Question

在我片段的onCreate方法中，我尝试设置ListView。问题是我写这行，

ListView listViewEmployees = (ListView) getActivity().findViewById(R.id.listViewEmployees);

并且它似乎无法找到ListView，因为它始终获取值null。

<!-- TODO: Update blank fragment layout -->
<TextView android:layout_width="match_parent" android:layout_height="match_parent"
    android:text="@string/hello_blank_fragment"
    android:id="@+id/textViewHelloEmployees" />

<ListView
    android:layout_width="wrap_content"
    android:layout_height="293dp"
    android:id="@+id/listViewEmployees"
    android:layout_gravity="center" />

片段代码：

public class FragmentEmoployees extends Fragment {
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";

// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;

private OnFragmentInteractionListener mListener;
private CollectionEmployee allEmployees;

/**
 * Use this factory method to create a new instance of
 * this fragment using the provided parameters.
 *
 * @param param1 Parameter 1.
 * @param param2 Parameter 2.
 * @return A new instance of fragment FragmentEmoployees.
 */
// TODO: Rename and change types and number of parameters
public static FragmentEmoployees newInstance(String param1, String param2) {
    FragmentEmoployees fragment = new FragmentEmoployees();
    Bundle args = new Bundle();
    args.putString(ARG_PARAM1, param1);
    args.putString(ARG_PARAM2, param2);
    fragment.setArguments(args);
    return fragment;
}

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

public FragmentEmoployees(CollectionEmployee allEmployees) {
    // Required empty public constructor
    this.allEmployees = allEmployees;
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {
        mParam1 = getArguments().getString(ARG_PARAM1);
        mParam2 = getArguments().getString(ARG_PARAM2);
    }

    ListView listViewEmployees = (ListView) getActivity().findViewById(R.id.listViewEmployees);


    System.out.println(listViewEmployees);


}

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

// TODO: Rename method, update argument and hook method into UI event
public void onButtonPressed(Uri uri) {
    if (mListener != null) {
        mListener.onFragmentInteraction(uri);
    }
}

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);

}

@Override
public void onDetach() {
    super.onDetach();
    mListener = null;
}

/**
 * This interface must be implemented by activities that contain this
 * fragment to allow an interaction in this fragment to be communicated
 * to the activity and potentially other fragments contained in that
 * activity.
 * <p/>
 * See the Android Training lesson <a href=
 * "http://developer.android.com/training/basics/fragments/communicating.html"
 * >Communicating with Other Fragments</a> for more information.
 */
public interface OnFragmentInteractionListener {
    // TODO: Update argument type and name
    public void onFragmentInteraction(Uri uri);
}

}

Answer 1

由于片段尚未显示视图，因此您无法访问onCreate()中的片段视图。片段在方法onCreateView()中获取分配给它的视图，该方法在onCreate()之后调用。您必须在onCreateView()或之后调用的方法中设置ListView。

如果您想稍后访问Fragment的视图，则必须使用getView()方法。当您在getViewById()上致电getActivity()时，它会在您的活动视图中搜索ListView，而不是片段。

Fragment里面的ListView给了我null

1 个答案: