Android重寫view時onAttachedToWindow () 和 onDetachedFromWindow ()

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       在重寫View的時候，會遇到這兩個方法

protected void onAttachedToWindow()

Description copied from class: View

This is called when the view is attached to a window. At this point it has a Surface and will start drawing. Note that this function is guaranteed to be called before View.onDraw(Android.graphics.Canvas), however it may be called any time before the first onDraw -- including before or after View.onMeasure(int, int).
Overrides:
onAttachedToWindow in class View

當此view附加到表單上時調用該方法。在這時，view有了一個用於顯示的Surface，將開始繪製。注意，此方法要保證在調用onDraw(Canvas)之前調用，但可能在調用 onDraw(Canvas) 之前的任何時刻，包括調用 onMeasure(int, int)之前或之後。

看得出次方法在onDraw方法之前調用，也就是view還沒有畫出來的時候，可以在此方法中去執行一些初始化的操作，google的AlarmClock動態時鐘View就是在這個方法中進行廣播的註冊，代碼如下：

[java] view plain copy

1. @Override  
2.     protected void onAttachedToWindow() {  
3.         super.onAttachedToWindow();  
4.   
5.         if (Log.LOGV) Log.v("onAttachedToWindow " + this);  
6.   
7.         if (mAttached) return;  
8.         mAttached = true;  
9.   
10.         if (mAnimate) {  
11.             setBackgroundResource(R.drawable.animate_circle);  
12.             /* Start the animation (looped playback by default). */  
13.             ((AnimationDrawable) getBackground()).start();  
14.         }  
15.   
16.         if (mLive) {  
17.             /* monitor time ticks, time changed, timezone */  
18.             IntentFilter filter = new IntentFilter();  
19.             filter.addAction(Intent.ACTION_TIME_TICK);  
20.             filter.addAction(Intent.ACTION_TIME_CHANGED);  
21.             filter.addAction(Intent.ACTION_TIMEZONE_CHANGED);  
22.             mContext.registerReceiver(mIntentReceiver, filter, null, mHandler);  
23.         }  
24.   
25.         /* monitor 12/24-hour display preference */  
26.         mFormatChangeObserver = new FormatChangeObserver();  
27.         mContext.getContentResolver().registerContentObserver(  
28.                 Settings.System.CONTENT_URI, true, mFormatChangeObserver);  
29.   
30.         updateTime();  
31.     }  

另外在屏蔽Home鍵的時候也會用到

[java] view plain copy

1. public void onAttachedToWindow() {  
2. this.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD);  
3. super.onAttachedToWindow();  
4. }  

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

 

protected void onDetachedFromWindow()

Description copied from class: View
This is called when the view is detached from a window. At this point it no longer has a surface for drawing.
Overrides:
onDetachedFromWindow in class AdapterView<ListAdapter>

將視圖從表單上分離的時候調用該方法。這時視圖已經不具有可繪製部分。

 

onDetachedFromWindow()正好與onAttachedToWindow()的用法相對應，在destroy view的時候調用，所以可以加入取消廣播註冊等的操作，還是google的鬧鐘代碼：

[java] view plain copy

1. @Override  
2.     protected void onDetachedFromWindow() {  
3.         super.onDetachedFromWindow();  
4.   
5.         if (!mAttached) return;  
6.         mAttached = false;  
7.   
8.         Drawable background = getBackground();  
9.         if (background instanceof AnimationDrawable) {  
10.             ((AnimationDrawable) background).stop();  
11.         }  
12.   
13.         if (mLive) {  
14.             mContext.unregisterReceiver(mIntentReceiver);  
15.         }  
16.         mContext.getContentResolver().unregisterContentObserver(  
17.                 mFormatChangeObserver);  
18.     }  

具體的用法視個人的需求而定了，自己控制重寫就好了。

Android重寫view時onAttachedToWindow () 和 onDetachedFromWindow ()