refresh a fragment from its parent activity

问题

I have almost the exact same problem as this question here: Android, How to restart/refresh a fragment from FragmentActivty?

I'm trying to call the a method of a ListFragment from the parent FragmentActivity.

However, I'm using the template Swipe + Fixed Tabs generated by eclipse. I tried calling getSupportFragmentManager().findFragmentById(R.id.myfragment) but the return value is always null. I'm guessing this might be a problem because I did not define myfragment anywhere in my app. But I am unsure where to define it as all fragments are created dynamically.

For those who are not familiar with the Swipe + Fixed Tabs template generated by the Android SDK in Eclipse, the fragments are created by overriding the FragmentPagerAdapter getItem function, returning a new instance of my fragment.

Any help would be appreciated.

Relevant code: How I setup my adapter:

mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

// Set up the ViewPager with the sections adapter.
mViewPager = (ViewPager) findViewById(R.id.activity_comment);
mViewPager.setAdapter(mSectionsPagerAdapter);

Overriding the adapter getItem function:

@Override
    public Fragment getItem(int position) {
        // getItem is called to instantiate the fragment for the given page.
        // Return a DummySectionFragment (defined as a static inner class
        // below) with the page number as its lone argument.

        switch(position) {
        case 0:
            return CommentsFragment.newInstance();

        case 1:
        default:
            return LikesFragment.newInstance();
        }
    }

The newInstance() functions simply return an instance of themselves, since the classes for my fragment are static.

回答1:

You can find your fragment by the Tag, but of course you need to give this tag to it while adding the fragment.

First add your fragment with a tag:

        fragmentManager = getFragmentManager();
        fragmentTransaction = fragmentManager.beginTransaction();
        SomeFragment fragment = new ManageLinksFragment();
        fragmentTransaction.add(R.id.fragment_container1,fragment, "sometag");
        fragmentTransaction.commit();

And then on the Activity's site:

SomeFragment mSomeFragment = (SomeFragment) getFragmentManager().findFragmentByTag("sometag");
// now mSomeFragment.callsomething();

回答2:

You have to do this :

frag.getFragmentManager().beginTransaction().detach(frag).commit();
frag.getFragmentManager().beginTransaction().attach(frag).commit();

回答3:

Your fragments are managed by the adapter. Therefore, you also have to call for the adapter to refresh your fragments. These steps are necessary:

Override getItemPosition in your Adapter

@Override
public int getItemPosition(Object object) {
    // POSITION_NONE makes it possible to reload the PagerAdapter
    return POSITION_NONE;
}

Once you did that call
```
mViewPager.getAdapter.notifyDataSetChanged();
```
in your Activity. From the fragment object itself you could use a callback to inform the Activity of the need to refresh.

This will freshly populate the viewPager with new instances of your fragments which is like restarting / refreshing the fragment.

Hope it helps and this was what you were looking for.