//step2:Activity被系统回收时,会主动调用onSaveInstance()方法来保存视图层(View Hierarchy),然后通过onRestoreInstanceState()方法来恢复视图层.(activity中两个方法的核心代码如下)
//step3:所以当Activity通过导航再次被重建时,之前被实例化过的Fragment依然会出现在Activity中
protected void onRestoreInstanceState(Bundle savedInstanceState) {
if (mWindow != null) {
//取出视图层
Bundle windowState = savedInstanceState.getBundle(WINDOW_HIERARCHY_TAG);
if (windowState != null) {
mWindow.restoreHierarchyState(windowState);
}
}
}
protected void onSaveInstanceState(Bundle outState) {
//保存视图层
outState.putBundle(WINDOW_HIERARCHY_TAG, mWindow.saveHierarchyState());
Parcelable p = mFragments.saveAllState();
if (p != null) {
outState.putParcelable(FRAGMENTS_TAG, p);
}
getApplication().dispatchActivitySaveInstanceState(this, outState);
}
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