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A version of LoaderTestCase that works with Support V4 Loaders
* Copyright (C) 2010 The Android Open Source Project
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License
import android.os.AsyncTask;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.test.AndroidTestCase;
import java.util.concurrent.ArrayBlockingQueue;
* A convenience class for testing {@link Loader}s. This test case
* provides a simple way to synchronously get the result from a Loader making
* it easy to assert that the Loader returns the expected result.
public class SupportLoaderTestCase extends AndroidTestCase {
static {
// Force class loading of AsyncTask on the main thread so that it's handlers are tied to
// the main thread and responses from the worker thread get delivered on the main thread.
// The tests are run on another thread, allowing them to block waiting on a response from
// the code running on the main thread. The main thread can't block since the AysncTask
// results come in via the event loop.
new AsyncTask<Void, Void, Void>() {
protected Void doInBackground(Void... args) {
return null;
protected void onPostExecute(Void result) {
* Runs a Loader synchronously and returns the result of the load. The loader will
* be started, stopped, and destroyed by this method so it cannot be reused.
* @param loader The loader to run synchronously
* @return The result from the loader
public <T> T getLoaderResultSynchronously(final Loader<T> loader) {
// The test thread blocks on this queue until the loader puts it's result in
final ArrayBlockingQueue<T> queue = new ArrayBlockingQueue<T>(1);
// This callback runs on the "main" thread and unblocks the test thread
// when it puts the result into the blocking queue
final Loader.OnLoadCompleteListener<T> listener = new Loader.OnLoadCompleteListener<T>() {
public void onLoadComplete(Loader<T> completedLoader, T data) {
// Shut the loader down
// Store the result, unblocking the test thread
// This handler runs on the "main" thread of the process since AsyncTask
// is documented as needing to run on the main thread and many Loaders use
// AsyncTask
final Handler mainThreadHandler = new Handler(Looper.getMainLooper()) {
public void handleMessage(Message msg) {
loader.registerListener(0, listener);
// Ask the main thread to start the loading process
// Block on the queue waiting for the result of the load to be inserted
T result;
while (true) {
try {
result = queue.take();
} catch (InterruptedException e) {
throw new RuntimeException("waiting thread interrupted", e);
return result;
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