Loaders

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

LoaderManager.LoaderCallbacks

onCreateLoader()

Loader

onLoadFinished()

onLoaderReset()

/**
* 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.
}
}