Android入门之onTouchEvent触碰事件的示例详解

package org.mk.Android.demo;
 
import android.content.Context;
import android.graphics.canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
 
public class CircleView extends View {
    public float X = 50;
    public float Y = 50;
    //创建画笔
    Paint paint = new Paint();
 
    public CircleView(Context context, AttributeSet set)
    {
        super(context,set);
    }
 
    @Override
    public void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        paint.setColor(Color.RED);
        canvas.drawCircle(X,Y,50,paint);
    }
 
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        this.X = event.getX();
        this.Y = event.getY();
        //通知组件进行重绘
        this.invalidate();
        return true;
    }
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="Http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
    <org.mk.android.demo.CircleView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
</RelativeLayout>

package org.mk.android.demo;
 
import androidx.appcompat.app.AppCompatActivity;
 
import android.os.Bundle;
 
public class MainActivity extends AppCompatActivity {
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
}

 switch (event.getAction() & MotionEvent.ACTION_MASK) {
        // 单指
        case MotionEvent.ACTION_DOWN:
            
            break;
        // 双指
        case MotionEvent.ACTION_POINTER_DOWN: