java - 如何查询 CursorLoader？

Question

正在寻找在 CursorLoader 上查询(或执行搜索功能)的简单方法...我尝试了 SearchView 并且可以加载数据，但是一旦我尝试搜索，应用程序就会崩溃。 .有什么想法吗？

package com.example.studentapp.activity;

import android.app.LoaderManager;
import android.content.ContentUris;
import android.content.CursorLoader;
import android.content.Intent;
import android.content.Loader;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.v4.app.NavUtils;
import android.support.v7.app.AppCompatActivity;
import android.text.TextUtils;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.SearchView;
import android.widget.SearchView.OnQueryTextListener;

import com.example.studentapp.R;
import com.example.studentapp.adapter.MentorAdapter;
import com.example.studentapp.data.Contract.MentorEntry;

public class Mentors extends AppCompatActivity implements LoaderManager.LoaderCallbacks<Cursor>, OnQueryTextListener {

    private static final int MENTOR_LOADER = 0;
    String cursorFilter;
    private MentorAdapter mMentorAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.mentors);

        ListView mentorListView = findViewById(R.id.list);

        mMentorAdapter = new MentorAdapter(this, null);

        mentorListView.setAdapter(mMentorAdapter);

        View emptyView = findViewById(R.id.empty_view);
        mentorListView.setEmptyView(emptyView);

        mentorListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Intent intent = new Intent(Mentors.this, MentorInfo.class);
                Uri currentMentor = ContentUris.withAppendedId(MentorEntry.CONTENT_URI, id);

                intent.setData(currentMentor);

                startActivity(intent);
            }
        });

        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(Mentors.this, MentorInfo.class);
                startActivity(intent);
            }
        });

        getLoaderManager().initLoader(MENTOR_LOADER, null, this);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.list_menu, menu);

        MenuItem item = menu.add("Search");
        item.setIcon(android.R.drawable.ic_menu_search);
        item.setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM);
        SearchView searchView = new SearchView(Mentors.this);
        searchView.setOnQueryTextListener(this);
        item.setActionView(searchView);

        return true;
    }

    @Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        super.onPrepareOptionsMenu(menu);

        MenuItem menuItem = menu.findItem(R.id.action_delete);
        menuItem.setVisible(false);

        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.action_save:
                return true;
            case R.id.action_delete:
                return true;
            case android.R.id.home:
                NavUtils.navigateUpFromSameTask(this);
                return true;
        }
        return super.onOptionsItemSelected(item);
    }

    @Override
    public Loader<Cursor> onCreateLoader(int arg0, Bundle arg1) {
        Uri baseUri;
        if (cursorFilter != null) {
            baseUri = Uri.withAppendedPath(MentorEntry.CONTENT_URI,
                    Uri.encode(cursorFilter));
        } else {
            baseUri = MentorEntry.CONTENT_URI;
        }

        String select = "((" + MentorEntry.COLUMN_NAME + " NOTNULL) AND ("
                + MentorEntry.COLUMN_NAME + " != '' ))";

        String[] projection = new String[] {
                MentorEntry._ID,
                MentorEntry.COLUMN_NAME,
                MentorEntry.COLUMN_EMAIL,
        };

        CursorLoader cursorLoader = new CursorLoader(
                Mentors.this,
                baseUri,
                projection,
                select,
                null,
                MentorEntry.COLUMN_NAME);

        return cursorLoader;
    }

    @Override
    public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
        mMentorAdapter.swapCursor(data);
    }

    @Override
    public void onLoaderReset(Loader<Cursor> loader) {
        mMentorAdapter.swapCursor(null);
    }

    @Override
    public boolean onQueryTextSubmit(String query) {
        return false;
    }

    @Override
    public boolean onQueryTextChange(String arg0) {
        cursorFilter = !TextUtils.isEmpty(arg0) ? arg0 : null;
        getLoaderManager().restartLoader(MENTOR_LOADER, null, this);
        return true;
    }
}

Answer 1

我发现了……我们的做法是错误的!这是有效的:

@Override
    public Loader<Cursor> onCreateLoader(int id, Bundle args) {

        String select;
        if (cursorFilter != null) {
            select = MentorEntry.COLUMN_NAME +" like '%" + cursorFilter + "%'";
        } else {
            select = null;
        }

        String[] projection = {
                MentorEntry._ID,
                MentorEntry.COLUMN_NAME,
                MentorEntry.COLUMN_EMAIL
        };

        return new CursorLoader(this, MentorEntry.CONTENT_URI, projection, select,
                null, MentorEntry.COLUMN_NAME);
    }