Android Set Text of TextView in Fragment that is in FragmentPagerAdapter

Question

This one is driving me nuts. Basically, I want to create a ViewPager and add a few Fragments to it. Then, all I want to do, it set a value in one of th

Answer 1

This line:

TextView t = (TextView) findViewById(R.id.someTextViewInFragmentA);

is looking for the view in your ParentActivity. Of course it wont find it and that's when you get your NPE.

Try something like this:

1. Add a "tag" to your fragments when you add them

2. Use someFragment = getSupportFragmentManager().findFragmentByTag("your_fragment_tag")

3. Get the view of the fragment fragmentView = someFragment.getView();

4. And finally find your TextView and set the text

   TextView t = (TextView) fragmentView.findViewById(R.id.someTextViewInFragmentA); t.setText("some text");

Answer 2

The TextView is located in the fragments layout, not in the ViewPagers or the PagerAdapter, that is causing the NPE. Now, you have 2 options.

• The first is the easiest, you should simple move your code for changing the text into the corresponding fragment's class, FragmentA in this case.

• Secondly, you could make the TextView into FragmentA static, so it can be accessed by other classes. So your code would look something like this:

   ....
   TextView myText;
  
   @Override
   public View onCreateView(....) {
  
       myLayout = ....;
  
       myText = myLayout.findViewById(yourID);
  
       ....
  }
  

And then you would change the text from somewhere else (if it's really necessary):

   FragmentA.myText.setText("new text");

Explaining method 2

Use the following in your Fragment.

public static void setText(String text) {
    TextView t = (TextView) getView().findViewById(R.id.someTextView);
    t.setText(text);
}

Then change the text like:

FragmentA.setText("Lulz");

Answer 3

Unless you are planning to change the value at runtime, you can pass the value into the fragment as a parameter. It is done my using a Bundle and passing it as args into a Fragment, which then retrieves it from it's args. More info here. If you implement this, your instantiation of new Fragments might look something like this:

public InstallAdapter(FragmentManager fm) {
            super(fm);
            FRAGMENTS = new ArrayList<Fragment>();
            FRAGMENTS.add(FragmentA.newInstance("<text to set to the TextView>"));
            FRAGMENTS.add(FragmentB.newInstance("<text to set to the TextView>"));
        }

If, however, you are planning to update the value at runtime (it will change as user is running the app), then you want to use an Interface to channell communication between your fragment and your activity. Info here. This is what it might look like:

//Declare your values for activity;
    ISetTextInFragment setText;
    ISetTextInFragment setText2;
...
//Add interface
public interface ISetTextInFragment{
    public abstract void showText(String testToShow);
}
...
//your new InstallAdapter
public InstallAdapter(FragmentManager fm) {
        super(fm);

        FRAGMENTS = new ArrayList<Fragment>();

        Fragment fragA = new FragmentA();
        setText= (ISetTextInFragment)fragA;
        FRAGMENTS.add(fragA);

        Fragment fragB = new FragmentB();
        setText2= (ISetTextInFragment)fragB;
        FRAGMENTS.add(fragB);
}

//then, you can do this from your activity:
...
setText.showText("text to show");
...

and it will update your text view in the fragment.

While it can be done "more easily", these methods are recomended because they reduce chances of bugs and make code a lot more readable and maintainable.

EDIT: this is what your Fragment should look like (modified your code):

public class FragmentA extends Fragment implements ISetTextInFragment {

    TextView myTextView;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle inState) {
        View v = inflater.inflate(R.layout.fragment_a, container, false);
        myTextView = (TextView)v.findViewbyId(R.id.someTextView)
        return v;
    }

    @Override
    public void showText(String text) {
        myTextView.setText(text);
    }
}

If after that you are still getting a null pointer exception, your TextView is NOT located where it needs to me, namely in the R.layout.fragment_a filem, and it needs to be located there. Unless you are calling the interface method BEFORE the fragment finished loading, of course.

Answer 4

How about to change this line

TextView t = (TextView) getView().findViewById(R.id.someTextView);  //UPDATE

to

TextView t = (TextView) getActivity().findViewById(R.id.someTextView);  //UPDATE

then you can try to update "t" with .setText("some_string") inside "SheetActivity".