shaobin0604
1/6/2014 - 9:35 AM
Loader
Loader
/**
* Demonstration of the use of a CursorLoader to load and display contacts
* data in a fragment.
*/
public class LoaderCursor extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
FragmentManager fm = getFragmentManager();
// Create the list fragment and add it as our sole content.
if (fm.findFragmentById(android.R.id.content) == null) {
CursorLoaderListFragment list = new CursorLoaderListFragment();
fm.beginTransaction().add(android.R.id.content, list).commit();
}
}
public static class CursorLoaderListFragment extends ListFragment
implements LoaderManager.LoaderCallbacks<Cursor> {
// This is the Adapter being used to display the list's data.
SimpleCursorAdapter mAdapter;
// If non-null, this is the current filter the user has provided.
String mCurFilter;
@Override public void onActivityCreated(Bundle savedInstanceState) {
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(0, null, this);
}
@Override public void onListItemClick(ListView l, View v, int position, long id) {
// Insert desired behavior here.
Log.i("FragmentComplexList", "Item clicked: " + id);
}
// These are the Contacts rows that we will retrieve.
static final String[] CONTACTS_SUMMARY_PROJECTION = new String[] {
Contacts._ID,
Contacts.DISPLAY_NAME,
Contacts.CONTACT_STATUS,
Contacts.CONTACT_PRESENCE,
Contacts.PHOTO_ID,
Contacts.LOOKUP_KEY,
};
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
// This is called when a new Loader needs to be created. This
// sample only has one Loader, so we don't care about the ID.
// First, pick the base URI to use depending on whether we are
// currently filtering.
Uri baseUri;
if (mCurFilter != null) {
baseUri = Uri.withAppendedPath(Contacts.CONTENT_FILTER_URI,
Uri.encode(mCurFilter));
} else {
baseUri = Contacts.CONTENT_URI;
}
// Now create and return a CursorLoader that will take care of
// creating a Cursor for the data being displayed.
String select = "((" + Contacts.DISPLAY_NAME + " NOTNULL) AND ("
+ Contacts.HAS_PHONE_NUMBER + "=1) AND ("
+ Contacts.DISPLAY_NAME + " != '' ))";
return new CursorLoader(getActivity(), baseUri,
CONTACTS_SUMMARY_PROJECTION, select, null,
Contacts.DISPLAY_NAME + " COLLATE LOCALIZED ASC");
}
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
// Swap the new cursor in. (The framework will take care of closing the
// old cursor once we return.)
mAdapter.swapCursor(data);
// The list should now be shown.
if (isResumed()) {
setListShown(true);
} else {
setListShownNoAnimation(true);
}
}
public void onLoaderReset(Loader<Cursor> loader) {
// This is called when the last Cursor provided to onLoadFinished()
// above is about to be closed. We need to make sure we are no
// longer using it.
mAdapter.swapCursor(null);
}
}
} public <D> Loader<D> initLoader(int id, Bundle args, LoaderManager.LoaderCallbacks<D> callback) {
if (mCreatingLoader) {
throw new IllegalStateException("Called while creating a loader");
}
LoaderInfo info = mLoaders.get(id);
if (info == null) {
// Loader doesn't already exist; create.
info = createAndInstallLoader(id, args, (LoaderManager.LoaderCallbacks<Object>)callback);
if (DEBUG) Log.v(TAG, " Created new loader " + info);
} else {
if (DEBUG) Log.v(TAG, " Re-using existing loader " + info);
info.mCallbacks = (LoaderManager.LoaderCallbacks<Object>)callback;
}
if (info.mHaveData && mStarted) {
// If the loader has already generated its data, report it now.
info.callOnLoadFinished(info.mLoader, info.mData);
}
return (Loader<D>)info.mLoader;
}
private LoaderInfo createAndInstallLoader(int id, Bundle args,
LoaderManager.LoaderCallbacks<Object> callback) {
try {
mCreatingLoader = true;
LoaderInfo info = createLoader(id, args, callback);
installLoader(info);
return info;
} finally {
mCreatingLoader = false;
}
}
private LoaderInfo createLoader(int id, Bundle args,
LoaderManager.LoaderCallbacks<Object> callback) {
LoaderInfo info = new LoaderInfo(id, args, (LoaderManager.LoaderCallbacks<Object>)callback);
Loader<Object> loader = callback.onCreateLoader(id, args);
info.mLoader = (Loader<Object>)loader;
return info;
}
void installLoader(LoaderInfo info) {
mLoaders.put(info.mId, info);
if (mStarted) {
// The activity will start all existing loaders in it's onStart(),
// so only start them here if we're past that point of the activitiy's
// life cycle
info.start();
}
}
void start() {
if (mLoader != null) {
if (!mListenerRegistered) {
mLoader.registerListener(mId, this);
mListenerRegistered = true;
}
mLoader.startLoading();
}
}
Loader：
public final void startLoading() {
mStarted = true;
mReset = false;
mAbandoned = false;
onStartLoading();
}
CursorLoader:
protected void onStartLoading() {
if (mCursor != null) {
deliverResult(mCursor);
}
if (takeContentChanged() || mCursor == null) {
forceLoad();
}
}
AsynTaskLoader:
protected void onForceLoad() {
super.onForceLoad();
cancelLoad();
mTask = new LoadTask();
if (DEBUG) Slog.v(TAG, "Preparing load: mTask=" + mTask);
executePendingTask();
}AsyncTaskLoader:
final class LoadTask extends AsyncTask<Void, Void, D> implements Runnable {
private final CountDownLatch mDone = new CountDownLatch(1);
// Set to true to indicate that the task has been posted to a handler for
// execution at a later time. Used to throttle updates.
boolean waiting;
/* Runs on a worker thread */
@Override
protected D doInBackground(Void... params) {
if (DEBUG) Slog.v(TAG, this + " >>> doInBackground");
try {
D data = AsyncTaskLoader.this.onLoadInBackground();
return data;
} catch (OperationCanceledException ex) {
}
}
/* Runs on the UI thread */
@Override
protected void onPostExecute(D data) {
if (DEBUG) Slog.v(TAG, this + " onPostExecute");
try {
AsyncTaskLoader.this.dispatchOnLoadComplete(this, data);
} finally {
mDone.countDown();
}
}
}
AsyncTaskLoader：
protected D onLoadInBackground() {
return loadInBackground();
}
CursorLoader:
public Cursor loadInBackground() {
try {
Cursor cursor = getContext().getContentResolver().query(mUri, mProjection, mSelection,
mSelectionArgs, mSortOrder, mCancellationSignal);
if (cursor != null) {
// Ensure the cursor window is filled
cursor.getCount();
registerContentObserver(cursor, mObserver);
}
return cursor;
} finally {
synchronized (this) {
mCancellationSignal = null;
}
}
}AsyncTaskLoader:
final class LoadTask extends AsyncTask<Void, Void, D> implements Runnable {
private final CountDownLatch mDone = new CountDownLatch(1);
// Set to true to indicate that the task has been posted to a handler for
// execution at a later time. Used to throttle updates.
boolean waiting;
/* Runs on a worker thread */
@Override
protected D doInBackground(Void... params) {
if (DEBUG) Slog.v(TAG, this + " >>> doInBackground");
try {
D data = AsyncTaskLoader.this.onLoadInBackground();
return data;
} catch (OperationCanceledException ex) {
}
}
/* Runs on the UI thread */
@Override
protected void onPostExecute(D data) {
if (DEBUG) Slog.v(TAG, this + " onPostExecute");
try {
AsyncTaskLoader.this.dispatchOnLoadComplete(this, data);
} finally {
mDone.countDown();
}
}
}
AsyncTaskLoader：
protected D onLoadInBackground() {
return loadInBackground();
}
CursorLoader:
public Cursor loadInBackground() {
try {
Cursor cursor = getContext().getContentResolver().query(mUri, mProjection, mSelection,
mSelectionArgs, mSortOrder, mCancellationSignal);
if (cursor != null) {
// Ensure the cursor window is filled
cursor.getCount();
registerContentObserver(cursor, mObserver);
}
return cursor;
} finally {
synchronized (this) {
mCancellationSignal = null;
}
}public void onChange(boolean selfChange) {
onContentChanged();
}
public void onContentChanged() {
if (mStarted) {
forceLoad(); //这里重新发送请求.
} else {
// This loader has been stopped, so we don't want to load
// new data right now... but keep track of it changing to
// refresh later if we start again.
mContentChanged = true;
}
}Activity:
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(null, mLoadersStarted, false);
}
mCheckedForLoaderManager = true;
}
getApplication().dispatchActivityStarted(this);
}
LoaderManagerImp：
void doStart() {
if (DEBUG) Log.v(TAG, "Starting in " + this);
if (mStarted) {
RuntimeException e = new RuntimeException("here");
e.fillInStackTrace();
Log.w(TAG, "Called doStart when already started: " + this, e);
return;
}
mStarted = true;
// Call out to sub classes so they can start their loaders
// Let the existing loaders know that we want to be notified when a load is complete
for (int i = mLoaders.size()-1; i >= 0; i--) {
mLoaders.valueAt(i).start();
}
}