Google is deprecating Android AsyncTask API in Android 11 and suggesting to use java.util.concurrent instead. you can check out the commit here
*
* #deprecated Use the standard <code>java.util.concurrent</code> or
* <a href="https://developer.android.com/topic/libraries/architecture/coroutines">
* Kotlin concurrency utilities</a> instead.
*/
#Deprecated
public abstract class AsyncTask<Params, Progress, Result> {
If you’re maintaining an older codebase with asynchronous tasks in Android, you’re likely going to have to change it in future. My question is that what should be proper replacement of the code snippet shown below using java.util.concurrent. It is a static inner class of an Activity. I am looking for something that will work with minSdkVersion 16
private static class LongRunningTask extends AsyncTask<String, Void, MyPojo> {
private static final String TAG = MyActivity.LongRunningTask.class.getSimpleName();
private WeakReference<MyActivity> activityReference;
LongRunningTask(MyActivity context) {
activityReference = new WeakReference<>(context);
}
#Override
protected MyPojo doInBackground(String... params) {
// Some long running task
}
#Override
protected void onPostExecute(MyPojo data) {
MyActivity activity = activityReference.get();
activity.progressBar.setVisibility(View.GONE);
populateData(activity, data) ;
}
}
You can directly use Executors from java.util.concurrent package.
I also searched about it and I found a solution in this Android Async API is Deprecated post.
Unfortunately, the post is using Kotlin, but after a little effort I have converted it into Java. So here is the solution.
ExecutorService executor = Executors.newSingleThreadExecutor();
Handler handler = new Handler(Looper.getMainLooper());
executor.execute(new Runnable() {
#Override
public void run() {
//Background work here
handler.post(new Runnable() {
#Override
public void run() {
//UI Thread work here
}
});
}
});
Pretty simple right? You can simplify it little more if you are using Java 8 in your project.
ExecutorService executor = Executors.newSingleThreadExecutor();
Handler handler = new Handler(Looper.getMainLooper());
executor.execute(() -> {
//Background work here
handler.post(() -> {
//UI Thread work here
});
});
Still, it cannot defeat kotlin terms of conciseness of the code, but better than the previous java version.
Hope this will help you. Thank You
private WeakReference<MyActivity> activityReference;
Good riddance that it's deprecated, because the WeakReference<Context> was always a hack, and not a proper solution.
Now people will have the opportunity to sanitize their code.
AsyncTask<String, Void, MyPojo>
Based on this code, Progress is actually not needed, and there is a String input + MyPojo output.
This is actually quite easy to accomplish without any use of AsyncTask.
public class TaskRunner {
private final Executor executor = Executors.newSingleThreadExecutor(); // change according to your requirements
private final Handler handler = new Handler(Looper.getMainLooper());
public interface Callback<R> {
void onComplete(R result);
}
public <R> void executeAsync(Callable<R> callable, Callback<R> callback) {
executor.execute(() -> {
final R result = callable.call();
handler.post(() -> {
callback.onComplete(result);
});
});
}
}
How to pass in the String? Like so:
class LongRunningTask implements Callable<MyPojo> {
private final String input;
public LongRunningTask(String input) {
this.input = input;
}
#Override
public MyPojo call() {
// Some long running task
return myPojo;
}
}
And
// in ViewModel
taskRunner.executeAsync(new LongRunningTask(input), (data) -> {
// MyActivity activity = activityReference.get();
// activity.progressBar.setVisibility(View.GONE);
// populateData(activity, data) ;
loadingLiveData.setValue(false);
dataLiveData.setValue(data);
});
// in Activity
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main_activity);
viewModel = ViewModelProviders.of(this).get(MyViewModel.class);
viewModel.loadingLiveData.observe(this, (loading) -> {
if(loading) {
progressBar.setVisibility(View.VISIBLE);
} else {
progressBar.setVisibility(View.GONE);
}
});
viewModel.dataLiveData.observe(this, (data) -> {
populateData(data);
});
}
This example used a single-threaded pool which is good for DB writes (or serialized network requests), but if you want something for DB reads or multiple requests, you can consider the following Executor configuration:
private static final Executor THREAD_POOL_EXECUTOR =
new ThreadPoolExecutor(5, 128, 1,
TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());
One of the simplest alternative is to use Thread
new Thread(new Runnable() {
#Override
public void run() {
// do your stuff
runOnUiThread(new Runnable() {
public void run() {
// do onPostExecute stuff
}
});
}
}).start();
If your project supports JAVA 8, you can use lambda:
new Thread(() -> {
// do background stuff here
runOnUiThread(()->{
// OnPostExecute stuff here
});
}).start();
According to the Android documentation AsyncTask was deprecated in API level 30 and it is suggested to use the standard java.util.concurrent or Kotlin concurrency utilities instead.
Using the latter it can be achieved pretty simple:
Create generic extension function on CoroutineScope:
fun <R> CoroutineScope.executeAsyncTask(
onPreExecute: () -> Unit,
doInBackground: () -> R,
onPostExecute: (R) -> Unit
) = launch {
onPreExecute() // runs in Main Thread
val result = withContext(Dispatchers.IO) {
doInBackground() // runs in background thread without blocking the Main Thread
}
onPostExecute(result) // runs in Main Thread
}
Use the function with any CoroutineScope which has Dispatchers.Main context:
In ViewModel:
class MyViewModel : ViewModel() {
fun someFun() {
viewModelScope.executeAsyncTask(onPreExecute = {
// ... runs in Main Thread
}, doInBackground = {
// ... runs in Worker(Background) Thread
"Result" // send data to "onPostExecute"
}, onPostExecute = {
// runs in Main Thread
// ... here "it" is the data returned from "doInBackground"
})
}
}
In Activity or Fragment:
lifecycleScope.executeAsyncTask(onPreExecute = {
// ... runs in Main Thread
}, doInBackground = {
// ... runs in Worker(Background) Thread
"Result" // send data to "onPostExecute"
}, onPostExecute = {
// runs in Main Thread
// ... here "it" is the data returned from "doInBackground"
})
To use viewModelScope or lifecycleScope add next line(s) to dependencies of the app's build.gradle file:
implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$LIFECYCLE_VERSION" // for viewModelScope
implementation "androidx.lifecycle:lifecycle-runtime-ktx:$LIFECYCLE_VERSION" // for lifecycleScope
At the time of writing final LIFECYCLE_VERSION = "2.3.0-alpha05"
UPDATE:
Also we can implement progress updating using onProgressUpdate function:
fun <P, R> CoroutineScope.executeAsyncTask(
onPreExecute: () -> Unit,
doInBackground: suspend (suspend (P) -> Unit) -> R,
onPostExecute: (R) -> Unit,
onProgressUpdate: (P) -> Unit
) = launch {
onPreExecute()
val result = withContext(Dispatchers.IO) {
doInBackground {
withContext(Dispatchers.Main) { onProgressUpdate(it) }
}
}
onPostExecute(result)
}
Using any CoroutineScope (viewModelScope/lifecycleScope, see implementations above) with Dispatchers.Main context we can call it:
someScope.executeAsyncTask(
onPreExecute = {
// ... runs in Main Thread
}, doInBackground = { publishProgress: suspend (progress: Int) -> Unit ->
// ... runs in Background Thread
// simulate progress update
publishProgress(50) // call `publishProgress` to update progress, `onProgressUpdate` will be called
delay(1000)
publishProgress(100)
"Result" // send data to "onPostExecute"
}, onPostExecute = {
// runs in Main Thread
// ... here "it" is a data returned from "doInBackground"
}, onProgressUpdate = {
// runs in Main Thread
// ... here "it" contains progress
}
)
Use this class to execute background task in Background Thread this class is work for all android API version include Android 11 also this code is same work like AsyncTask with doInBackground and onPostExecute methods
public abstract class BackgroundTask {
private Activity activity;
public BackgroundTask(Activity activity) {
this.activity = activity;
}
private void startBackground() {
new Thread(new Runnable() {
public void run() {
doInBackground();
activity.runOnUiThread(new Runnable() {
public void run() {
onPostExecute();
}
});
}
}).start();
}
public void execute(){
startBackground();
}
public abstract void doInBackground();
public abstract void onPostExecute();
}
After copying the above class, you can then use it with this:
new BackgroundTask(MainActivity.this) {
#Override
public void doInBackground() {
//put you background code
//same like doingBackground
//Background Thread
}
#Override
public void onPostExecute() {
//hear is result part same
//same like post execute
//UI Thread(update your UI widget)
}
}.execute();
Android deprecated AsyncTask API in Android 11 to get rid of a share of problems to begin with.
So, what's now?
Threads
Executers
RxJava
Listenable Futures
Coroutines 🔥
Why Coroutines?
Coroutines are the Kotlin way to do asynchronous programming. Compiler
support is stable since Kotlin 1.3, together with a
kotlinx.coroutines library -
Structured Concurrency
Non-blocking, sequential code
Cancellation propagation
Natural Exception Handling
Here I created a Alternative for AsyncTask using Coroutines which can be used same as AsyncTask without changing much code base in your project.
Create a new Abstract class AsyncTaskCoroutine which takes input parameter and output parameter datatypes of-course these parameters are optional :)
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.GlobalScope
import kotlinx.coroutines.async
import kotlinx.coroutines.launch
abstract class AsyncTaskCoroutine<I, O> {
var result: O? = null
//private var result: O
open fun onPreExecute() {}
open fun onPostExecute(result: O?) {}
abstract fun doInBackground(vararg params: I): O
fun <T> execute(vararg input: I) {
GlobalScope.launch(Dispatchers.Main) {
onPreExecute()
callAsync(*input)
}
}
private suspend fun callAsync(vararg input: I) {
GlobalScope.async(Dispatchers.IO) {
result = doInBackground(*input)
}.await()
GlobalScope.launch(Dispatchers.Main) {
onPostExecute(result)
}
}
}
2 . Inside Activity use this as same as your old AsycnTask now
new AsyncTaskCoroutine() {
#Override
public Object doInBackground(Object[] params) {
return null;
}
#Override
public void onPostExecute(#Nullable Object result) {
}
#Override
public void onPreExecute() {
}
}.execute();
InCase if you need to send pass params
new AsyncTaskCoroutine<Integer, Boolean>() {
#Override
public Boolean doInBackground(Integer... params) {
return null;
}
#Override
public void onPostExecute(#Nullable Boolean result) {
}
#Override
public void onPreExecute() {
}
}.execute();
Google recommends using Java’s Concurrency framework or Kotlin Coroutines. but Rxjava end to have much more flexibility and features then java concurrency so gained quite a bit of popularity.
I actually wrote two Medium stories about it:
AsyncTas is deprecated now what
AsyncTas is deprecated now what part 2
The first one is with Java and a workaround with Runnable, the second is a Kotlin and coroutines solution.
Both are with code examples of course.
The accepted answer is good. But...
I didn't see cancel() method implementation
So my implementation with possibility to cancel the running task (simulating cancellation) is below.
Cancel is needed to not run postExecute() method in case of task interruption.
public abstract class AsyncTaskExecutor<Params> {
public static final String TAG = "AsyncTaskRunner";
private static final Executor THREAD_POOL_EXECUTOR =
new ThreadPoolExecutor(5, 128, 1,
TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());
private final Handler mHandler = new Handler(Looper.getMainLooper());
private boolean mIsInterrupted = false;
protected void onPreExecute(){}
protected abstract Void doInBackground(Params... params);
protected void onPostExecute(){}
protected void onCancelled() {}
#SafeVarargs
public final void executeAsync(Params... params) {
THREAD_POOL_EXECUTOR.execute(() -> {
try {
checkInterrupted();
mHandler.post(this::onPreExecute);
checkInterrupted();
doInBackground(params);
checkInterrupted();
mHandler.post(this::onPostExecute);
} catch (InterruptedException ex) {
mHandler.post(this::onCancelled);
} catch (Exception ex) {
Log.e(TAG, "executeAsync: " + ex.getMessage() + "\n" + Debug.getStackTrace(ex));
}
});
}
private void checkInterrupted() throws InterruptedException {
if (isInterrupted()){
throw new InterruptedException();
}
}
public void cancel(boolean mayInterruptIfRunning){
setInterrupted(mayInterruptIfRunning);
}
public boolean isInterrupted() {
return mIsInterrupted;
}
public void setInterrupted(boolean interrupted) {
mIsInterrupted = interrupted;
}
}
Example of using this class:
public class MySearchTask extends AsyncTaskExecutor<String> {
public MySearchTask(){
}
#Override
protected Void doInBackground(String... params) {
// Your long running task
return null;
}
#Override
protected void onPostExecute() {
// update UI on task completed
}
#Override
protected void onCancelled() {
// update UI on task cancelled
}
}
MySearchTask searchTask = new MySearchTask();
searchTask.executeAsync("Test");
Here I also created an Alternative for AsyncTask using abstract class and it can be just copied as a class.
/app/src/main/java/../AsyncTasks.java
public abstract class AsyncTasks {
private final ExecutorService executors;
public AsyncTasks() {
this.executors = Executors.newSingleThreadExecutor();
}
private void startBackground() {
onPreExecute();
executors.execute(new Runnable() {
#Override
public void run() {
doInBackground();
new Handler(Looper.getMainLooper()).post(new Runnable() {
#Override
public void run() {
onPostExecute();
}
});
}
});
}
public void execute() {
startBackground();
}
public void shutdown() {
executors.shutdown();
}
public boolean isShutdown() {
return executors.isShutdown();
}
public abstract void onPreExecute();
public abstract void doInBackground();
public abstract void onPostExecute();
}
Implementation/ use of the above class
new AsyncTasks() {
#Override
public void onPreExecute() {
// before execution
}
#Override
public void doInBackground() {
// background task here
}
#Override
public void onPostExecute() {
// Ui task here
}
}.execute();
My custom replacement: https://github.com/JohnyDaDeveloper/AndroidAsync
It only works when the app is running (more specifically the activity which scheduled the task), but it's capable of updating the UI after the background task was completed
EDIT: My AsyncTask no longer reqires Activiy to function.
Just replace the whole class with this Thread and put it in a method to pass variables
new Thread(() -> {
// do background stuff here
runOnUiThread(()->{
// OnPostExecute stuff here
});
}).start();
and in Fragment add the Context to the runOnUiThread() methode:
new Thread(() -> {
// do background stuff here
context.runOnUiThread(()->{
// OnPostExecute stuff here
});
}).start();
You can use this custom class as an alternative of the AsyncTask<>, this is the same as AsyncTask so you not need to apply extra efforts for the same.
import android.os.Handler;
import android.os.Looper;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
public class TaskRunner {
private static final int CORE_THREADS = 3;
private static final long KEEP_ALIVE_SECONDS = 60L;
private static TaskRunner taskRunner = null;
private Handler handler = new Handler(Looper.getMainLooper());
private ThreadPoolExecutor executor;
private TaskRunner() {
executor = newThreadPoolExecutor();
}
public static TaskRunner getInstance() {
if (taskRunner == null) {
taskRunner = new TaskRunner();
}
return taskRunner;
}
public void shutdownService() {
if (executor != null) {
executor.shutdown();
}
}
public void execute(Runnable command) {
executor.execute(command);
}
public ExecutorService getExecutor() {
return executor;
}
public <R> void executeCallable(#NonNull Callable<R> callable, #NonNull OnCompletedCallback<R> callback) {
executor.execute(() -> {
R result = null;
try {
result = callable.call();
} catch (Exception e) {
e.printStackTrace(); // log this exception
} finally {
final R finalResult = result;
handler.post(() -> callback.onComplete(finalResult));
}
});
}
private ThreadPoolExecutor newThreadPoolExecutor() {
return new ThreadPoolExecutor(
CORE_THREADS,
Integer.MAX_VALUE,
KEEP_ALIVE_SECONDS,
TimeUnit.SECONDS,
new SynchronousQueue<>()
);
}
public interface OnCompletedCallback<R> {
void onComplete(#Nullable R result);
}
}
How to use it? Please follow the below examples.
With lambda expressions
TaskRunner.getInstance().executeCallable(() -> 1, result -> {
});
TaskRunner.getInstance().execute(() -> {
});
Without lambda expressions
TaskRunner.getInstance().executeCallable(new Callable<Integer>() {
#Override
public Integer call() throws Exception {
return 1;
}
}, new TaskRunner.OnCompletedCallback<Integer>() {
#Override
public void onComplete(#Nullable Integer result) {
}
});
TaskRunner.getInstance().execute(new Runnable() {
#Override
public void run() {
}
});
Note: Don't forget to shutdown executors service
TaskRunner.getInstance().shutdownService();
You can migrate to next approaches depends your needs
Thread + Handler
Executor
Future
IntentService
JobScheduler
RxJava
Coroutines (Kotlin)
[Android async variants]
My answer is similar to the others, but it is easier to read imo.
This is the class:
public class Async {
private static final ExecutorService executorService = Executors.newCachedThreadPool();
private static final Handler handler = new Handler(Looper.getMainLooper());
public static <T> void execute(Task<T> task) {
executorService.execute(() -> {
T t = task.doAsync();
handler.post(() -> {
task.doSync(t);
});
});
}
public interface Task<T> {
T doAsync();
void doSync(T t);
}
}
And here's an example on how to use it:
String url;
TextView responseCodeText;
Async.execute(new Async.Task<Integer>() {
#Override
public Integer doAsync() {
try {
HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();
return connection.getResponseCode();
} catch (IOException e) {
return null;
}
}
#Override
public void doSync(Integer responseCode) {
responseCodeText.setText("responseCode=" + responseCode);
}
});
This is my code
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
public abstract class AsyncTaskRunner<T> {
private ExecutorService executorService = null;
private Set<Callable<T>> tasks = new HashSet<>();
public AsyncTaskRunner() {
this.executorService = Executors.newSingleThreadExecutor();
}
public AsyncTaskRunner(int threadNum) {
this.executorService = Executors.newFixedThreadPool(threadNum);
}
public void addTask(Callable<T> task) {
tasks.add(task);
}
public void execute() {
try {
List<Future<T>> features = executorService.invokeAll(tasks);
List<T> results = new ArrayList<>();
for (Future<T> feature : features) {
results.add(feature.get());
}
this.onPostExecute(results);
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
this.onCancelled();
} finally {
executorService.shutdown();
}
}
protected abstract void onPostExecute(List<T> results);
protected void onCancelled() {
// stub
}
}
And usage example.
Extends the AsyncTaskRunner class,
class AsyncCalc extends AsyncTaskRunner<Integer> {
public void addRequest(final Integer int1, final Integer int2) {
this.addTask(new Callable<Integer>() {
#Override
public Integer call() throws Exception {
// Do something in background
return int1 + int2;
}
});
}
#Override
protected void onPostExecute(List<Integer> results) {
for (Integer answer: results) {
Log.d("AsyncCalc", answer.toString());
}
}
}
then use it!
AsyncCalc calc = new AsyncCalc();
calc.addRequest(1, 2);
calc.addRequest(2, 3);
calc.addRequest(3, 4);
calc.execute();
AsyncTask class does not seem to be removed any time soon, but we did simply un-deprecate it anyway, because:
We didn't want to add lots of suppress annotations.
The alternative solutions have too much boiler-plate, or in most cases, without any real advantage vs AsyncTask.
We did not want to re-invent the wheel.
We didn't want to fear the day it will finally be removed.
Refactoring takes too much time.
Example
Simply add below file to your project, then search for "android.os.AsyncTask" imports, and replase all to the packge you did choose for said file.
As you may already know, this is no big deal, and is basically what the well known AndroidX library does all the time.
Get AsyncTask.java file at: https://gist.github.com/top-master/0efddec3e2c35d77e30331e8c3bc725c
Docs says:
AsyncTask This class was deprecated in API level 30. Use the standard
java.util.concurrent or Kotlin concurrency utilities instead.
You need to use Handler or coroutines instead AsyncTask.
Use Handler for Java
new Handler(Looper.getMainLooper()).postDelayed(new Runnable() {
#Override
public void run() {
// Your Code
}
}, 3000);
Use Handler for Kotlin
Handler(Looper.getMainLooper()).postDelayed({
// Your Code
}, 3000)
I have the following AsyncTask class which I want to handle multiple api calls and return a List back to my activity. I am having a problems trying to make this work.
How can I return an object back to my activity when onPostExecute() method does not return anything?
public class NetworkCall extends AsyncTask<Call, Void, List<Student>> {
#Override
protected List<Students> doInBackground(Call... calls) {
try {
Call<Students> call = calls[0];
Response<Students> response = call.execute();
return response.body().getStudents();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
#Override
protected void onPostExecute(List<Students> students) {
}
}
One of the options is to create interface and use as callback.
In async task class :
public class NetworkCall extends AsyncTask<Call, Void, List<Student>> {
public interface NetworkCallback{
void onResponse(List<Students> students);
}
private NetworkCallback callback;
public void setCallback(NetworkCallback callback){
this.callback = callback;
}
#Override
protected List<Students> doInBackground(Call... calls) {
try {
Call<Students> call = calls[0];
Response<Students> response = call.execute();
return response.body().getStudents();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
#Override
protected void onPostExecute(List<Students> students) {
callback.onResponse(students)
}
}
and now in your activity implement the interface and provide to the async task via setter.
public class StudentsActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//.... you setup for activity
NetworkCall networkCall = new NetworkCall();
networkCall.setCallback(new NetworkCall.NetworkCallback() {
#Override
public void onResponse(List<Students> students) {
//update your UI here
}
});
}
}
Based on the Docs onPostExecute runs on the main UI thread so no need to the runOnUiThread and Runnable
you can implement like this:
Your interface:
public interface OnTaskCompleted{
void onTaskCompleted(Object o);
}
Your Activity:
public class YourActivity implements OnTaskCompleted{
// your Activity
#Override
void onTaskCompleted(Object o){
}
And your AsyncTask:
public class YourTask extends AsyncTask<Object,Object,Object>{ //change Object
to required type
private OnTaskCompleted listener;
public YourTask(OnTaskCompleted listener){
this.listener=listener;
}
// required methods
protected void onPostExecute(Object o){
// your stuff
listener.onTaskCompleted(o);
}
}
I am trying to notify the main thread that all Callables executed by a Executor Service have completed.
At the moment I got a splash screen activity showing just an animated image. In the method OnCreate of this activity I load the application data in multithreading. Now I want to execute the goToMainMenu() method without locking the UI Thread.
With the following code as expected the method task.get() stop the UI Thread.
I could accomplish what I want with an Async Task by calling ((ApplicationClass) getApplication()).getApplicationData().LoadApplicationData();
on the doInBackground() method, however mixing up threads inside a Async thread doesn't sound the correct practice for this.
My Application Class:
public class ApplicationClass extends Application {
private ApplicationData applicationData;
public ApplicationData getApplicationData()
{
return applicationData;
}
#Override
public void onCreate()
{
super.onCreate();
applicationData = new ApplicationData(this);
}
}
My Activity:
public class SplashScreenActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
((ApplicationClass) getApplication()).getApplicationData().LoadApplicationData();
goToMainMenu();
}
private void goToMainMenu() {
Intent content = new Intent(SplashScreenActivity.this, ContentActivity.class);
content.putExtra("menu", getString(R.string.nav_title_news));
startActivity(content);
finish();
}
}
My ApplicationData Class:
public final class ApplicationData {
Context c;
//There are more Variables to store work by Callables methods
public ApplicationData(Context context) {
this.c = context;
}
public void LoadApplicationData() throws Exception {
int PROCESSES = 6;
ExecutorService executor = Executors.newFixedThreadPool(PROCESSES);
List<Callable<Void>> callables = Arrays.asList(
new Callable<Void>() {
#Override
public Void call() throws Exception {
LoadEventsLocations(c.getResources().getString(R.string.webserviceeventslocations));
return null;
}
}, new Callable<Void>() {
#Override
public Void call() throws Exception {
LoadTags(c.getResources().getString(R.string.webservicetags));
return null;
}
}, new Callable<Void>() {
#Override
public Void call() throws Exception {
homehtml = LoadHtml(c.getResources().getString(R.string.urlhome), c.getResources().getString(R.string.classarticletext), "home");
return null;
}
}, new Callable<Void>() {
#Override
public Void call() throws Exception {
objhtml = LoadHtml(c.getResources().getString(R.string.urlobjectives), c.getResources().getString(R.string.classarticletext), "obj");
return null;
}
}, new Callable<Void>() {
#Override
public Void call() throws Exception {
contactshtml = LoadHtml(c.getResources().getString(R.string.urlcontacts), c.getResources().getString(R.string.classcontacts), "contacts");
return null;
}
}, new Callable<Void>() {
#Override
public Void call() throws Exception {
commissionhtml = LoadHtml(c.getResources().getString(R.string.urlcommission), c.getResources().getString(R.string.classarticletext), "commission");
return null;
}
});
for (Future<Void> task : executor.invokeAll(callables))
task.get();
executor.shutdown();
}
//There are more methods but keep it simple :)
}
What you guys advise me to do?
I have an async Retrofit-based API call in Android and need to wait with the DB calls until the API call finishes, so that I am sure the proper data gets entered into the DB.
I read that you can use Futures to accomplish this task, however with my current implementation I get a null pointer exception.
Below is the API method:
public Future<Void> postPrintMode(String authorization, final int userid, String deviceuid, final Map payload){
api.postPrintMode(authorization, userid, deviceuid, payload, new Callback<PrintMode>() {
#Override
public void success(PrintMode printMode, Response response) {
if (printMode.get_id() != 0) {
dbOps.writePrintMode(userid, printMode);
bus.getBus().post(new EVTNewPrintMode(printMode));
}
}
#Override
public void failure(RetrofitError retrofitError) {
retrofitError.printStackTrace();
APIUtils.showAPIResponseBody(retrofitError);
}
});
return null;
}
And here the block where I want to ensure that the async code is executed BEFORE I continue to read the DB results.
Future<Void> f = APIExec.getInstance().postPrintMode(IConstants.authorization, IConstants.userId, IConstants.deviceUid, payload);
// here I get the null pointer exception
f.get();
// the code below needs to be executed after the postPrintMode(...) async method;
DBPrintMode printMode = APIDBOps.getInstance().readPrintModeByPrintModeID(6);
assertNotNull("Print Mode does not exist", printMode);
You can make your class that calls public Future<Void> postPrintMode method implement the new Callback<PrintMode> interface. After, you can your postPrintMode from it and pass a reference to itself into the method.
Here is a rough example (code not tested)
class Foo implements Callback<PrintMode> {
Future<Void> f;
public Foo(){
f = APIExec.getInstance().postPrintMode(IConstants.authorization, IConstants.userId, IConstants.deviceUid, this);
}
#Override
public void success(PrintMode printMode, Response response) {
if (printMode.get_id() != 0) {
dbOps.writePrintMode(userid, printMode);
bus.getBus().post(new EVTNewPrintMode(printMode));
}
if (f != null){
f.get();
// the code below needs to be executed after the postPrintMode(...) async method;
DBPrintMode printMode = APIDBOps.getInstance().readPrintModeByPrintModeID(6);
assertNotNull("Print Mode does not exist", printMode);
}
}
#Override
public void failure(RetrofitError retrofitError) {
retrofitError.printStackTrace();
APIUtils.showAPIResponseBody(retrofitError);
}
}
Create a AsyncTaskThread class as below,
public class AsyncTaskThread extends AsyncTask<Void, Void, Void> {
Context context;
Handler myHandler;
public AsyncTaskThread( Context activityContext, Handler handler ) {
this.context = activityContext;
this.myHandler = handler;
}
#Override
protected void onPreExecute() {
// before starting thread you can pre process few things here if needed
}
#Override
protected Void doInBackground(Void... params) {
// do whatever you want to do here like calling your API and return your result
return null;
}
#Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
// after doIn Background this method is called which will set the meesage object and give it back to handler
Message message = new Message();
message.obj = result;
myHandler.sendMessage(message);
}
}
call this async class as,
new AsyncTaskThread(this, new MyHandler()).execute();
and You will have to put this handler class inside the class you are putting above line, depending upon the result you get in handle you can perform further operations,
private class MyHandler extends Handler {
#Override
public void handleMessage(Message msg) {
}
}
I'm trying to implement an Observable/Subscriber with RxJava on the onPostExecute() of an AsyncTask and I don't get how to make the connection.
I create the Observable in the onPostExecute method. I want MyFragment to subscribe to this. How do I set this up?
public class LoadAndStoreDataTask extends AsyncTask<String, Integer, String> {
...
#Override
protected void onPostExecute(String result) {
// create the observable
Observable<String> myObservable = Observable.create(
new Observable.OnSubscribe<String>() {
#Override
public void call(Subscriber<? super String> subscriber) {
subscriber.onNext(result);
subscriber.onCompleted();
}
}
);
myObservable.subscribe(mySubscriber);
}
}
public class MyFragment extends Fragment {
...
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Subscriber<String> mySubscriber = new Subscriber<String>() {
#Override
public void onNext(String s) { System.out.println(s); }
#Override
public void onCompleted() { }
#Override
public void onError(Throwable e) { }
};
}
...
}
Actually RxJava is supposed to replace AsycTask. In fact I can say with confidence that AsyncTask is a subset of RxJava.
In RxJava, a Subscriber would be analogous to AsyncTask.progressUpdate or onPostExecute and Observable to the process in doInBackground. Data are emitted from Observable to Subscriber and any alteration in this stream is done with mapping methods. You probably don't need mapping now so I would reconfigure my RxJava like this:
Observable<String> myObservable = Observable.create(
new Observable.OnSubscribe<String>() {
#Override
public void call(Subscriber<? super String> subscriber) {
try{
String res = ...//your original doInBackground
subscriber.onNext(res);
// onNext would be comparable to AsyncTask.onProgressUpdate
// and usually applies when backgorund process runs a loop
subscriber.onCompleted();
}catch (SomeException e){
// if the process throws an exception or produces a result
// you'd consider error then use onError
subscriber.onError(e);
}
}
}
)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread()) // If subscriber runs on UI thread
.subscribe(new Subscriber<String>() {
#Override
public void onNext(String response) {
// result from Observable.onNext. The methods below correspond
// to their Observable counterparts.
}
#Override
public void onCompleted() {}
#Override
public void onError(Throwable e) {}
});
AndroidSchedulers is available in RxAndroid. To use it add this line to build.gradle :
compile 'io.reactivex:rxandroid:0.24.0'