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Loaders，獲取數據的東西。

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總體流程是：通過getLoaderManager().initLoader(0,null,this)獲得Loader，如果沒有，那么就會調用接口函數獲取，注意：有ID，所以要在獲取的接口函數里進行相應的選擇。

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?會自動更新數據；

一個主要依賴Activity或者Fragment存在的。

通過getLoaderManager().initLoader(0,null,this)方法初始化LOADER。

要繼承LoaderManager.LoaderCallbacks，包括：

LoaderManager.LoaderCallbacks includes these methods:

• onCreateLoader() — Instantiate and return a new Loader for the given ID.

• onLoadFinished() — Called when a previously created loader has finished its load.

• onLoaderReset() — Called when a previously created loader is being reset, thus making its data unavailable.

These methods are described in more detail in the following sections.

　　第一個用于創建LOADER，一般來說，只有init的時候ID對應的LOADER不在的時候才會運行該方法。

　　第二個一般用來獲取數據后的填充適配器。

　　第三個用于重置。

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　　Loader可以自定義，一般使用繼承AsyncTaskLoader的類。

　　

/*** A custom Loader that loads all of the installed applications.*/ public static class AppListLoader extends AsyncTaskLoader<List<AppEntry>> {final InterestingConfigChanges mLastConfig = new InterestingConfigChanges();final PackageManager mPm;List<AppEntry> mApps;PackageIntentReceiver mPackageObserver;public AppListLoader(Context context) {super(context);// Retrieve the package manager for later use; note we don't// use 'context' directly but instead the save global application// context returned by getContext().mPm = getContext().getPackageManager();}/*** This is where the bulk of our work is done. This function is* called in a background thread and should generate a new set of* data to be published by the loader.*/@Override public List<AppEntry> loadInBackground() {// Retrieve all known applications.List<ApplicationInfo> apps = mPm.getInstalledApplications(PackageManager.GET_UNINSTALLED_PACKAGES |PackageManager.GET_DISABLED_COMPONENTS);if (apps == null) {apps = new ArrayList<ApplicationInfo>();}final Context context = getContext();// Create corresponding array of entries and load their labels.List<AppEntry> entries = new ArrayList<AppEntry>(apps.size());for (int i=0; i<apps.size(); i++) {AppEntry entry = new AppEntry(this, apps.get(i));entry.loadLabel(context);entries.add(entry);}// Sort the list. Collections.sort(entries, ALPHA_COMPARATOR);// Done!return entries;}/*** Called when there is new data to deliver to the client. The* super class will take care of delivering it; the implementation* here just adds a little more logic.*/@Override public void deliverResult(List<AppEntry> apps) {if (isReset()) {// An async query came in while the loader is stopped. We// don't need the result.if (apps != null) {onReleaseResources(apps);}}List<AppEntry> oldApps = mApps;mApps = apps;if (isStarted()) {// If the Loader is currently started, we can immediately// deliver its results.super.deliverResult(apps);}// At this point we can release the resources associated with// 'oldApps' if needed; now that the new result is delivered we// know that it is no longer in use.if (oldApps != null) {onReleaseResources(oldApps);}}/*** Handles a request to start the Loader.*/@Override protected void onStartLoading() {if (mApps != null) {// If we currently have a result available, deliver it// immediately. deliverResult(mApps);}// Start watching for changes in the app data.if (mPackageObserver == null) {mPackageObserver = new PackageIntentReceiver(this);}// Has something interesting in the configuration changed since we// last built the app list?boolean configChange = mLastConfig.applyNewConfig(getContext().getResources());if (takeContentChanged() || mApps == null || configChange) {// If the data has changed since the last time it was loaded// or is not currently available, start a load. forceLoad();}}/*** Handles a request to stop the Loader.*/@Override protected void onStopLoading() {// Attempt to cancel the current load task if possible. cancelLoad();}/*** Handles a request to cancel a load.*/@Override public void onCanceled(List<AppEntry> apps) {super.onCanceled(apps);// At this point we can release the resources associated with 'apps'// if needed. onReleaseResources(apps);}/*** Handles a request to completely reset the Loader.*/@Override protected void onReset() {super.onReset();// Ensure the loader is stopped onStopLoading();// At this point we can release the resources associated with 'apps'// if needed.if (mApps != null) {onReleaseResources(mApps);mApps = null;}// Stop monitoring for changes.if (mPackageObserver != null) {getContext().unregisterReceiver(mPackageObserver);mPackageObserver = null;}}/*** Helper function to take care of releasing resources associated* with an actively loaded data set.*/protected void onReleaseResources(List<AppEntry> apps) {// For a simple List<> there is nothing to do. For something// like a Cursor, we would close it here. } }

上面是官方的代碼。

構造方法傳入context。

loadInBackground是后臺真正獲取數據的代碼。

deliverResult提交數據給客戶端，可以直接返回。

onStartLoading處理要開始的請求，官方在這里進行了更新的監聽。

onStopLoading要求停止，官方直接使用cancelLoad()。

onCanceled()取消的操作，官方建議對資源進行釋放。

onReset，重置，詳細看代碼。

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這樣的話，就能從頭到尾自定義和使用一個Loader了。

轉載于:https://www.cnblogs.com/yutoulck/p/3619264.html

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