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：

@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

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。