Android - 从 Activity 启动 Fragment

Question

我正在尝试从 Activity 启动片段（列表视图）。 当单击按钮时，开关应该启动。

我的Activity从Activity扩展，Fragment扩展ListFragment。

我试过了

FragmentManager fragmentManager  = getFragmentManager();
FragmentTransaction transaction = fragmentManager.beginTransaction();
AusgabenFragment ausgabenFragment = new AusgabenFragment();
transaction.replace(R.id.contentFragment, ausgabenFragment);
transaction.commit();

和

Intent intent;
intent = new Intent(getApplicationContext(), AusgabenFragment.class);
startActivity(intent);

意图尝试的错误：

找不到明确的活动类

我知道我不必将 Fragments 添加到 AndroidManifest

感谢大家的建议

编辑：待启动片段源

public class AusgabenFragment extends ListFragment {

// 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 OnAusgabenInteractionListener mListener;

// TODO: Rename and change types of parameters
public static AusgabenFragment newInstance(String param1, String param2) {
    AusgabenFragment fragment = new AusgabenFragment();
    Bundle args = new Bundle();
    args.putString(ARG_PARAM1, param1);
    args.putString(ARG_PARAM2, param2);
    fragment.setArguments(args);
    return fragment;
}

/**
 * Mandatory empty constructor for the fragment manager to instantiate the
 * fragment (e.g. upon screen orientation changes).
 */
public AusgabenFragment() {
}

private AusgabenDataSource dataSource;

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

    if (getArguments() != null) {
        mParam1 = getArguments().getString(ARG_PARAM1);
        mParam2 = getArguments().getString(ARG_PARAM2);
    }
}

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

    dataSource = new AusgabenDataSource(getActivity()); // context mit getActivity
    try {
        dataSource.open();  // kann Exception werfen daher try catch
    } catch (SQLException e) {
        e.printStackTrace();
    }
    List<Ausgaben> AusgabenList = dataSource.getAllAusgaben();
    setListAdapter(new ArrayAdapter<Ausgaben>(getActivity(),
            android.R.layout.simple_list_item_1, android.R.id.text1, AusgabenList));
}

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    try {
        mListener = (OnAusgabenInteractionListener) activity;
    } catch (ClassCastException e) {
        throw new ClassCastException(activity.toString()
                + " must implement OnFragmentInteractionListener");
    }
}

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


@Override
public void onListItemClick(ListView l, View v, int position, long id) {
    super.onListItemClick(l, v, position, id);

    Intent intent = new Intent(getActivity(),AusgabenDetailsActivity.class);
    String Titel = l.getItemAtPosition(position).toString();
    intent.putExtra("value_title",Titel);
    getActivity().startActivity(intent);


    if (null != mListener) {
        // Notify the active callbacks interface (the activity, if the
        // fragment is attached to one) that an item has been selected.

    }
}

public interface OnAusgabenInteractionListener {
    // TODO: Update argument type and name
    public void onAusgabenInteraction(String id);
}

}

Answer 1

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    try {
        mListener = (OnAusgabenInteractionListener) activity;
    } catch (ClassCastException e) {
        throw new ClassCastException(activity.toString()
                + " must implement OnFragmentInteractionListener");
    }
}

此代码期望托管片段的活动实现OnAusgabenInteractionListener。然后它会抛出一个不正确的异常，让你更加困惑。

如果您想使用代码，您的活动将需要实现OnAusgabenInteractionListener，无论是什么。