Android重写view时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：

[java]
view plaincopyprint?

@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();
}

@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

[java]
view plaincopyprint?

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

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

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

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：

[java]
view plaincopyprint?

@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); }

@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。