# AsyncTaskLoaderDemo **Repository Path**: happyxin/AsyncTaskLoaderDemo ## Basic Information - **Project Name**: AsyncTaskLoaderDemo - **Description**: AsyncTaskLoader用法解析以及demo - **Primary Language**: Unknown - **License**: Not specified - **Default Branch**: master - **Homepage**: None - **GVP Project**: No ## Statistics - **Stars**: 0 - **Forks**: 0 - **Created**: 2020-08-23 - **Last Updated**: 2020-12-19 ## Categories & Tags **Categories**: Uncategorized **Tags**: None ## README ### ### `AsyncTaskLoader` 是在Android 3.0加入了，需要兼容更低版本可以使用V4包，`AsyncTaskLoader`只能在`Fragment` 和 `Activity`上使用，并且生命周期跟随`Activity`的`onStart()`，`onStop()`和`onDestory()`，内部线程使用`AsyncTask`和 v4包中使用`ModernAsyncTask`,如果使用的`AsyncTask`默认`Executor` 不会是的`SERIAL_EXECUTOR`（一次只能执行一个任务）。 #### 1.AsyncTaskLoader的优缺点 > >优点：使用`AsyncTask`执行数据请求，如果当前在Activity关闭后还没有执行完成，那么Activity的就会被持有，因而导致内存泄漏,通常我们的做法是在`Activity`或者`Fragment`中的`onDestory()`方法中做一些数据清理工作，以及引用持有的清理工作，而`AsyncTaskLoader` 有生命周期的管理则会帮我们处理好这些。 > > >缺点：我们只能在`Activity`或者`Fragment`中使用，并且不能使用`AsyncTask`的progress > #### 2.Loader生命周期管理 > >`AsyncTaskLoader`最终通过`LoaderManager` 进行生命周期管理，数据分发以及回调，在`Activity`中有一个`LoaderManager` `mLoaderManager`实例，我们在`Activity`或者`Fragment` 中调用`getLoaderManager()`创建出这个实例。 >`mLoaderManager`在Activity中生命周期的管理分别是： > 1.`onStart()` protected void onStart() { if (DEBUG_LIFECYCLE) Slog.v(TAG, "onStart " + this); mCalled = true; if (!mLoadersStarted) { mLoadersStarted = true; if (mLoaderManager != null) { mLoaderManager.doStart(); } else if (!mCheckedForLoaderManager) { mLoaderManager = getLoaderManager("(root)", mLoadersStarted, false); } mCheckedForLoaderManager = true; } getApplication().dispatchActivityStarted(this); } 2.`performStop()` final void performStop() { mDoReportFullyDrawn = false; if (mLoadersStarted) { mLoadersStarted = false; if (mLoaderManager != null) { if (!mChangingConfigurations) { mLoaderManager.doStop(); } else { mLoaderManager.doRetain(); } } } 3.`performDestroy()` final void performDestroy() { mDestroyed = true; mWindow.destroy(); mFragments.dispatchDestroy(); onDestroy(); if (mLoaderManager != null) { mLoaderManager.doDestroy(); } if (mVoiceInteractor != null) { mVoiceInteractor.detachActivity(); } } #### 3.使用`AsyncTaskLoader` > >##### 1. 在Activity中实现`LoaderManager.LoaderCallbacks` > > `public class MainActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks> { ` > >##### 2. 实现三个方法： > > > @Override public Loader> onCreateLoader(int id, Bundle args) { //args 是getSupportLoaderManager().initLoader传过来的数据 Log.e("branch", "onCreateLoader"); return new AppListLoader(this); } @Override public void onLoadFinished(Loader> loader, List data) { Log.e("branch", "onLoadFinished-》 " + data); mListApps = data; mApplistAdapter.notifyDataSetChanged(); if (progressDialog != null) { progressDialog.dismiss(); } } @Override public void onLoaderReset(Loader> loader) { Log.e("branch", "onLoaderReset"); if (progressDialog != null) { progressDialog.dismiss(); } mListApps = null; mApplistAdapter.notifyDataSetChanged(); } > > 在`onCreateLoader` 方法中创建我们的Loader，在Activity的onCreate()或者其他地方调用方法中调用Loader init 方法，如 @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); startLoad(); } private void startLoad() { progressDialog = new ProgressDialog(this); progressDialog.show(); getSupportLoaderManager().initLoader(1, null, this); } > 当你想放弃上一次的数据是，可以使用`getLoaderManager().restartLoader(0, null, this);` public boolean onTextChanged(String newText) { // Called when the action bar search text has changed. Update // the search filter, and restart the loader to do a new query // with this filter. getLoaderManager().restartLoader(0, null, this); return true; } >这样写完我们的Loader就开始加载数据了 #### 4.AppListLoader的实现 > > 继承 `AsyncTaskLoader` ,实现以下几个方法 > public class AppListLoader extends AsyncTaskLoader> { List mApps; PackageManager mPm; 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 loadInBackground() { // Retrieve all known applications. List apps = mPm.getInstalledApplications( PackageManager.GET_UNINSTALLED_PACKAGES | PackageManager.GET_DISABLED_COMPONENTS | PackageManager.GET_META_DATA); if (apps == null) { apps = new ArrayList(); } // Done! return apps; } /** * 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 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 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); } if (takeContentChanged() || mApps == null) { // 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 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; } } /** * Helper function to take care of releasing resources associated with an actively loaded data * set. */ protected void onReleaseResources(List apps) { // For a simple List<> there is nothing to do. For something // like a Cursor, we would close it here. } } #### 5.效果图 ![效果图](https://raw.githubusercontent.com/goodbranch/AndroidNote/master/note/image/asynctaskloaderdemo.png) #### 6.demo > >[源码](https://github.com/goodbranch/AsyncTaskLoaderDemo.git) > >[Apk](https://raw.githubusercontent.com/goodbranch/AndroidNote/master/note/Apk/AsyncTaskLoaderDemo.apk)