单点触控

package com.example.crazy;

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 NewView extends View{
//定义圆的出事位置
public float currentX=40;
public float currentY=50;
//定义画笔
Paint p=new Paint();
    public NewView(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
    }    
    public NewView(Context context, AttributeSet attrs) {
        super(context, attrs);
        // TODO Auto-generated constructor stub
    }    
    public NewView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        // TODO Auto-generated constructor stub
    }
    @Override
        protected void onDraw(Canvas canvas) {
            // TODO Auto-generated method stub
            super.onDraw(canvas);
            //设置画笔的颜色
            p.setColor(Color.RED);
                       //绘制一个小圆
            canvas.drawCircle(currentX, currentY, 15, p);
            
        }
    @Override
        public boolean onTouchEvent(MotionEvent event) {
            // TODO Auto-generated method stub
              //设置当前组件的两个属性
        this.currentX=event.getX();
        this.currentY=event.getY();
               //通知组件重置
        this.invalidate();
                //返回true代表时间已经处理
            return true;
        }

}
    

<LinearLayout 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" 
    android:orientation="vertical"
    >

   
<com.example.crazy.NewView
    
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    />
</LinearLayout>

主页面MainActivity

package com.example.day1_two;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

  
    
}

效果图如下：圆随着鼠标二移动