Android 3.0中提供了一个新概念Loaders,这两天看了之前Contacts的源码,其中自己写了通话记录部分,发现源码里面有很多LoaderManager的使用,现在做一个总结,记录一下LoaderManager的基本用法:
这个其实是分为两部分:LoaderManager和自定义Loader,比如像加载联系人,短信这些系统提供ContentProvider的数据时,其实就是返回一个标准cursor,那我们就没必要自定义loader 直接用loaderManager来管理这个CursorLoader,这是一种简单普遍的情况。还有一种就是我们要加载非cursor类型的数据时,就必须自定义loader了。
1.
LoaderManager和CursorLoader
举例用一个listFragment加载联系人,那么让它实现LoaderManager.LoaderCallbacks<Cursor> 接口,必须重写下面3个方法:
onCreateLoader: 这个是创建一个CursorLoader并返回,我们在里面new一个CursorLoader并返回就OK了
onLoadFinished: 这个是加载完成后更新UI,在这里就是setAdapter了 而这个加载过程其实就是在CursorLoader里面完成的,只不过系统帮我们完成了,而如果自定义loader的话就要自己完成,这就是区别!
onLoaderReset: loader的重置,在这里一般让UI不显示数据就行
就这么3个方法就可以完成数据加载了,核心就是把CursorLoader构造出来,至于加载过程,数据监听更新这些就有系统去完成吧!
<span style="font-size:14px;">public class ContactsFragment extends ListFragment implements LoaderManager.LoaderCallbacks <Cursor>{ private SimpleCursorAdapter mAdapter; private final String[] CONTACTS_PROJECTION = new String[]{Contacts._ID, Co<span style="font-size:14px;">ntacts.DISPL</span>AY_NAME, Contacts.CONTACT_STATUS, Contacts.CONTACT_PRESENCE, Contacts.PHOTO_ID, Contacts.LOOKUP_KEY, }; @Override public void onActivityCreated(Bundle savedInstanceState) { // TODO Auto-generated method stub super.onActivityCreated(savedInstanceState); setEmptyText("当前没有联系人"); mAdapter = 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(mAdapter); getLoaderManager().initLoader(1, null, this); } @Override public Loader<Cursor> onCreateLoader(int arg0, Bundle arg1) { // TODO Auto-generated method stub String select = "((" + Contacts.DISPLAY_NAME + " NOTNULL) AND (" + Contacts.HAS_PHONE_NUMBER + "=1) AND (" + Contacts.DISPLAY_NAME + " != '' ))"; return new CursorLoader(getActivity(), Contacts.CONTENT_URI, <span style="font-size:14px;"> </span>CONTACTS_PROJECTION, select, null, Contacts.DISPLAY_NAME + " COLLATE LOCALIZED ASC"); } @Override public void onLoadFinished(Loader<Cursor> arg0, Cursor arg1) { // TODO Auto-generated method stub mAdapter.swapCursor(arg1); } @Override public void onLoaderReset(Loader<Cursor> arg0) { // TODO Auto-generated method stub mAdapter.swapCursor(null); } }</span>
2. 自定义Loader
但有些拿不到cursor这样的数据,我们就需要自定义Loader,其实在Loader里面只需要重写两个方法:一个onStartLoading,还有一个loadInBackground,但为了代码更加完善一些,再重写另外几个方法: onStopLoading onReset onCanceled,可以类比activity的生命周期,然后参考google文档进行重写,先贴出代码:
public class MySmsLoader extends AsyncTaskLoader<List<SmsEntry>> { private PackageManager mPm; private InstalledAppsObserver mAppsObserver; public MySmsLoader(Context context) { super(context); // TODO Auto-generated constructor stub mPm = getContext().getPackageManager(); Log.d("dml", "new一个MySmsLoader"); } @Override public List<SmsEntry> loadInBackground() { Log.d("dml", "loadInBackground--------" ); // TODO Auto-generated method stub // Retrieve all installed applications. List<ApplicationInfo> apps = mPm.getInstalledApplications(0); Log.d("dml", "apps >>>>>>>>>>" + apps); if (apps == null) { Log.d("dml", "apps null"); apps = new ArrayList<ApplicationInfo>(); } // Create corresponding array of entries and load their labels. List<SmsEntry> entries = new ArrayList<SmsEntry>(apps.size()); for (int i = 0; i < apps.size(); i++) { SmsEntry entry = new SmsEntry(); entry.setFrom_name(i+"::::::::"); entry.setSend_time(apps.get(i).packageName); entries.add(entry); } Log.d("dml", "entries---->>>>>>>>>----" + entries); return entries; } @Override protected void onStartLoading() { // TODO Auto-generated method stub super.onStartLoading(); if (mAppsObserver == null) { mAppsObserver = new InstalledAppsObserver(this); } forceLoad(); } @Override protected void onStopLoading() { // The Loader has been put in a stopped state, so we should attempt to // cancel the current load (if there is one). cancelLoad(); // Note that we leave the observer as is; Loaders in a stopped state // should still monitor the data source for changes so that the Loader // will know to force a new load if it is ever started again. } @Override protected void onReset() { // Ensure the loader is stopped. onStopLoading(); // The Loader is being reset, so we should stop monitoring for changes. if (mAppsObserver != null) { getContext().unregisterReceiver(mAppsObserver); mAppsObserver = null; } } @Override public void onCanceled(List<SmsEntry> apps) { // Attempt to cancel the current asynchronous load. super.onCanceled(apps); // The load has been canceled, so we should release the resources // associated with 'mApps'. releaseResources(apps); } private void releaseResources(List<SmsEntry> apps) { // For a simple List, there is nothing to do. For something like a Cursor, // we would close it in this method. All resources associated with the // Loader should be released here. } }
onStartLoading:注册一些监听器到loader上,并且执行一次forceLoad(); 否则loader不会开始工作
loadInBackground:不用说,在这里就是加载数据并且返回,其实这个数据就返回到了LoaderManager的
onLoadFinished方法第二个参数
onStopLoading:停止加载数据,但不要停止监听也不要释放数据,就可以随时重启loader
onReset:先确保已经停止加载数据了,然后释放掉监听器并设为null
onCanceled: 在这里可以释放资源,如果是list就不需要做什么了,但是象cursor或者打开了什么文件就应该关闭一下
这几个生命周期方法还不是非常清楚,但就象activity的生命周期一样,可以里面的细节不是很了解 但我们还是可以很熟练的使用activity,除了这几个还有一个deliverResult(),确实没弄懂,留到以后在体会吧!
下面就是监听器的代码,注意是在构造方法中绑定到loader:
public class InstalledAppsObserver extends BroadcastReceiver { private static final String TAG = "ADP_InstalledAppsObserver"; private static final boolean DEBUG = true; private MySmsLoader mLoader; public InstalledAppsObserver(MySmsLoader loader) { mLoader = loader; // Register for events related to application installs/removals/updates. IntentFilter filter = new IntentFilter(Intent.ACTION_PACKAGE_ADDED); filter.addAction(Intent.ACTION_PACKAGE_REMOVED); filter.addAction(Intent.ACTION_PACKAGE_CHANGED); filter.addDataScheme("package"); mLoader.getContext().registerReceiver(this, filter); // Register for events related to sdcard installation. IntentFilter sdFilter = new IntentFilter(); sdFilter.addAction(Intent.ACTION_EXTERNAL_APPLICATIONS_AVAILABLE); sdFilter.addAction(Intent.ACTION_EXTERNAL_APPLICATIONS_UNAVAILABLE); mLoader.getContext().registerReceiver(this, sdFilter); } @Override public void onReceive(Context context, Intent intent) { if (DEBUG) Log.i(TAG, "+++ The observer has detected an application change!" + " Notifying Loader... +++"); // Tell the loader about the change. mLoader.onContentChanged(); } }
剩下的工作就和之前一样了,在LoaderManager里面拿到loader返回的数据,更新UI:
public class SmsFragment extends ListFragment implements LoaderCallbacks <List<SmsEntry>>{ private SmsAdapter adapter; @Override public void onActivityCreated(Bundle savedInstanceState) { // TODO Auto-generated method stub super.onActivityCreated(savedInstanceState); Log.d("dml", "进入SmsFragment "); adapter = new SmsAdapter(getActivity()); setEmptyText("No applications"); setListAdapter(adapter); setListShown(false); getLoaderManager().initLoader(2, null, this); } @Override public Loader<List<SmsEntry>> onCreateLoader(int arg0, Bundle arg1) { // TODO Auto-generated method stub Log.d("dml", " onCreateLoader"); return new MySmsLoader(getActivity()); } @Override public void onLoadFinished(Loader<List<SmsEntry>> arg0, List<SmsEntry> arg1) { // TODO Auto-generated method stub Log.d("dml", " onLoadFinished>>>>>>>arg1: " + arg1); adapter.setData(arg1); if (isResumed()) { setListShown(true); } else { setListShownNoAnimation(true); } } @Override public void onLoaderReset(Loader<List<SmsEntry>> arg0) { // TODO Auto-generated method stub Log.d("dml", " onLoaderReset"); adapter.setData(null); } class SmsAdapter extends ArrayAdapter<SmsEntry>{ private LayoutInflater inflater; public SmsAdapter(Context context) { super(context,android.R.layout.simple_list_item_2); // TODO Auto-generated constructor stub Log.d("dml", " new SmsAdapter--------"); inflater = (LayoutInflater) context.getSystemService (context.LAYOUT_INFLATER_SERVICE); } @Override public View getView(int position, View convertView, ViewGroup parent) { // TODO Auto-generated method stub Log.d("dml", "getView-------- "); View view = convertView; ViewHolder holder; if(view==null){ view = inflater.inflate(R.layout.item, parent,false); holder = new ViewHolder(); holder.name = (TextView) view.findViewById(R.id.name); holder.date = (TextView)view.findViewById(R.id.date); view.setTag(holder); } else{ holder = (ViewHolder)view.getTag(); } SmsEntry item = getItem(position); Log.d("dml", "item-------- " + item); holder.name.setText(item.from_name); holder.date.setText(item.send_time); return view; } private class ViewHolder{ TextView name; TextView date; } public void setData(List<SmsEntry> data){ clear(); if(data!=null){ Log.d("dml", "data-------- " + data); for(int i=0;i<data.size();i++){ add(data.get(i)); } } } } }
可以看出这里的数据结构由原来的cursor变成了自定义的SmsEntry,另外在这里要学会自定义ArrayAdapter的用法,显示数据