Android片段和null对象引用

Question

I am trying to get my fragment working and I cant get it done whatever I am trying to do.

The error I am getting is:

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference

Here is the code:

public class FragmentOne extends Fragment {

    private TextView one;

    public FragmentOne() {
        // Required empty public constructor
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        one = (TextView) getActivity().findViewById(R.id.one);

        // Displaying the user details on the screen
        one.setText("kjhbguhjg");

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment1, container, false);

    }
}

Have no idea why it doesn't work. I am testing this class just to see if the text will be changed on the textview. I am using the right id because I checked that like 10 times, yet I think the problem is because textview one is a null object. But why it doesn't find the id?

Answer 1

onCreate() is called before onCreateView() and therefore you will not be able to access it in onCreate() .

Solution: Move

one = (TextView) getActivity().findViewById(R.id.one);

to onViewCreated() instead.

See picture below for an overview of the fragment lifecycle .

The new snippet looks like this:

public class FragmentOne extends Fragment {


    private TextView one;

    public FragmentOne() {
        // Required empty public constructor
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment1, container, false);
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState){
        one = (TextView) getActivity().findViewById(R.id.one);
        // Displaying the user details on the screen
        one.setText("kjhbguhjg");
    }
}

Answer 2

Or. instead of rewriting

public void onViewCreated(View view, Bundle savedInstanceState)

you can slightly change your onCreateView so it looks like

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootView = inflater.inflate(R.layout.fragment1, container, false)
one = (TextView) rootView.findViewById(R.id.one)
return rootView;
}