loader的简单使用过程分析

首先，fragment或者activity必须实现callback接口

必须实现的三个方法为

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

public void onLoadFinished(Loader<Cursor> loader, Cursor data) 

public void onLoaderReset(Loader<Cursor> loader)

其次，在使用getloadermanager().initLoader(id,data,callback)

来开始这个过程

下面是使用实例，异步获取联系人信息，加载到list上面

package com.example.u3.actionbartest2;

import android.app.Fragment;
import android.app.ListFragment;
import android.app.LoaderManager;
import android.content.CursorLoader;
import android.content.Loader;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.ContactsContract;
import android.text.AndroidCharacter;
import android.widget.SimpleCursorAdapter;


/**
 * Created by U3 on 2015/3/10.
 */
public class TestFragment extends ListFragment implements LoaderManager.LoaderCallbacks<Cursor>{
    private SimpleCursorAdapter madapter;
    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        madapter = new SimpleCursorAdapter(getActivity(), android.R.layout.activity_list_item,null,new String[]{ContactsContract.Contacts.DISPLAY_NAME,ContactsContract.Contacts.CONTACT_STATUS},new int[]{android.R.id.text1,android.R.id.text2},0);
        setListAdapter(madapter);
        getLoaderManager().initLoader(0,null,this);
    }
    static final String[] CONTACTS_SUMMARY_PROJECTION = new String[] {
            ContactsContract.Contacts._ID,
            ContactsContract.Contacts.DISPLAY_NAME,
            ContactsContract.Contacts.CONTACT_STATUS,
          //  ContactsContract.Contacts.CONTACT_PRESENCE,
           // ContactsContract.Contacts.PHOTO_ID,
          //  ContactsContract.Contacts.LOOKUP_KEY,
    };
    @Override
    public Loader<Cursor> onCreateLoader(int id, Bundle args) {
        Uri uri;
        uri = ContactsContract.Contacts.CONTENT_URI;
        String select = "(("+ContactsContract.Contacts.DISPLAY_NAME+" NOTNULL) AND ("+ ContactsContract.Contacts.HAS_PHONE_NUMBER +"=1) AND ("+ ContactsContract.Contacts.DISPLAY_NAME +" != ''))";
        /*String select = "((" + ContactsContract.Contacts.DISPLAY_NAME + " NOTNULL) AND ("
                + ContactsContract.Contacts.HAS_PHONE_NUMBER + "=1) AND ("
                + ContactsContract.Contacts.DISPLAY_NAME + " != '' ))";*/
        return new CursorLoader(getActivity(),uri,CONTACTS_SUMMARY_PROJECTION,select,null,null);
    }

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

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