Android為開發者提供了大量的控制元件，這些控制元件只能滿足一般性的需求，有時候需要開發者重新定製控制元件。控制元件的定製有三種形式：對原有控制元件的重寫；對原有控制元件進行組合；自定義新的控制元件。Android中所有控制元件類都是View的子類。

本例主要是講一個自定義時鐘控制元件，該控制元件直接繼承View類。

1.控制元件類

首先需要編寫控制元件類，該類繼承View類，並實現介面Runnable。時鐘控制元件主要包含的引數：clockimageresourceid，scale，handcenterwidthscale，handcenterheightscale，minutehandsize，hourhandsize。

 1 public class HandClock extends View implements Runnable {
 2 
 3     private int clockImageResourceId;//影象資源id
 4     private Bitmap bitmap;//影象資源
 5     private float scale;//影象顯示的比例
 6     private float handCenterWidthScale;//橫座標顯示比例
 7     private float handCenterHeightScale;//縱座標顯示比例
 8     private int minuteHandSize;//分鐘長度
 9     private int hourHandSize;//時針長度
10     private Handler hanlder=new Handler();
11     public HandClock(Context context, AttributeSet attrs) {
12         super(context, attrs);
13         // TODO Auto-generated constructor stub
14         //讀取屬性值
15         clockImageResourceId=attrs.getAttributeResourceValue(null, "clockImageSrc", 0);
16         if(clockImageResourceId>0)
17         {
18             bitmap=BitmapFactory.decodeResource(getResources(), clockImageResourceId);
19         }
20         scale=attrs.getAttributeFloatValue(null, "scale", 1);
21         handCenterWidthScale=attrs.getAttributeFloatValue(null, "handCenterWidthScale", bitmap.getWidth()/2);
22         handCenterHeightScale=attrs.getAttributeFloatValue(null, "handCenterHeightScale", bitmap.getHeight()/2);
23         minuteHandSize=(int)(attrs.getAttributeIntValue(null, "minuteHandSize",0)*scale);
24         hourHandSize=(int)(attrs.getAttributeIntValue(null, "hourHandSize", 0)*scale);
25         int curentSecond=Calendar.getInstance().get(Calendar.SECOND);
26         hanlder.postDelayed(this, (60-curentSecond)*1000);
27     }
28 
29     protected void onDetachedFromWindow()
30     {
31         super.onDetachedFromWindow();
32         hanlder.removeCallbacks(this);
33     }
34     @Override
35     public void run() {
36         // TODO Auto-generated method stub
37         invalidate();
38         hanlder.postDelayed(this,60*1000);
39     }
40     protected void onMeasure(int widthMeasurespc,int heightMeasurespe)
41     {
42         super.onMeasure(widthMeasurespc, heightMeasurespe);
43         setMeasuredDimension((int)(bitmap.getWidth()*scale),(int)(bitmap.getHeight()*scale));
44         
45     }
46     protected void onDraw(Canvas canvas)
47     {
48         super.onDraw(canvas);
49         Paint paint=new Paint();
50         Rect src=new Rect();
51         Rect target=new Rect();
52         src.left=0;
53         src.top=0;
54         src.right=bitmap.getWidth();
55         src.bottom=bitmap.getHeight();
56         target.left=0;
57         target.top=0;
58         target.bottom=(int)(src.bottom*scale);
59         target.right=(int)(src.right*scale);
60         //畫表盤影象
61         canvas.drawBitmap(bitmap, src, target,paint);
62         //計算錶盤中心點的橫座標
63         float centerX=bitmap.getWidth()*scale*handCenterWidthScale;
64         //計算錶盤中心店的縱座標
65         float centerY=bitmap.getHeight()*scale*handCenterHeightScale;
66         
67         canvas.drawCircle(centerX, centerY, 5, paint);
68         paint.setStrokeWidth(3);
69         Calendar calendar=Calendar.getInstance();
70         int currentMin=calendar.get(Calendar.MINUTE);
71         int currentHour=calendar.get(Calendar.HOUR);
72         //計算時針和分針角度
73         double minuteRadian=Math.toRadians((360-((currentMin*6)-90))%360);
74         double hourRadian=Math.toRadians((360-((currentHour*30)-90))%360-(30*currentMin/60));
75         //畫分針
76         canvas.drawLine(centerX, centerY,(int)(centerX+minuteHandSize*Math.cos(minuteRadian)),(int)(centerY-minuteHandSize*Math.sin(minuteRadian)),paint);
77         paint.setStrokeWidth(4);
78         //畫時針
79         canvas.drawLine(centerX, centerY,(int)(centerX+hourHandSize*Math.cos(hourRadian)),(int)(centerY-hourHandSize*Math.sin(hourRadian)),paint);
80     }
81 
82 }
 

這裡面有很多重點，比如說時針與分針角度的計算，重繪的時間等。Runnable介面是軟定時器類，這裡定義一分鐘重繪一次。

2.handclok.xml

在一個xml頁面引用剛剛自定義的控制元件。

 1 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 2     android:layout_width="match_parent"
 3     android:layout_height="match_parent"
 4     android:orientation="vertical" >
 5     
 6 <com.example.myandroiddemp.HandClock
 7     android:layout_width="wrap_content"
 8     android:layout_height="wrap_content"
 9     clockImageSrc="@drawable/clock1" 
10     scale="0.7"
11     handCenterWidthScale="0.5"
12     handCenterHeightScale="0.5"
13     minuteHandSize="54"
14     hourHandSize="40"/>
15 
16 </LinearLayout>