重写view的onAttachedToWindow () 和 onDetachedFromWindow ()与Home键屏蔽，捕获，修改

转自： http://blog.csdn.net/heng615975867/article/details/17045071
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
plaincopy

@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
plaincopy

public void onAttachedToWindow() {

this.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD);

super.onAttachedToWindow();

}

在Level5以上(包含)中，Activity类中有如下方法: public void onAttachedToWindow () Since: API Level 5 Called when the main wi ...

开发过程中相信大家都有碰到因为不能捕获Home键而烦恼，现在终于有办法了，在Level5以上(包含)中，Activity类中有如下方法：

[java] view
plaincopy





public void onAttachedToWindow ()

Since: API Level 5

Called when the main window associated with the activity has been attached to the window manager. See View.onAttachedToWindow() for more information.

See Also

* onAttachedToWindow()

private boolean catchHomeKey = false;

@Override

public void onAttachedToWindow() {

// TODO Auto-generated method stub

if(catchHomeKey) {

this.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD);

}

super.onAttachedToWindow();

}

@Override

public boolean onKeyDown(int keyCode, KeyEvent event) {

// TODO Auto-generated method stub

if(keyCode == KeyEvent.KEYCODE_HOME) {

Log.e(TAG, "Home key down");

}

return super.onKeyDown(keyCode, event);

}

重写Activity中的onAttachedToWindow方法，设置Type，就能捕获到Home键。

当不需要捕获时，删除setType这一行就OK。

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

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
plaincopy

@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);

}

关于在Activity中什么时候调用onAttachedToWindow()和onDetachedFromWindow()，我通常测试打了下log，发现onAttachedToWindow()在onResume()之后运行，onDetachedFromWindow()则在onDestory()之后才会调用。

=========================================================================================================

更新视图的函数onDraw()和dispatchdraw()的区别

绘制VIew本身的内容，通过调用View.onDraw(canvas)函数实现

绘制自己的孩子通过dispatchDraw（canvas）实现

View组件的绘制会调用draw(Canvas canvas)方法，draw过程中主要是先画Drawable背景，对 drawable调用setBounds()，然后是draw(Canvas c)方法。有点注意的是背景drawable的实际大小会影响view组件的大小，drawable的实际大小通过getIntrinsicWidth()和getIntrinsicHeight()获取，当背景比较大时view组件大小等于背景drawable的大小。

画完背景后，draw过程会调用onDraw(Canvas canvas)方法，然后就是dispatchDraw(Canvas canvas)方法，dispatchDraw()主要是分发给子组件进行绘制，我们通常定制组件的时候重写的是onDraw()方法。值得注意的是ViewGroup容器组件的绘制，当它没有背景时直接调用的是dispatchDraw()方法,
而绕过了draw()方法，当它有背景的时候就调用draw()方法，而draw()方法里包含了dispatchDraw()方法的调用。因此要在ViewGroup上绘制东西的时候往往重写的是dispatchDraw()方法而不是onDraw()方法，或者自定制一个Drawable，重写它的draw(Canvas c)和 getIntrinsicWidth()，getIntrinsicHeight()方法，然后设为背景