ActivityThread.java:117)
        04-03 17:55:17.119: E/AndroidRuntime(951):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
        04-03 17:55:17.119: E/AndroidRuntime(951):  at android.os.Handler.dispatchMessage(Handler.java:99)
        04-03 17:55:17.119: E/AndroidRuntime(951):  at android.os.Looper.loop(Looper.java:123)
        04-03 17:55:17.119: E/AndroidRuntime(951):  at android.app.ActivityThread.main(ActivityThread.java:3683)
        04-03 17:55:17.119: E/AndroidRuntime(951):  at java.lang.reflect.Method.invokeNative(Native Method)
        04-03 17:55:17.119: E/AndroidRuntime(951):  at java.lang.reflect.Method.invoke(Method.java:507)
        04-03 17:55:17.119: E/AndroidRuntime(951):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
        04-03 17:55:17.119: E/AndroidRuntime(951):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
        04-03 17:55:17.119: E/AndroidRuntime(951):  at dalvik.system.NativeStart.main(Native Method)
        04-03 17:55:17.119: E/AndroidRuntime(951): Caused by: java.lang.ClassCastException: android.view.SurfaceView
        04-03 17:55:17.119: E/AndroidRuntime(951):  at com.example.CameraPreview.onCreate(CameraPreview.java:32)
        04-03 17:55:17.119: E/AndroidRuntime(951):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
        04-03 17:55:17.119: E/AndroidRuntime(951):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)

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