在ViewPager中更改片段的文本

Question

@Override
public Fragment getItem(int position) {
    CharacterFragment fragment = new CharacterFragment();
    View rootView = fragment.getView();
    TextView character = (TextView) rootView.findViewById(R.id.character);
    character.setText(name[position]);
    return fragment;
}  

This is my code for changing the fragment in the ViewPager . The fragment just has a single text view. basically, I am just siwping through the alphabets in my name. So, depending on the index, I have to set the text in the TextView of the fragment.

With the above code, the programs blows with a NullPointerException because the layout has not been inflated yet, so I presume.

What would be the right way to change the content of the Fragment ? Is there a callback method that would let me know that it has become visible ?

Answer 1

There is no callback. You could send the text as a parameter to the fragment when you're creating it and set the text inside of the fragment.

Something like:

@Override
public Fragment getItem(int position) {
    CharacterFragment fragment = CharacterFragment.newInstance(name[position]);
    View rootView = fragment.getView();
    return fragment;
}

your CharacterFragment.newInstance(String name) method would look like:

public static CharacterFragment.newInstance(String name) {
    CharacterFragment fragment = new CharacterFragment();
    Bundle args = new Bundle();
    args.put("NAME_ARG", name);
    fragment.setArguments(args);
    return fragment;
}

then in your onCreateView() you get the arguments through getArguments() method and you get the string with key NAME_ARG . And you have it! Makes sense?

Answer 2

That's not the correct way to use getView() . The way to accomplish what you want is a little different. In order to do so you should pass the string (in this case name[position] ) to the method. But you should remember that Fragments are not supposed to be instantiated with their constructor, instead create a static method, I'll show you:

@Override
public Fragment getItem(int position) {
    CharacterFragment fragment = CharacterFragment.newInstance(name[position]);
    return fragment;
}  

And then, inside CharacterFragment.java

public static CharacterFragment newInstance(String name) {
    Bundle bundle = new Bundle();
    bundle.putString("key_name",name);

    CharacterFragment fragment = new CharacterFragment();
    CharacterFragment.setsetArguments(bundle);

    return fragment;
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {

     View view = inflater.inflate(R.layout.fragment_xml_file, container, false);

     // AND HERE WE GO
     String name = getArguments().getString("key_name");
     TextView character= view.findViewById(R.id.character);
     character.setText(name);

     return view;
}