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/* -*- Mode: Java; c-basic-offset: 4; tab-width: 4; indent-tabs-mode: nil; -*-
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
package org.mozilla.gecko.util;
import android.os.Handler;
import android.os.Looper;
/**
* Executes a background task and publishes the result on the UI thread.
*
* The standard {@link android.os.AsyncTask} only runs onPostExecute on the
* thread it is constructed on, so this is a convenience class for creating
* tasks off the UI thread.
*
* We use generics differently to Android's AsyncTask.
* Android uses a "Params" type parameter to represent the type of all the parameters to this task.
* It then uses arguments of type Params... to permit arbitrarily-many of these to be passed
* fluently.
*
* Unfortunately, since Java does not support generic array types (and since varargs desugars to a
* single array parameter) that behaviour exposes a hole in the type system. See:
* http://docs.oracle.com/javase/tutorial/java/generics/nonReifiableVarargsType.html#vulnerabilities
*
* Instead, we equivalently have a single type parameter "Param". A UiAsyncTask may take exactly one
* parameter of type Param. Since Param can be an array type, this no more restrictive than the
* other approach, it just provides additional type safety.
*/
public abstract class UIAsyncTask<Param, Result> {
/**
* Provide a convenient API for parameter-free UiAsyncTasks by wrapping parameter-taking methods
* from UiAsyncTask in parameterless equivalents.
*/
public static abstract class WithoutParams<InnerResult> extends UIAsyncTask<Void, InnerResult> {
public WithoutParams(Handler backgroundThreadHandler) {
super(backgroundThreadHandler);
}
public void execute() {
execute(null);
}
@Override
protected InnerResult doInBackground(Void unused) {
return doInBackground();
}
protected abstract InnerResult doInBackground();
}
final Handler mBackgroundThreadHandler;
private volatile boolean mCancelled;
private static Handler sHandler;
/**
* Creates a new asynchronous task.
*
* @param backgroundThreadHandler the handler to execute the background task on
*/
public UIAsyncTask(Handler backgroundThreadHandler) {
mBackgroundThreadHandler = backgroundThreadHandler;
}
private static synchronized Handler getUiHandler() {
if (sHandler == null) {
sHandler = new Handler(Looper.getMainLooper());
}
return sHandler;
}
private final class BackgroundTaskRunnable implements Runnable {
private final Param mParam;
public BackgroundTaskRunnable(Param param) {
mParam = param;
}
@Override
public void run() {
final Result result = doInBackground(mParam);
getUiHandler().post(new Runnable() {
@Override
public void run() {
if (mCancelled) {
onCancelled();
} else {
onPostExecute(result);
}
}
});
}
}
protected void execute(final Param param) {
getUiHandler().post(new Runnable() {
@Override
public void run() {
onPreExecute();
mBackgroundThreadHandler.post(new BackgroundTaskRunnable(param));
}
});
}
public final boolean cancel() {
mCancelled = true;
return mCancelled;
}
public final boolean isCancelled() {
return mCancelled;
}
protected void onPreExecute() { }
protected void onPostExecute(Result result) { }
protected void onCancelled() { }
protected abstract Result doInBackground(Param param);
}
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