1 package cn.coreqi.view;
 2
 3 import android.content.Context;
 4 import android.graphics.Canvas;
 5 import android.graphics.Color;
 6 import android.graphics.Paint;
 7 import android.util.AttributeSet;
 8 import android.view.MotionEvent;
 9 import android.view.View;
10
11 public class DrawView extends View {
12     private float currentX = 40f;
13     private float currentY = 50f;
14
15     //定义并创建画笔
16     private Paint p = new Paint();
17
18     public DrawView(Context context) {
19         super(context);
20     }
21
22     public DrawView(Context context, AttributeSet attrs) {
23         super(context, attrs);
24     }
25
26     //当该组件将要绘制它的内容时触发该方法
27     @Override
28     protected void onDraw(Canvas canvas) {
29         super.onDraw(canvas);
30         //设置画笔的颜色
31         p.setColor(Color.RED);
32         //绘制一个小圆(作为小球)
33         canvas.drawCircle(currentX,currentY,15F,p);
34     }
35
36     //为该组件的触碰事件重写事件处理方法
37     @Override
38     public boolean onTouchEvent(MotionEvent event) {
39         //修改currentX，currentY两个成员变量
40         currentX = event.getX();
41         currentY = event.getY();
42         //通知当前组件重新绘制自己
43         invalidate();
44         //返回true表明该处理方法已经处理该事件
45         return true;
46     }
47 }

 1 package cn.coreqi;
 2
 3 import androidx.appcompat.app.AppCompatActivity;
 4
 5 import android.os.Bundle;
 6 import android.widget.LinearLayout;
 7 import cn.coreqi.view.DrawView;
 8
 9
10 public class MainActivity extends AppCompatActivity {
11
12     @Override
13     protected void onCreate(Bundle savedInstanceState) {
14         super.onCreate(savedInstanceState);
15         //新建LinearLayout布局容器
16         LinearLayout layout = new LinearLayout(this);
17         //设置该Activity显示layout
18         setContentView(layout);
19         //创建我们自定义的View组件
20         DrawView draw = new DrawView(this);
21         //设置自定义组件的最小宽度、高度
22         draw.setMinimumWidth(300);
23         draw.setMinimumHeight(500);
24         layout.addView(draw);
25     }
26 }

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
 3     xmlns:app="http://schemas.android.com/apk/res-auto"
 4     xmlns:tools="http://schemas.android.com/tools"
 5     android:layout_width="match_parent"
 6     android:layout_height="match_parent"
 7     tools:context=".MainActivity">
 8
 9     <cn.coreqi.view.DrawView
10         android:id="@+id/drawView"
11         android:layout_width="match_parent"
12         android:layout_height="match_parent" />
13
14 </androidx.constraintlayout.widget.ConstraintLayout>