package org.crazyit.ui;


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;

/**
 * Description:<br>
 * 网站: <a href="http://www.crazyit.org">疯狂Java联盟</a><br>
 * Copyright (C), 2001-2020, Yeeku.H.Lee<br>
 * This program is protected by copyright laws.<br>
 * Program Name:<br>
 * Date:<br>
 * @author Yeeku.H.Lee kongyeeku@163.com<br>
 * @version 1.0
 */
public class DrawView extends View
{
	private float currentX = 40f;
	private float currentY = 50f;
	// 定义并创建画笔
	private Paint p = new Paint();

	public DrawView(Context context)
	{
		super(context);
	}

	public DrawView(Context context, AttributeSet set)
	{
		super(context, set);
	}

	@Override
	public void onDraw(Canvas canvas)
	{
		super.onDraw(canvas);
		// 设置画笔的颜色
		p.setColor(Color.RED);
		// 绘制一个小圆（作为小球）
		canvas.drawCircle(currentX, currentY, 15F, p);
	}

	// 为该组件的触碰事件重写事件处理方法
	@Override
	public boolean onTouchEvent(MotionEvent event)
	{
		// 修改currentX、currentY两个属性
		currentX = event.getX();
		currentY = event.getY();
		// 通知当前组件重绘自己
		invalidate();
		// 返回true表明该处理方法已经处理该事件
		return true;
	}
}

package org.crazyit.ui;

import android.app.Activity;
import android.os.Bundle;
import android.widget.LinearLayout;

/**
 * Description:<br>
 * 网站: <a href="http://www.crazyit.org">疯狂Java联盟</a><br>
 * Copyright (C), 2001-2020, Yeeku.H.Lee<br>
 * This program is protected by copyright laws.<br>
 * Program Name:<br>
 * Date:<br>
 * @author Yeeku.H.Lee kongyeeku@163.com<br>
 * @version 1.0
 */
public class MainActivity extends Activity
{
	@Override
	public void onCreate(Bundle savedInstanceState)
	{
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		// 获取布局文件中的LinearLayout容器
		LinearLayout root = findViewById(R.id.root);
		// 创建DrawView组件
		DrawView draw = new DrawView(this);
		// 设置自定义组件的最小宽度、高度
		draw.setMinimumWidth(300);
		draw.setMinimumHeight(500);
		root.addView(draw);
	}
}

<?xml version="1.0" encoding="utf-8"?>
<!-- 定义一个线性布局容器 -->
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
	xmlns:tools="http://schemas.android.com/tools"
	tools:context=".MainActivity"
	android:id="@+id/root"
	android:orientation="vertical"
	android:layout_width="match_parent"
	android:layout_height="match_parent">
</LinearLayout>