Getting reference to nested fragment from FragmentTabHost

问题

In my application, I use an Activity which holds one Fragment with FragmentTabHost and hence all its tabs are nested Fragments.

Inside an Activity which holds a Fragment with its nested Fragment, we may get a reference to attached one using onAttachedFragment().

But how to get a reference to nested Fragment from FragmentTabHost?

回答1:

Well, exploring the source code of FragmentTabHost I've found that when it adds a fragment tab, it assignes a tag of TabSpec to nested Fragment.

So to get the reference to this Fragment we should call

getChildFragmentManager().findFragmentByTag(tabSpecTag)

回答2:

I was trying this for a while, but I was getting null returned from the FragmentManager because I was trying to access the manager in onCreateView() immediately after adding.

Here is a good explanation on what happened

It's also important to note that Fragment tabs that have not yet been selected don't exist yet in the FragmentManager, and so will return null as well. I got around this by calling mTabHost.setCurrentTab(index) before trying get to the Fragment with the FragmentManager. It's not very clean, but it works.

回答3:

Above solutions are also working but I have one more easy solution,

 @Override
public void onTabChanged(final String tabId) {

    new Handler().postDelayed(new Runnable() {
        @Override
        public void run() {

            mFragment = getChildFragmentManager().findFragmentByTag("Tagname");
        }
    },1000);
}

Here you have to implement FragmentTabHost.onTabChangeListener We have kept a second delay in fetching fragment from the childFragmentManager.

Note : You need to cast mFragment which fragment you have used.

回答4:

I found a solution that I like a little better because it doesn't involving executing code with a delay (which is always iffy given android hardware fragmentation and different processor speeds).

In your onTabChanged() method, before you try to find the fragment, call executePendingTransactions() on the fragment manager associated with your tabHost. It seems there are some places in the FragmentTabHost source code where they should be calling executePendingTransactions() but fail to do so.

This works every time the tab changes with one exception... the first tab that is selected still comes back null... In my specific case, I was able to handle this exception differently anyway, by putting some code in onResume.

Hope this helps.

来源：https://stackoverflow.com/questions/15898233/getting-reference-to-nested-fragment-from-fragmenttabhost