Android多线程编程之四：Loaders

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Loader的异步数据加载方式，给出API上Demo的程序供大家参考怎么使用

package com.example.loadertest;

import android.app.Activity;
import android.app.FragmentManager;
import android.app.ListFragment;
import android.app.LoaderManager.LoaderCallbacks;
import android.content.CursorLoader;
import android.content.Loader;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.ContactsContract.Contacts;
import android.text.TextUtils;
import android.util.Log;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.ListView;
import android.widget.SearchView;
import android.widget.SearchView.OnQueryTextListener;
import android.widget.SimpleCursorAdapter;

public class LoaderTestActivity extends Activity {
    private static final String TAG = "LoaderTestActivity";

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // setContentView(R.layout.main);
        FragmentManager fm = getFragmentManager();
        if (fm.findFragmentById(android.R.id.content) == null) {
            CursorLoaderListFragment list = new CursorLoaderListFragment();
            fm.beginTransaction().add(android.R.id.content, list).commit();
        }
    }

    public class CursorLoaderListFragment extends ListFragment implements
            OnQueryTextListener, LoaderCallbacks<Cursor> {
        SimpleCursorAdapter adapter;// 显示数据列表
        String mCurFilter;// 过滤查询

        @Override
        public void onActivityCreated(Bundle savedInstanceState) {// 在此方法中进行fragment的布局操作
            super.onActivityCreated(savedInstanceState);
            setEmptyText("No phone number");
            setHasOptionsMenu(true);// 设置ActionBar是否有操作按钮
            adapter = new SimpleCursorAdapter(getActivity(),
                    android.R.layout.simple_list_item_2, null, new String[] {
                            Contacts.DISPLAY_NAME, Contacts.CONTACT_STATUS },
                    new int[] { android.R.id.text1, android.R.id.text2 }, 0);
            setListAdapter(adapter);
            setListShown(false);// 设置进度条显示
            // 初始化loader 创建新loader或者加载已存在的loader
            getLoaderManager().initLoader(0, null, this);
        }

        @Override
        public void onListItemClick(ListView l, View v, int position, long id) {
            super.onListItemClick(l, v, position, id);
            Log.i(TAG, "List Item clicked: " + id);
        }

        @Override
        public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
            super.onCreateOptionsMenu(menu, inflater);
            // 添加一个Menu按钮
            MenuItem item = menu.add("Search");
            item.setIcon(android.R.drawable.ic_menu_search);
            item.setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM
                    | MenuItem.SHOW_AS_ACTION_COLLAPSE_ACTION_VIEW);
            SearchView view = new SearchView(getActivity());
            view.setOnQueryTextListener(this);
            item.setActionView(view);// 添加SearchView
        }

        /*
         * 当Action Bar的Search按钮查询条件改变时回调此方法
         */
        @Override
        public boolean onQueryTextChange(String newString) {
            Log.i(TAG, "onQueryTextChange");
            String newFilter = TextUtils.isEmpty(newString) ? null : newString;
            // 当查询条件为空 or 当前查询条件和之前查询条件相同时都不做任何处理
            if ((mCurFilter == null && newFilter == null)
                    || (mCurFilter != null && mCurFilter.equals(newFilter)))
                return true;
            Log.i(TAG, "Result: " + newString);
            mCurFilter = newString;
            // 重新加载数据
            getLoaderManager().restartLoader(0, null, this);
            return true;
        }

        @Override
        public boolean onQueryTextSubmit(String arg0) {
            Log.i(TAG, "onQueryTextSubmit");
            // 不做任何处理
            return true;
        }

        // 查询后的返回字段
        final String[] CONTANCTS_PROJECTION = new String[] { Contacts._ID,
                Contacts.DISPLAY_NAME, Contacts.CONTACT_STATUS,
                Contacts.CONTACT_PRESENCE, Contacts.PHOTO_ID,
                Contacts.LOOKUP_KEY };

        /*
         * 当需要创建新的Loader时回调此方法
         */
        @Override
        public Loader<Cursor> onCreateLoader(int id, Bundle arg1) {
            Log.i(TAG, "onCreateLoader");
            // 本例子只涉及一个Loader，所以不用关心id
            Uri baseuUri;
            // 拼接URI
            if (mCurFilter == null || "".equals(mCurFilter)) {
                baseuUri = Contacts.CONTENT_URI;
            } else {
                baseuUri = Uri.withAppendedPath(Contacts.CONTENT_FILTER_URI,
                        Uri.encode(mCurFilter));
                Log.i(TAG, "mCurFilter: " + mCurFilter);
            }

            // 创建SQL查询语句
            String select = "((" + Contacts.DISPLAY_NAME + " NOTNULL) AND ("
                    + Contacts.HAS_PHONE_NUMBER + "=1) AND ("
                    + Contacts.DISPLAY_NAME + " != '' ))";
            // 返回Loader对象该对象将会传递给 onLoadFinished 回调方法
            return new CursorLoader(getActivity(), baseuUri,
                    CONTANCTS_PROJECTION, select, null, Contacts.DISPLAY_NAME
                            + " COLLATE LOCALIZED ASC");
        }

        @Override
        public void onLoadFinished(Loader<Cursor> arg0, Cursor cursor) {
            Log.i(TAG, "onLoadFinished");
            // 更新cursor（备注：不用关心cursor的回收，framework会负责回收之前的cursor对象）
            adapter.swapCursor(cursor);
            // 显示list数据
            if (isResumed()) {
                setListShown(true);
            } else {
                setListShownNoAnimation(true);
            }
        }

        @Override
        public void onLoaderReset(Loader<Cursor> arg0) {
            // 该方法会在之前cursor的 onLoadFinished之后调用
            // 为了让framework及时回收cursor对象，必须把引用置为null
            Log.i(TAG, "onLoaderReset");
            adapter.swapCursor(null);
        }
    }
}

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