GetTag () always returns null when called in a fragment

Question

I have a problem because the getTag () method returns me null when I call it in a fragment that is part of the layout of the ViewPager tab you created.

The code

import java.util.ArrayList; import android.os.Bundle; import android.support.v4.app.Fragment; import android.support.v4.app.FragmentTransaction; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.ListView; import android.widget.Toast; public class HistoryFragment extends Fragment { ListView listView; HistoryAdapter adapter; @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View history = inflater.inflate(R.layout.fragment_history, container, false); ArrayList<ToSave> arrayOfData = new ArrayList<ToSave>(); adapter = new HistoryAdapter(getActivity().getBaseContext(), arrayOfData); listView = (ListView) history.findViewById (R.id.listView1); listView.setAdapter(adapter); String myTag = getTag(); ((MainActivity)getActivity()).setHistoryFragment(myTag); Toast.makeText(getActivity(), "HistoryFragment.onCreateView(): " + myTag, Toast.LENGTH_LONG).show(); return history; } } 

I want to use it to communicate between fragments (add ListView items by clicking a button in another fragment), but I cannot get it to work.

change

TabPagerAdapter.java

  @Override public Fragment getItem(int i) { switch (i) { case 0: if (mFragmentAtPos0 ==null) { mFragmentAtPos0 = new PartyFragment(listener); } return mFragmentAtPos0; case 1: return new SummaryFragment(); case 2: return new HistoryFragment(); } return null; } 

Answer 1

Tags

Fragment not specified automatically. You must assign them yourself. There are several places for this, depending on how you attach the fragment: in XML or dynamically.

If it is specified in XML, you can install it as follows:

 <fragment android:name="com.example.news.ArticleListFragment" android:id="@+id/list" android:tag="your_tag" android:layout_weight="1" android:layout_width="0dp" android:layout_height="match_parent" /> 

If you add a fragment dynamically, you can do it as follows:

 ExampleFragment fragment = new ExampleFragment(); fragmentTransaction.add(R.id.fragment_container, fragment, "your_tag"); fragmentTransaction.commit(); 

In both examples, find "your_tag" .

Then, when you call getTag() on you Fragment , you will get the result "your_tag" .

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When using your FragmentPagerAdapter fragments, tags are automatically assigned based on getItemId(int) , which by default returns the position of the pager. Therefore, the call to getTag() will return the position of the fragment in the ViewPager .

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If you use FragmentStatePagerAdapter tags, NOT . If in this case you need to switch to the first type of adapter or use a different method to link to your fragments.

From the adapter implementation, I know that you have only 3 pages, so the FragmentPagerAdapter more suitable for you.

As evidence, this is part of the description from the FragmentStatePagerAdapter :

This version of the pager is more useful when there are a large number of pages that look more like a list view.

and the following description from the FragmentPagerAdapter :

This version of the pager is best used when there are several usually more static fragments that should be unloaded, for example, a set of Tabs.

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If you insist on using the FragmentStatePagerAdapter, read on:

I guess you need tags in order to find your snippets later. Instead, the tags retain the link to the snippet. Your activity method ((MainActivity)getActivity()).setHistoryFragment(myTag); already expecting a fragment of a certain type. So you can call it this way: ((MainActivity)getActivity()).setHistoryFragment(this); Later, instead of searching for a fragment, check to see if it is null and use it.