Develop Reference

How to show AlertDialog in AsyncTask without leaking Context?

I have the below code working fine to find and read a record in a Room database via an id. Android Studio required adding a try/catch block which I've included below.
Two questions:
Can I leave the if{} section blank in onPostExecute() if there is no Exception?
How do I show an AlertDialog here without leaking contect and without using a hack via WeakReference?
// AsyncTask for reading an existing CardView from the database.
private static class ReadAsyncTask extends AsyncTask<Integer, Void, Quickcard> {
private QuickcardDao asyncTaskDao;
Exception e;
ReadAsyncTask(QuickcardDao dao) {
asyncTaskDao = dao;
}
#Override
public Quickcard doInBackground(final Integer... params) {
Quickcard result;
try {
result = asyncTaskDao.readCardForUpdate(params[0]);
} catch (Exception e) {
this.e = e;
result = null;
}
return result;
}
#Override
protected void onPostExecute(Quickcard quickcard) {
if (e == null) {
// *** Okay to leave this blank? If not, what should go here?
}
else {
// *** How do I show an AlertDialog here with leaking context?
}
}
}

You cannot use a view object while using a thread that operates in background.. U must implement the dialog in the UI thread. When you are implementing the the asynchronous class, in that method you should show the alert dialog. Hope this helps..

This is what I will do to prevent leaks from happening.
private static class showDialog extends AsyncTask<String, String, String> {
private WeakReference<MainActivity> mainActivityWeakReference;
showDialog(MainActivity mainActivity){
this.mainActivityWeakReference = new WeakReference<>(mainActivity);
}
#Override
protected String doInBackground(String... params) {
//do your long long time consuming tasks here.
return "Done";
}
#Override
protected void onPostExecute(String result) {
// execution of result of Long time consuming operation
//Just building an alert dialog to show.
if (mainActivityWeakReference.get() != null){
final MainActivity activity = mainActivityWeakReference.get();
new AlertDialog.Builder(activity).setPositiveButton(android.R.string.yes, new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialogInterface, int i) {
Toast.makeText(activity, "Yes was clicked", Toast.LENGTH_SHORT).show();
}
}).show();
}
}
#Override
protected void onPreExecute() {
}
#Override
protected void onProgressUpdate(String... text) {
}
}

I want to use a progress bar with RxJava like you can with AsyncTask

I want to replace my AsyncTask with RxJava in android. My current AsyncTask goes like this:
public class ProgressBarAsyncTask extends AsyncTask<Void,Void,Void> {
#Override
protected void onPreExecute() {
super.onPreExecute();
ringProgressDialog = ProgressDialog.show(context,"MyProgressBarTitle","Working please wait",true, false);
}
#Override
protected Void doInBackground(Void... void) {
//do work
myTask();
return null;
}
#Override
protected void onPostExecute(Void void) {
super.onPostExecute();
ringProgressDialog.dismiss();
}
}
Here's my RxJava replacement:
public static Observable<Void> getObservable(final Context context,final String... params) {
return Observable.defer(new Func0<Observable<Void>>() {
#Override
public Observable<Void> call() {
return Observable.just(myTask());
}
});
}
public static Subscriber<Void> getSubscriber() {
Subscriber<Void> subscriber = new Subscriber<Void>() {
#Override
public void onCompleted() {
ringProgressDialog.dismiss();
}
#Override
public void onError(Throwable e) {
Log.d(TAG,e.toString());
}
#Override
public void onNext(Void aVoid) {
manipulateData();
}
};
return subscriber;
}
My Activity:
public class MainActivity extends Activity {
private ProgressDialog ringProgressDialog;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
GetNumberObservable.Observable()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread()))
.subscribe(getSubscriber());
}
}
How do I mimic the onPreExecute() method in the AsyncTask where I kick off the progressDialog?

Here is how I would do it:
public final class ProgressOrResult<T> {
final int progress;
final T result;
public ProgressOrResult(int progress, T result) {
this.progress = progress;
this.result = result;
}
}
ProgressDialog ringProgressDialog = ProgressDialog.show(
context, "MyProgressBarTitle", "Working please wait", true, false);
Observable.fromEmitter((Emitter<ProgressOrResult> emitter) -> {
// generate "progress"
int sum = 0;
for (int i = 1; i <= 100; i++) {
sum += i;
emitter.onNext(new ProgressOrResult(i, null));
Thread.sleep(1);
}
// generate "result"
emitter.onNext(new ProgressOrResult(100, sum));
emitter.onComplete();
}, BackpressureMode.BUFFER)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(result -> {
if (pr.result == null) {
ringProgressDialog.setProgress(pr.progress);
} else {
ringProgressDialog.dismiss();
// process the result here
}
}, error -> {
// handle error here
})

In RxJava you have the do operators, that creates Observable
lifecycle events listeners, in your case you want to do something
(update the UI) before the task started, which mean you want the
doOnSubscribe event. (side note it is true with 'cold' Observables
that started thier work when subscrbied to - like your case) Just
beware to call .observeOn(AndroidSchedulers.mainThread())) before
the doOnSubscribe in order to get notified on the mainThread, as
you're updating the UI.
Instead of using both defer and just
return Observable.defer(new Func0<Observable<Void>>() {
#Override
public Observable<Void> call() {
return Observable.just(myTask());
}
});
you can use fromCallable:
Observable.fromCallable(new Callable<Object>() {
#Override
public Object call() throws Exception {
return myTask();
}
})

I am showing progressBar indoOnSubscribe() , hiding in doOnError() and in subscribe().
Please refer to this link for more details.

Shameless Promotion
I've created RxLoading library for that, it can do this and much more,
you can just do something like this:
networkCall().compose(RxLoading.<>create(loadingLayout)).subscribe(...);
it consists out of 2 classes, a custom view (loadingLayout) and RxLoading which is a transformer that glue it all together, you can choose to work with both or either of them.
if you want RxLoading with a simple progress bar you just need to implement an interface and you are done.
you can check more on the GitHub page.

async task does not work properly

Hi i have a function to get users from website database
my function
private void get_users() {
try {
url = "my address";
dbGetData3 = new DbGetData();
new Thread(new Runnable() {
public void run() {
data = dbGetData3.getDataFromDB(url);
runOnUiThread(new Runnable() {
#Override
public void run() {
userha = parseJSON3(data);
}
});
}
}).start();
Toast.makeText(context, "please wait ", Toast.LENGTH_LONG)
.show();
} catch (Exception e) {
toast(9);
}
Now i want add a loading progress bar while fetch data finished.
I use AsyncTask like this:
private class LongOperation extends AsyncTask<String, Void, String> {
protected void onPreExecute() {
progressDialog = new ProgressDialog(Login.this);
progressDialog.setTitle("Processing...");
progressDialog.setMessage("Please wait...");
progressDialog.setCancelable(true);
progressDialog.show();
}
protected String doInBackground(String... params) {
try {
get_users();
} catch (Exception e) {
}
return null;
}
protected void onPostExecute(String result) {
progressDialog.dismiss();
}
}
and i use this code for excute
mytask = new LongOperation();
if (Build.VERSION.SDK_INT>=Build.VERSION_CODES.HONEYCOMB)
mytask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
else
mytask.execute();
imageView.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View arg0) {
onCreate(savedInstanceState);
}
});
but progress dialog dose not show for me (get user worked)
i change my code like this:
if (Build.VERSION.SDK_INT>=Build.VERSION_CODES.HONEYCOMB){
mytask.onPreExecute();
mytask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
}
else
{
mytask.onPreExecute();
mytask.execute();
}
then my progress dialog allways show
i test other code in stackoverflow like
AsyncTask doInBackground does not run
AsyncTask called from Handler will not execute doInBackground
Android SDK AsyncTask doInBackground not running (subclass)
but that not work for me
please help me tankyou

Consdier using a LoaderManager and an AsyncTaskLoader for this sort of stuff.
AsyncTasks are a pain in the ass as because you have to manage their lifecycle with screen-rotations etc. With a LoaderManager all of that is in the past.
Below is an example of a loader which loads a list of "items".
public class ItemsLoader extends AsyncTaskLoader<List<Item>> {
private static final String TAG = "ItemsLoader";
private List<Item> mItems;
private ItemUpdatedReceiver mObserver;
private int mSomeParam;
public static class ItemUpdatedReceiver extends BroadcastReceiver {
private static final String TAG = "ItemLoader";
final ItemsLoader mLoader;
public ItemUpdatedReceiver(ItemsLoader mLoader) {
this.mLoader = mLoader;
// listen for changes to the account we're using
IntentFilter filter = new IntentFilter(GlobalConstants.ACTION_ITEMS_UPDATED);
LocalBroadcastManager.getInstance(mLoader.getContext()).registerReceiver(this, filter);
}
#Override
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
if (GlobalConstants.ACTION_ITEMS_UPDATED.equals(action)) {
mLoader.onContentChanged();
}
}
}
public void setSomeParam(int someParam){
mSomeParam = someParam;
onContentChanged();
}
public ItemsLoader(Context context, int someParam) {
super(context);
mSomeParam = someParam;
onContentChanged();
}
#Override
public List<Item> loadInBackground() {
// do whatever you need to do here
ArrayList<Item> Items = new ArrayList<>();
return Items;
}
/**
* Called when there is new data to deliever to the client.
*
* #param data
*/
#Override
public void deliverResult(List<Item> data) {
if (isReset()) {
// an async query came in while the loader is stopped, we don't need the result
//release resources if needed
onReleaseResources(data);
}
List<Item> oldItems = mItems;
mItems = data;
if (isStarted()) {
// If the Loader is currently started, we can immediately
// deliver its results.
super.deliverResult(mItems);
}
// 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 (oldItems != null) {
onReleaseResources(oldItems);
}
}
#Override
protected void onStartLoading() {
super.onStartLoading();
if (mItems != null) {
// If we currently have a result available, deliver it
// immediately.
deliverResult(mItems);
}
// start listening for changes
if (mObserver == null) {
mObserver = new ItemUpdatedReceiver(this);
}
if (takeContentChanged() || mItems == null) {
// 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<Item> items) {
super.onCanceled(items);
// At this point we can release the resources associated with 'profile'
// if needed.
onReleaseResources(items);
}
#Override
protected void onReset() {
super.onReset();
// Ensure the laoder is stopped
onStopLoading();
// At this point we can release the resources if needed.
if (mItems != null) {
onReleaseResources(mItems);
mItems = null;
}
// Stop monitoring for changes.
if (mObserver != null) {
LocalBroadcastManager.getInstance(getContext()).unregisterReceiver(mObserver);
mObserver = null;
}
}
/**
* Helper function to take care of releasing resources associated
* with an actively loaded data set.
*/
private void onReleaseResources(List<Item> data) {
// For a simple List<> there is nothing to do. For something
// like a Cursor, we would close it here.
}
}
To use this class, in your activity you must extend LoaderManager.LoaderCallbacks> and override the methods:
public Loader<List<Item>> 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.
// start the loading dialog here
return new ItemsLoader(context);
}
public void onLoadFinished(Loader<List<Item>> loader, List<Item>data) {
// do something with your data, hide the progress dialog
}
public void onLoaderReset(Loader<Cursor> loader) {
// set the old data to null
}
To actually start loading:
getLoaderManager().initLoader(LOADER_ID, null, this);

Android - progressdialog not displaying in AsyncTask

I have an android app that I am having trouble with.
Basically the ProgressDialog is not showing at all. I believe this to be a threading issue of some sort but I don't know how to fix it.
I am using ActionBarSherlock with some Fragments. I am also using the new Android DrawerLayout where I have my options on the drawer, which replace a fragment when clicked.
On first load of my app, I want to check the database to see if the inital data has been downloaded. If not, then I go off and begin an AsyncTask to download the data. This SHOULD have a ProgressDialog display during this, but it doesnt.
Can someone see where I am going wrong? Thanks.
MainScreen - The default landing page/fragment when the app opens
public class MainScreen extends SherlockFragment {
public static final String TAG = "MainScreen";
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.activity_main, container, false);
setHasOptionsMenu(false);
ImageView imgLogo = (ImageView) rootView.findViewById(R.id.imgMainScreen);
imgLogo.setOnClickListener(new ButtonHandler(getActivity()));
checkDatabase();
return rootView;
}
private void checkDatabase() {
//Ensure there is data in the database
DBHelper db = new DBHelper(this.getSherlockActivity());
db.checkDatabase();
}
...
}
DBHelper.checkDatabase() - The method that initiates the download
public void checkDatabase() {
if (isEmpty()) {
//Connect to net and download data
NetworkManager nm = new NetworkManager(activity);
if (!nm.downloadData()) {
Toast.makeText(activity, R.string.internetCheck, Toast.LENGTH_SHORT).show();
}
}
}
and finally
NetworkManager.downloadData() - The method that kicks off the AsyncTask:
public boolean downloadData() {
try {
return new HttpConnection(activity).execute().get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
return false;
}
public class HttpConnection extends AsyncTask<Void, Void, Boolean> {
private ProgressDialog progressDialog;
private Activity m_activity;
protected HttpConnection(Activity activity) {
m_activity = activity;
}
#Override
protected void onPreExecute() {
progressDialog = new ProgressDialog(m_activity);
progressDialog.setMessage("Wait ...");
progressDialog.setCancelable(false);
progressDialog.setMax(100);
progressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
progressDialog.show();
super.onPreExecute();
}
#Override
protected Boolean doInBackground(Void... params) {
String[] types = new String[]{"type1", "type2", "type3", "type4", };
StringBuilder sb = new StringBuilder();
for(String type : types) {
sb = new StringBuilder();
if(DBHelper.TYPE4_TABLE.equals(type)) {
InputStream is = activity.getResources().openRawResource(R.raw.dbdata);
BufferedReader reader = new BufferedReader(new InputStreamReader(is));
try {
sb.append(reader.readLine());
} catch (IOException e) {
Toast.makeText(activity.getApplicationContext(), "Error retriveving data", Toast.LENGTH_SHORT).show();
Log.e(Constants.TAG, "Error reading data");
e.printStackTrace();
}
} else {
sb = fetchURLData(Constants.ALL_URL+type);
}
cleanDataAndStore(sb, type);
}
return true;
}
#Override
protected void onPostExecute(Boolean result){
progressDialog.hide();
}
}
Using the above code, all I get is a white screen as the app tries to load, and sometimes an ANR. When the download is done, the fragment loads. So it works fine except for the missing ProgressDialog.
PS, Notice I'm setting the activity in each constructor.
Thanks.

Remove .get() from return new HttpConnection(activity).execute().get(); You are basically locking your UI thread. Once removed it should work as AsyncTasks are expected to work.
The purpose is to be Asynchronous so boolean downloadData() should have a return type of void. If you need to do something with the data then you should implement an interface "listener" and pass it to the AsyncTask.
Example Listener:
class TaskConnect extends AsyncTask<Void, Void, ConnectionResponse> {
private final AsyncTaskListener mListener;
/**
*
*/
public TaskConnect(AsyncTaskListener listener) {
...
mListener = listener;
}
#Override
protected void onPreExecute() {
if (mListener != null) {
mListener.onPreExecute(mId);
}
}
#Override
protected ConnectionResponse doInBackground(Void... cData) {
...
return responseData;
}
#Override
protected void onPostExecute(ConnectionResponse response) {
if (mListener != null) {
mListener.onComplete(response);
} else {
LOG.w("No AsyncTaskListener!", new Throwable());
}
}
}
public interface AsyncTaskListener {
public abstract void onPreExecute(int id);
public abstract void onComplete(ConnectionResponse response);
}

My issue was not the common issue of others where they were calling get() method after execute() method. My issue was the Context I was passing to my AsyncTask method. I have a settingsActivity and I have a ReadMeActivity that calls the asynctask task. Instead of using the context in which is was being called (ReadMeActivity.this) I used the settingsActivity which prevented it from being seen. Once I switched it and passed it the context in which the activity was being called it worked.
Hope it helps someone else.

AsyncTask with ProgressDialog vs orientation change

after few desperate days I have finally created almost working example.
The goal: in onCreate I want to download and parseXML files in AsyncTask, show progress dialog, update UI and close the dialog.
The problem: When orientation changes Activity is restarted and AsyncTask loses reference to it. There are a lot of questions and blogs about it. But I cant find out why this particular solution doesnt work. Or how android handles dialogs in this case.
The state: When I start an app everything is ok. I can rotate the device and I can manually start the task again via menu. BUT after task finishes and I change the orientation again dialogs pops up (as expected) and nothing else happens. No progress change, no dialog dismiss. AsyncTask finishes normally.
The code:
package com.test;
import java.io.*;
import java.net.URL;
import java.net.URLConnection;
import java.util.*;
public class Test extends TabActivity {
DownloadFileAsync task;
ProgressDialog progressDialog;
static final int PROGRESS_DIALOG = 0;
private static Data data;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
/* - Run from different locations bug - */
//http://code.google.com/p/android/issues/detail?id=2373
if (!isTaskRoot()) {
final Intent intent = getIntent();
final String intentAction = intent.getAction();
if (intent.hasCategory(Intent.CATEGORY_LAUNCHER) &&
intentAction != null && intentAction.equals(Intent.ACTION_MAIN)) {
finish();
}
}
/* - /Run from different locations bug */
/* -------------- Tabs ---------------- */
Resources res = getResources();
TabHost mTabHost = getTabHost();
mTabHost.addTab(mTabHost.newTabSpec("overview").setIndicator("MYTAB1",res.getDrawable(R.drawable.ic_tab_home)).setContent(R.id.tab1));
mTabHost.setCurrentTab(0);
/* -------------- /Tabs --------------- */
/* -------------- /Data --------------- */
task = (DownloadFileAsync)getLastNonConfigurationInstance();
if(task!= null) {
task.setActivity(this);
} else {
if(data == null) {
File datafile = this.getFileStreamPath("data.dat");
if(datafile.exists()){
//Log.d("log", "File exists!");
try {
long time = System.currentTimeMillis();
ObjectInputStream obj = new ObjectInputStream(new FileInputStream(datafile));
data = (Data)obj.readObject();
obj.close();
Log.d("time", "loaded in:"+(System.currentTimeMillis()- time));
if(data.isUpToDate() || !isOnline()){
update();
}
} catch (Exception e) {
e.printStackTrace();
datafile.delete();
data = null;
}
//Log.d("log", "Passed?");
}
}
/* DEBUG if(data == null || !data.isUpToDate())*/ this.synchronize();
}
/* -------------- /Data --------------- */
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
menu.add("Synchronize").setIcon(R.drawable.ic_menu_refresh);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
synchronize();
return super.onOptionsItemSelected(item);
}
#Override
public Object onRetainNonConfigurationInstance() {
if(task != null) task.setActivity(null);
return(task);
}
protected Dialog onCreateDialog(int id) {
switch (id) {
case PROGRESS_DIALOG:
progressDialog = new ProgressDialog(this);
progressDialog.setMessage("Aktualizuji ...");
progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
progressDialog.setCancelable(false);
//progressDialog.show();
return progressDialog;
default:
return null;
}
}
public void update() {
}
private void onTaskCompleted() {
task = null;
dismissDialog(PROGRESS_DIALOG);
Log.d("tok","Task.onComplete");
update();
}
public void synchronize(){
if(isOnline()) {
showDialog(PROGRESS_DIALOG);
progressDialog.setProgress(0); // <-- this is the last time progressDialog updates
task = new DownloadFileAsync(this);
task.execute();
}
}
public boolean isOnline() {
ConnectivityManager cm =
(ConnectivityManager) getSystemService(WaspActivity.CONNECTIVITY_SERVICE);
NetworkInfo netInfo = cm.getActiveNetworkInfo();
if (netInfo != null && netInfo.isConnectedOrConnecting()) {
return true;
}
return false;
}
private static class DownloadFileAsync extends AsyncTask<String, String, String> {
private Data tempData;
private Test activity;
private int progress = 0;
private File metafile;
private File tempDir;
private FileOutputStream fos;
public DownloadFileAsync(Test activity) {
this.setActivity(activity);
... some more init ...
}
public void setActivity(Test activity) {
this.activity = activity;
}
#Override
protected void onPreExecute() {
super.onPreExecute();
tempData = new Data();
}
#Override
protected String doInBackground(String... aurl) {
try {
... some heavy load ...
//this.progress = someValue;
} catch (Exception e) {
Log.d("Error", "Error while processing files. Code:"+e.getMessage());
e.printStackTrace();
}
//Log.d("time","Task "+(System.currentTimeMillis() - time));
return null;
}
protected void onProgressUpdate(String... progress) {
if(activity != null) activity.progressDialog.setProgress(this.progress);
}
#Override
protected void onPostExecute(String unused) {
data = tempData;
tempData = null;
if(activity != null) {
activity.onTaskCompleted();
activity = null;
}
}
}
}

Yesterday, I wrote a blog post which describes handling configuration changes using retained Fragments.
The TL;DR is to use host your AsyncTask inside a Fragment, call setRetainInstance(true) on the Fragment, and report the AsyncTask's progress/results back to it's Activity through the retained Fragment.

add this to Test activity in manifest
android:configChanges="orientation|keyboardHidden"></activity>
and put this in your test class
#Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
}

Put android:screenOrientation="portrait" in your <activity /> tag of manifest file.
After doing that, put these lines in protected void onPreExecute() method of asyncTask:
dialog.setMessage("Please wait.....");
dialog.setIndeterminate(true);
dialog.setCancelable(false);
dialog.show();