Question

我使用以下片段来显示注释列表，但是当我从同一活动中的另一个片段进入此处时，它会将db中相同的值再次放入列表中。我怎样才能避免这种情况发生？

import android.app.Activity;
import android.database.Cursor;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AdapterView;
import android.widget.ListAdapter;
import android.widget.TextView;


import com.frisodenijs.allinoneorganiser.dummy.DummyContent;

import java.util.ArrayList;
import java.util.List;

/**
 * A fragment representing a list of Items.
 * <p/>
 * Large screen devices (such as tablets) are supported by replacing the ListView
 * with a GridView.
 * <p/>
 * Activities containing this fragment MUST implement the {@link OnFragmentInteractionListener}
 * interface.
 */
public class NotesFragment extends Fragment implements AbsListView.OnItemClickListener {

    private List notesList;

    // 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;

    /**
     * The fragment's ListView/GridView.
     */
    private AbsListView mListView;

    /**
     * The Adapter which will be used to populate the ListView/GridView with
     * Views.
     */
    private ListAdapter mAdapter;

    // TODO: Rename and change types of parameters
    public static NotesFragment newInstance(String param1, String param2) {
        NotesFragment fragment = new NotesFragment();
        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 NotesFragment() {
    }

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

        notesList = new ArrayList();

        DummyContent.getInstance(getActivity()).noteDummies();

        // TODO: Change Adapter to display your content
        mAdapter = new NotesAdapter(getActivity(), notesList);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_notes, container, false);

        // Set the adapter
        mListView = (AbsListView) view.findViewById(android.R.id.list);
        ((AdapterView<ListAdapter>) mListView).setAdapter(mAdapter);

        // Set OnItemClickListener so we can be notified on item clicks
        mListView.setOnItemClickListener(this);

        return view;
    }

    @Override
    public void onResume() {
        super.onResume();

        DBAdapter db = new DBAdapter(getActivity());
        db.open();

        Cursor c = db.getAllNotes();
        if (c.moveToLast()) {
            do {
                notesList.add(new Note(Long.parseLong(c.getString(0)), c.getString(1)));
            }while (c.moveToPrevious());
        }

        db.close();
    }

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

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


    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        Note note = (Note) this.notesList.get(position);
        //Toast.makeText(getActivity(), note.getText() + "Clicked!", Toast.LENGTH_SHORT).show();
/*
        FragmentTransaction transaction = getActivity().getSupportFragmentManager().beginTransaction();
        transaction.replace(R.id.container_notes_fragment, new NotesEditFragment());
        transaction.addToBackStack(null);
        transaction.commit();
*/
        mListener.goToNotesEditFragment(note);

        //if (null != mListener) {
            // Notify the active callbacks interface (the activity, if the
            // fragment is attached to one) that an item has been selected.
          //  mListener.onFragmentInteraction(DummyContent.ITEMS.get(position).id);
     //   }
    }

    /**
     * The default content for this Fragment has a TextView that is shown when
     * the list is empty. If you would like to change the text, call this method
     * to supply the text it should use.
     */
    public void setEmptyText(CharSequence emptyText) {
        View emptyView = mListView.getEmptyView();

        if (emptyView instanceof TextView) {
            ((TextView) emptyView).setText(emptyText);
        }
    }

    /**
     * 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 {
        public void goToNotesEditFragment(Note note);
    }

}

Answer 1

您可以将所需的所有值从一个片段传递到另一个片段，这样您就不必再次将它们从db中传出。

请注意：不鼓励两个片段之间的直接通信，您应该创建一个回调给您的活动的电话，并从那里将数据传递给另一个片段。（你可以使用

setArguments()

）

如何避免将游标副本添加到android中的列表？

1 个答案: