通过继承View类，我们可以自定义自己需求的复杂控件。本例实现了一个自定义的时钟。

效果如下：

代码如下：

package com.example.test;

import java.util.Calendar;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.os.Handler;
import android.util.AttributeSet;
import android.view.View;

public class Clock extends View implements Runnable {
	//表盘图像资源ID
	private int clockImageResourceID;
	//表盘图像缩放比例
	private float scale;
	private Bitmap bitmap;
	//原始图像中表盘中心点横坐标相当于图像宽度的比例
	private float centerWidthScale;
	//原始图像中表盘中心点纵坐标相当于图像高度的比例
	private float centerHeightScale;
	//在原始表盘中分针的长度
	private int minuteSize;
	//在原始表盘中时针的长度
	private int hourSize;
	
	private Handler handler=new Handler();
	
	public Clock(Context context, AttributeSet attrs) {
		super(context, attrs);
		// TODO Auto-generated constructor stub
		//本例未使用命名空间 null
		clockImageResourceID=attrs.getAttributeResourceValue(null,"clockImageSrc",0);
		if(clockImageResourceID>0){
			bitmap=BitmapFactory.decodeResource(getResources(), clockImageResourceID);
		}
		scale=attrs.getAttributeFloatValue(null, "scale", 1);
		centerWidthScale=attrs.getAttributeFloatValue(null, "centerWidthScale" ,bitmap.getHeight()/2);
		centerHeightScale=attrs.getAttributeFloatValue(null, "centerHeightScale" ,bitmap.getWidth()/2);
		//将时针分针的长度缩放
		minuteSize=(int)(attrs.getAttributeIntValue(null, "minuteSize", 0)*scale);
		hourSize=(int)(attrs.getAttributeIntValue(null, "hourSize", 0)*scale);
		int currentSecond=Calendar.getInstance().get(Calendar.SECOND);
		//当秒钟在12点方向时 执行run方法
		handler.postDelayed(this, (60-currentSecond)*1000);
	}

	//view分离时调用
	@Override
	protected void onDetachedFromWindow() {
		// TODO Auto-generated method stub
		super.onDetachedFromWindow();
		handler.removeCallbacks(this);
	}

	public void run() {
		// TODO Auto-generated method stub
		//重绘
		invalidate();
		//重新设定定时器60s后启用
		handler.postDelayed(this, 60*1000);
	}

	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		// TODO Auto-generated method stub
		super.onMeasure(widthMeasureSpec, heightMeasureSpec);
		//根据图像的实际大小等比例设置view的大小
		setMeasuredDimension((int)(bitmap.getWidth()*scale), (int)(bitmap.getHeight()*scale));
	}

	@Override
	protected void onDraw(Canvas canvas) {
		// TODO Auto-generated method stub
		super.onDraw(canvas);
		Paint paint=new Paint();
		Rect src=new Rect();
		Rect target=new Rect();
		src.left=0;
		src.top=0;
		src.right=bitmap.getWidth();
		src.bottom=bitmap.getHeight();
		
		target.left=0;
		target.top=0;
		target.bottom=(int)(src.bottom*scale);
		target.right=(int)(src.right*scale);
		//画表盘
		canvas.drawBitmap(bitmap, src, target,paint);
		//计算表盘中心点的横坐标
		float centerX=bitmap.getWidth()*scale*centerWidthScale;
		//计算表盘中心点的纵坐标
		float centerY=bitmap.getHeight()*scale*centerHeightScale;
		canvas.drawCircle(centerX, centerY, 5, paint);
		paint.setStrokeWidth(3);
		Calendar calendar=Calendar.getInstance();
		int currentMinute=calendar.get(Calendar.MINUTE);
		int currentHour=calendar.get(Calendar.HOUR);
		//计算分针和时针的角度
		double minuteRadin=Math.toRadians((360-((currentMinute*6)-90))%360);
		double hourRadin=Math.toRadians((360-((currentHour*30)-90))%360-(30*currentMinute/60));
		//在表盘上画分针
		canvas.drawLine(centerX, centerY, (int)(centerX+minuteSize*Math.cos(minuteRadin)), 
				(int)(centerY-hourSize*Math.sin(minuteRadin)), paint);
		paint.setStrokeWidth(4);
		paint.setColor(Color.RED);
		//画时针
		canvas.drawLine(centerX, centerY, (int)(centerX+hourSize*Math.cos(hourRadin)), 
				(int)(centerY-hourSize*Math.sin(hourRadin)), paint);
	}

}

布局文件：

<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" >

	<com.example.test.Clock 
	 android:layout_width="match_parent"
   	 android:layout_height="match_parent"
   	 clockImageSrc="@drawable/ic_launcher"
   	 scale="1.5"
   	 centerWidthScale="0.5"
   	 centerHeightScale="0.5"
   	 minuteSize="100"
   	 hourSize="30"
   	 />
</RelativeLayout>

在Activity中引用该布局文件即可显示自定义的时钟控件。