Android -- onAttachedToWindow()

浏览数：74 / 时间：2015年06月11日

onAttachedToWindow在Activity生命周期中的位置

放大招：

onAttachedToWindow不能在onCreate中哟~

View view = getWindow().getDecorView();  
WindowManager.LayoutParams lp = (WindowManager.LayoutParams)view.getLayoutParams();  
lp.gravity = Gravity.CENTER;  
lp.width = (dm.widthPixels * 4) / 5;  
lp.height = (dm.widthPixels * 4) / 5;  
getWindowManager().updateViewLayout(view,lp);

放到onCreate中进行测试，结果在lp.gravity = Gravity.CENTER;这行报了空指针异常，所以view.getLayoutParams()获取的LayoutParams是空。

public final class ActivityThread {    
    ......    
    
    final void handleResumeActivity(IBinder token, boolean clearHide, boolean isForward) {    
        ......    
    
        ActivityClientRecord r = performResumeActivity(token, clearHide);    
    
        if (r != null) {    
            final Activity a = r.activity;    
            ......    
    
            // If the window hasn‘t yet been added to the window manager,    
            // and this guy didn‘t finish itself or start another activity,    
            // then go ahead and add the window.    
            boolean willBeVisible = !a.mStartedActivity;    
            if (!willBeVisible) {    
                try {    
                    willBeVisible = ActivityManagerNative.getDefault().willActivityBeVisible(    
                            a.getActivityToken());    
                } catch (RemoteException e) {    
                }    
            }    
            if (r.window == null && !a.mFinished && willBeVisible) {    
                r.window = r.activity.getWindow();    
                View decor = r.window.getDecorView();    
                decor.setVisibility(View.INVISIBLE);    
                ViewManager wm = a.getWindowManager();    
                WindowManager.LayoutParams l = r.window.getAttributes();    
                a.mDecor = decor;    
                l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;    
                ......    
                if (a.mVisibleFromClient) {    
                    a.mWindowAdded = true;    
                    wm.addView(decor, l);    
                }    
            }     
    
            ......    
        }    
    
        ......    
    }    
      
    ......    
}

原来在ActivityThread执行handleResumeActivity时就会为PhoneWindow（r.activity.getWindow）中的DecorView设置LayoutParam，并且通过源码发现handleResumeActivity函数首先会执行performResumeActivity，此时会调用Activity的onResume()生命周期函数，这时问题就比较清晰了，看来只要在Activity的onResume生命周期后就能获取DecorView的LayoutParam，进而可以设置高度和宽度了。根据上面贴出的生命周期图，onResume()后面是onAttachedToWindow()，并且onAttachedToWindow只会调用一次，不会受用户操作行为影响。所以在onAttachedToWindow中进行窗口尺寸的修改再合适不过了。