Android 从未调用过扩展 SurfaceView 的 onDraw() 方法
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Extended SurfaceView's onDraw() method never called
提问by Gab Royer
I'm trying to modify the SurfaceView I use for doing a camera preview in order to display an overlaying square. However, the onDraw method of the extended SurfaceView is never called.
我正在尝试修改用于进行相机预览的 SurfaceView 以显示重叠的正方形。但是，从未调用扩展 SurfaceView 的 onDraw 方法。
Here is the source :
这是来源：
public 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();
}
}
回答by Gab Royer
Found it on the android-developers Google group. You simply have to add :
在 android-developers Google group 上找到它。您只需添加：
setWillNotDraw(false)
To the constructor. Now if someone could explain me why, that would be greatly appreciated.
给构造函数。现在，如果有人能解释我为什么，那将不胜感激。
回答by dreambig
Minor correction:
小修正：
Adding setWillNotDraw(false) to the constructorwill cause crashes, because the underlying Surface object is not created yet.
将 setWillNotDraw(false) 添加到构造函数会导致崩溃，因为尚未创建底层 Surface 对象。
Instead, put the setWillNotDraw(false) statement into the surfaceCreated() method. This delays the call until there's a real object to work with, and works properly.
相反，将 setWillNotDraw(false) 语句放入 surfaceCreated() 方法中。这会延迟调用，直到有一个真正的对象可以使用，并且可以正常工作。
(and many thanks to the users who posted this solution, it solved a major problem for me)
（非常感谢发布此解决方案的用户，它为我解决了一个主要问题）
回答by HostedMetrics.com
回答by M.Hefny
Based on all above comments I used :
基于我使用的所有上述评论：
Add setWillNotDraw(false) in the onAttachedToWindow() event.
在 onAttachedToWindow() 事件中添加 setWillNotDraw(false)。
@Override
protected void onAttachedToWindow() {
super.onAttachedToWindow();
setWillNotDraw(false);
}
@Override
protected void onAttachedToWindow() {
super.onAttachedToWindow();
setWillNotDraw(false);
}
and it worked.
它奏效了。
