android – 触摸时绘制圆圈

我想画一个用户触摸屏幕的圆圈.

public class MainActivity extends Activity implements OnTouchListener {

LinearLayout layout;
float x=0;
float y=0;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.layout_main);
    layout=(LinearLayout)findViewById(R.id.layout);
    layout.addView(new CustomView(MainActivity.this));
}

public class CustomView extends View {

    Bitmap mBitmap;
    Paint paint;
    public CustomView(Context context) {
        super(context);
        mBitmap = Bitmap.createBitmap(400,800,Bitmap.Config.ARGB_8888);
        paint=new Paint();
        paint.setColor(Color.RED);
        paint.setStyle(Style.FILL);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.setBitmap(mBitmap);
        canvas.drawCircle(x,y,50,paint);
        Toast.makeText(MainActivity.this,"DDD",1).show();
    }
}

@Override
public boolean onTouch(View v,MotionEvent event) {

    if (event.getAction() == MotionEvent.ACTION_DOWN) {
    layout.invalidate();

    }
    return false;
}}

解决方法

我会这样做：

public class TestActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new DrawingView(this));
    }

    class DrawingView extends SurfaceView {

        private final SurfaceHolder surfaceHolder;
        private final Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);

        public DrawingView(Context context) {
            super(context);
            surfaceHolder = getHolder();
            paint.setColor(Color.RED);
            paint.setStyle(Style.FILL);
        }

        @Override
        public boolean onTouchEvent(MotionEvent event) {
            if(event.getAction() == MotionEvent.ACTION_DOWN) {
                if (surfaceHolder.getSurface().isValid()) {
                    Canvas canvas = surfaceHolder.lockCanvas();
                    canvas.drawColor(Color.BLACK);
                    canvas.drawCircle(event.getX(),event.getY(),paint);
                    surfaceHolder.unlockCanvasAndPost(canvas);
                }
            }
            return false;
        }
    }
}