跟随手指的小球

package com.example.shangqiuju.myapplication;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.view.View;

/**
 * 自定义组件
 * Created by shangqiuju on 2021/7/30.
 */

public class DrawView extends View{
    public float currentX = 40;
    public float currentY = 50;

    /**
     *
     * @param context
     */
    public DrawView(Context context){
        super(context);
        //TODO Auto-generated constructor stub
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //创建画笔
        Paint p = new Paint();
        //设置画笔的颜色
        p.setColor(7777777);
        //绘制一个画图（作为小球）
        canvas.drawCircle(currentX,currentY,15,p);
    }
}

首先自定义控件DrawView

然后为程序绑定一个OnTouchListener的监听，手指在触摸屏上移动，将不断触发摸屏事件

事件监听中负责的坐标将被传入DrawView组件，并通知该组件重绘

package com.example.shangqiuju.myapplication;

import android.app.Application;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.view.MotionEvent;
import android.view.View;
import android.widget.LinearLayout;

/**
 * Created by shangqiuju on 2021/7/30.
 */

public class SecondActivity extends AppCompatActivity {

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.second_activity);
        //获取局部文件中的LinearLayout容器
        LinearLayout root = (LinearLayout) findViewById(R.id.rot);
        //创建DrawView组件
        final DrawView draw = new DrawView(this);
        //设置自定义组件的最大宽度、高度
        draw.setMinimumWidth(300);
        draw.setMinimumHeight(500);
        //为draw组件绑定Touch事件
        draw.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View view, MotionEvent motionEvent) {
                //修改draw组件的currentX，currentY两个属性
                draw.currentX = motionEvent.getX();
                draw.currentY = motionEvent.getY();
                //通知draw组织重绘
                draw.invalidate();
                //返回true表明处理方法已经处理该事件
                return false;
            }
        });
        root.addView(draw);
    }
}