在surfaceview和canvas上绘制Android
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Android drawing on surfaceview and canvas
提问by ChHaupt
I have a "simple" problem. I try to draw on surfaceview. Layout-XML:
我有一个“简单”的问题。我试着在surfaceview上画画。布局-XML：
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:keepScreenOn="true"
android:orientation="vertical" >
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello" />
<SurfaceView
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/imagesurface"
android:layout_height="fill_parent"
android:layout_width="fill_parent"
android:background="#00ff00">
</SurfaceView>
</LinearLayout>
The Activity is a SurfaceHolder.Callback:
Activity 是一个 SurfaceHolder.Callback：
public class OpenCvonAndroidGTDforHOGActivity extends Activity implements SurfaceHolder.Callback{
private SurfaceHolder _surfaceHolder;
private SurfaceView _surfaceView;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
_surfaceView = (SurfaceView)findViewById(R.id.imagesurface);
_surfaceHolder = _surfaceView.getHolder();
_surfaceHolder.addCallback(this);
_surfaceView.setWillNotDraw(false);
}
protected void onDraw(Canvas canvas) {
canvas.drawRGB(255, 0, 255);
}
public void surfaceCreated(SurfaceHolder holder) {
Canvas canvas = null;
try {
canvas = holder.lockCanvas();
synchronized(holder) {
onDraw(canvas);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (canvas != null) {
holder.unlockCanvasAndPost(canvas);
}
}
}
public void showToast(String msg) {
Toast.makeText(getApplicationContext(), msg, Toast.LENGTH_SHORT).show();
}
}
If i call
如果我打电话
_surfaceview.setBackground(Color.RED)in onDraw(...) it works. But
_surfaceview.setBackground(Color.RED)在 onDraw(...) 它工作。但
canvas.drawRGB(255, 0, 255)doesn't work :(
canvas.drawRGB(255, 0, 255)不起作用:(
回答by Vipul Shah
Following Snippet will help you.
遵循 Snippet 将对您有所帮助。
public class SurfaceDemo extends Activity implements SurfaceHolder.Callback {
private static final String TAG = "Svetlin SurfaceView";
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
SurfaceView view = new SurfaceView(this);
setContentView(view);
view.getHolder().addCallback(this);
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
tryDrawing(holder);
}
@Override
public void surfaceChanged(SurfaceHolder holder, int frmt, int w, int h) {
tryDrawing(holder);
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {}
private void tryDrawing(SurfaceHolder holder) {
Log.i(TAG, "Trying to draw...");
Canvas canvas = holder.lockCanvas();
if (canvas == null) {
Log.e(TAG, "Cannot draw onto the canvas as it's null");
} else {
drawMyStuff(canvas);
holder.unlockCanvasAndPost(canvas);
}
}
private void drawMyStuff(final Canvas canvas) {
Random random = new Random();
Log.i(TAG, "Drawing...");
canvas.drawRGB(255, 128, 128);
}
}
回答by cescom
SurfaceViewis composed by a Viewin your current layout and a surface under your layout. If you set a background to the view, you won't see anything of what is happening on the surface.
SurfaceView由View当前布局中的 a 和布局下的表面组成。如果您为视图设置背景，您将看不到表面上发生的任何事情。
回答by Aytunc MATRAC
Did you try
你试过了吗
yourHolder.unlockCanvassAndPost(your_canvas);
