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。