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);
}
}