实习入职第二天：onAttachedToWindow () 和 onDetachedFromWindow ()

在重写View的时候，会遇到这两个方法

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

当此view附加到窗体上时调用该方法。在这时，view有了一个用于显示的Surface，将开始绘制。注意，此方法要保证在调用onDraw(Canvas) 之前调用，但可能在调用 onDraw(Canvas) 之前的任何时刻，包括调用 onMeasure(int, int)之前或之后。

看得出次方法在onDraw方法之前调用，也就是view还没有画出来的时候，可以在此方法中去执行一些初始化的操作，google的AlarmClock动态时钟View就是在这个方法中进行广播的注册，代码如下：

 @Override
     protected void onAttachedToWindow() {
         super.onAttachedToWindow();

         if (Log.LOGV) Log.v("onAttachedToWindow " + this);

         if (mAttached) return;
         mAttached = true;

         if (mAnimate) {
             setBackgroundResource(R.drawable.animate_circle);
             /* Start the animation (looped playback by default). */
             ((AnimationDrawable) getBackground()).start();
         }

         if (mLive) {
             /* monitor time ticks, time changed, timezone */
             IntentFilter filter = new IntentFilter();
             filter.addAction(Intent.ACTION_TIME_TICK);
             filter.addAction(Intent.ACTION_TIME_CHANGED);
             filter.addAction(Intent.ACTION_TIMEZONE_CHANGED);
             mContext.registerReceiver(mIntentReceiver, filter, null, mHandler);
         }

         /* monitor 12/24-hour display preference */
         mFormatChangeObserver = new FormatChangeObserver();
         mContext.getContentResolver().registerContentObserver(
                 Settings.System.CONTENT_URI, true, mFormatChangeObserver);

         updateTime();
     }

另外在屏蔽Home键的时候也会用到

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

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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>

将视图从窗体上分离的时候调用该方法。这时视图已经不具有可绘制部分。

 

onDetachedFromWindow()正好与onAttachedToWindow()的用法相对应，在destroy view的时候调用，所以可以加入取消广播注册等的操作，还是google的闹钟代码：

 @Override
     protected void onDetachedFromWindow() {
         super.onDetachedFromWindow();

         if (!mAttached) return;
         mAttached = false;

         Drawable background = getBackground();
         if (background instanceof AnimationDrawable) {
             ((AnimationDrawable) background).stop();
         }

         if (mLive) {
             mContext.unregisterReceiver(mIntentReceiver);
         }
         mContext.getContentResolver().unregisterContentObserver(
                 mFormatChangeObserver);
     }

具体的用法视个人的需求而定了，自己控制重写就好了。