Android -- onAttachedToWindow()

標籤：

onAttachedToWindow在Activity生命週期中的位置

放大招：

onAttachedToWindow不能在onCreate中喲~

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中進行測試，結果在lp.gravity = Gravity.CENTER;這行報了null 指標異常，所以view.getLayoutParams()擷取的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);                    }                }                     ......            }                ......        }              ......    }

原來在ActivityThread執行handleResumeActivity時就會為PhoneWindow（r.activity.getWindow）中的DecorView設定LayoutParam，並且通過源碼發現handleResumeActivity函數首先會執行performResumeActivity，此時會調用Activity的onResume()生命週期函數，這時問題就比較清晰了，看來只要在Activity的onResume生命週期後就能擷取DecorView的LayoutParam，進而可以設定高度和寬度了。根據上面貼出的生命週期圖，onResume()後面是onAttachedToWindow()，並且onAttachedToWindow只會調用一次，不會受使用者操作行為影響。所以在onAttachedToWindow中進行視窗尺寸的修改再合適不過了。

乾貨

• onAttachedToWindow運行在onResume之後；
• DecorView的LayoutParams是在ActivityThread的handleResumeActivity中設定的，並且該函數會調用Activity的onResume生命週期，所以在onResume之後可以設定表單尺寸；

我是天王蓋地虎的分割線

 

 

參考：http://blog.csdn.net/guxiao1201/article/details/41517871

Android -- onAttachedToWindow()