使用GestureDetector在自定义绘制上绘制小部件

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.View;

public class CustomView extends View {
    private Paint paint;
    private float x, y;
    private GestureDetector gestureDetector;

    public CustomView(Context context) {
        super(context);
        paint = new Paint();
        paint.setColor(Color.RED);
        paint.setStyle(Paint.Style.FILL);

        gestureDetector = new GestureDetector(context, new GestureDetector.SimpleOnGestureListener() {
            @Override
            public boolean onTouchEvent(MotionEvent event) {
                switch (event.getAction()) {
                    case MotionEvent.ACTION_DOWN:
                        x = event.getX();
                        y = event.getY();
                        break;
                    case MotionEvent.ACTION_MOVE:
                        float newX = event.getX();
                        float newY = event.getY();
                        float dx = newX - x;
                        float dy = newY - y;
                        x = newX;
                        y = newY;
                        invalidate(); // 重绘视图
                        break;
                }
                return true;
            }
        });
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawCircle(x, y, 50, paint);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        return gestureDetector.onTouchEvent(event);
    }
}