Fragments - kgleong/software-engineering GitHub Wiki
Fragment#onSaveInstanceState() is called whenever Activity#onSaveInstanceState() is called.
Here's a look at the call chain:
In FragmentActivity, which is the support library base activity class:
- any call to
onSaveInstanceState()triggers a call to the activity's fragment manager to save the state for all of the fragments in this activity.
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
// mFragments is the fragment manager for this activity
// saveAllState() saves the state for all fragments in this activity.
Parcelable p = mFragments.saveAllState();
if (p != null) {
outState.putParcelable(FRAGMENTS_TAG, p);
}
}In FragmentManagerImpl, which is the concrete FragmentManager class that manages fragments for all FragmentActivity instances:
- It's important to note that every fragment manager has a
mActivefield that is of typeArrayList<Fragment>.- This is a list of all fragments in the associated activity. A fragment manager is associated with only a single activity.
Parcelable saveAllState() {
...
// mActive is a list of all fragments in this activity.
for (int i = 0; i < mActive.size(); i++) {
Fragment f = mActive.get(i);
if (f != null) {
...
// This constructor never sets mSavedFragmentState.
FragmentState fs = new FragmentState(f);
...
// All fragments start in the INITIALIZING state and don't stay
// here for very long unless they're about to be detached/destroyed
if (f.mState > Fragment.INITIALIZING && fs.mSavedFragmentState == null) {
// saveFragmentBasicState() calls f.onSaveInstanceState()
fs.mSavedFragmentState = saveFragmentBasicState(f);
...
}
}
}
...
}
Bundle saveFragmentBasicState(Fragment f) {
...
// This is what calls fragment#onSaveInstanceState()
f.performSaveInstanceState(mStateBundle);
...
}