I am working on Android AsyncTask, I wish to make a progress bar during my program is loading. Here's how I make it.
A class is declared here...
private ArrayList<String> result1 = new ArrayList<String>(); //class variable
onCreate()
{
Some stuff here...
new ATask().execute();
for (int i = 0; i <result1.size();i++)
{
output = output +result1.get(i) + "\n\n";
}
textView.setText(output);
}
private void do0()
{
ArrayList<Sentence> result = new ArrayList<Sentence>();
ArrayList<String> result2 = new ArrayList<String>();
result = do1("link", true); //just some function I am working
result1 = do2(result,10);//do2 return ArrayList<String>
}
private class ATask extends AsyncTask<String, Void, String>{
private ProgressDialog progress = null;
#Override
protected String doInBackground(String... params) {
do0();
return null;
}
#Override
protected void onCancelled() {
super.onCancelled();
}
#Override
protected void onPostExecute(String result) {
progress.dismiss();
//adapter.notifyDataSetChanged();
super.onPostExecute(result);
}
#Override
protected void onPreExecute() {
progress = new ProgressDialog(ReadWebPage.this);
progress.setMessage("Doing...");
progress.setProgressStyle(ProgressDialog.STYLE_SPINNER);
progress.show();
super.onPreExecute();
}
#Override
protected void onProgressUpdate(Void... values) {
super.onProgressUpdate(values);
}
};
My intention is that, while the progress bar is loading, it will finish the do0() and modify result1, then my oncreate can use that result1 to display in it's TextView. However my TextView is always empty in this setting. So I move the
for (int i = 0; i <result1.size();i++)
{
output = output +result1.get(i) + "\n\n";
}
textView.setText(output);
into the do0() (right after the result1 = do2()), but then the program will crash. I am not familiar with these thread settings, thanks for your help in advance.
You'll be better served with a thread that holds a Handler object that was initialized on the main thread. Using the handler, you can post() little snippets to be executed on a main thread - like update a progress bar. You can do the same Handler trick from the AsyncTask, but IMHO threads are cleaner.
Said snippets should be implemented as Runnables. Feel free to use a nested anonymous class one-liner.
The problem is with the design of your code. AsyncTask happens asynchronously, so as soon as you call execute on your AsyncTask the rest of your onCreate will execute immediately. AsyncTask will essentially run on a new thread and execute in parallel with your Activity.
What I think you want is to set your TextView in the onPostExecute method of your AsyncTask. onPostExecute gets called after doInBackground is finished.
Also, it is important to keep in mind that doInBackground happens on a background thread, so you cannot make changes to your Activity's UI from code within it. onPre/PostExecute run on the UI thread, so you can make UI changes there, but any code within those methods will also block the UI.
Related
i have problem with some kind a endless loop with AsyncTask..
this is my method with AsyncTask in a fragment class
public AsyncTask<Void, Void, Void> refreshTask = new AsyncTask<Void, Void, Void>() {
#Override
protected Void doInBackground(Void... params) {
Looper.prepare();
System.out.println("UŠAO SAM U DO IN BACKGRASD");
Ponuda.deleteAll();
ArrayList<Ponuda> novaLista= new ArrayList<Ponuda>();
novaLista= (ArrayList<Ponuda>) Ponuda.getAll();
System.out.println("PONUDE: "+ novaLista.size());
((MainActivity)getActivity()).loadData();
Looper.loop();
System.out.println("asdasd"+ Looper.myLooper());
return null;
}
#Override
protected void onPostExecute(Void Void) {
System.out.println("UŠAO SAM U DO IN Post");
mSwipeRefreshLayout.setRefreshing(false);
ArrayList<Ponuda> novaLista= new ArrayList<Ponuda>();
novaLista= (ArrayList<Ponuda>) Ponuda.getAll();
System.out.println("PONUDE: "+ novaLista.size());
RVAdapter adapter = new RVAdapter(novaLista,getContext());
rv.setAdapter(adapter);
super.onPostExecute(Void);
}
};
#Override
public void onRefresh() {
System.out.println("Refreshana je stranica");
refreshTask.execute();
}`
and this is the method that i call from fragment
public void loadData(){
System.out.println("Poziva se funkcija za dohvat podataka");
DataLoader dataLoader;
dataLoader = new WebServiceDataLoader();
if(Ponuda.getAll().isEmpty() || Grad.getAll().isEmpty()){
System.out.println("Dohvaćamo web podatke");
Toast.makeText(this, "Dohvaćamo podatke s weba", Toast.LENGTH_LONG).show();
dataLoader = new WebServiceDataLoader();
} else {
System.out.println("Dohvaćamo lokalne podatke");
Toast.makeText(this, "Dohvaćamo podatke lokalno", Toast.LENGTH_LONG).show();
dataLoader = new DatabaseDataLoader();
}
dataLoader.loadData(this);
System.out.println("asdasdasd");
}
When i debug, the program runs this function and go to fragment inicialization and then go to a endless loop. First it go to ActivityThread class, then to Handler class, then to Looper class it repeat thoose classes again and again. Can somebody please help me?
The problem is the use of the Looper within the AsyncTask's doInBackground() method. AsyncTask is not a generic threading mechanism: it is intended to do short-lived things on a background worker thread which is managed by the system. Your doInBackground() method should not block indefinitely, loop forever, etc. The Looper class is normally used by threads which are going to use a message queue in Android, which allow you to attach Handler objects to them.
This article will help clarify how AsyncTask works: http://po.st/Cei3m2
I'm currently working on my first Android application.
The application accesses a database to get some informations that I want to print on the screen. To send requests and get answers on the network, I need to use a new thread (I'll name it "N thread"), different from the UI Thread. This part is ok.
Now, I want to modify the variable eventList to get the values stored in a collection, in the N thread.
public class MainActivity extends AppCompatActivity {
public List<Event> eventList = null;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
/* I fill the list in an other thread */
new Thread(new Runnable() {
public void run(){
eventList = new WebService().getEvents(); //returns a list
}
// if I check here, eventList contains elements
}).start();
/* I check the result */
TextView respView = (TextView) findViewById(R.id.responseView);
if(eventList != null)
{
respView.setText("Ok");
} else {
respView.setText("Not ok");
}
...
}
The problem is : eventList is not modified. How can modify this variable and print it from the UI thread ?
Thank you for your help.
You can use runOnUiThread function or Handler to update UI from other thread. I suggest you reading the below tutorial first: AndroidBackgroundProcessing
Try this
new AsyncTask<Void, Void, Void>() {
#Override
protected Void doInBackground(Void... params)
{
eventList = new WebService().getEvents();
runOnUiThread(new Runnable() {
#Override
public void run() {
TextView respView = (TextView) findViewById(R.id.responseView);
if(eventList != null)
{
respView.setText("Ok");
} else {
respView.setText("Not ok");
}
}
});
}
}.execute();
private class EventsDownloader extends AsyncTask<Void, Void, Void> {
protected Long doInBackground(Void... params) {
eventList = new WebService().getEvents()
}
protected void onPostExecute(Void result) {
TextView respView = (TextView) findViewById(R.id.responseView);
if(eventList != null)
{
respView.setText("Ok");
} else {
respView.setText("Not ok");
}
}
}
This AsyncTask does what you want, the doInBackground runs on a thread and the 'onPostExecute' runs on the UI thread, and it's only called after the doInBackground finishes. This class is "managed" by the OS. To run it you just need to instantiate it and call 'execute'. I recommend doing something like this
The thing with your code is that the thread runs at the same time as the rest of your code (the calls to the setText), this means when it runs the setText the Thread is still getting the events.
ISSUE/ERROR:
I'm struggling to pass a variable from a doInBackground method into my OnCreate(). I honestly can't believe I'm having so much issues with this.
OBJECTIVE:
Pass a String from AsyncTask method within doInBackground to OnCreate, I want to pass a String to a Textview. And setTextView with the String.
MY UNDERSTANDING:
I have tired creating simple methods within the doInBackground & AsyncTask method and call it in my onCreate(). However the variable is always null. I believe I am miss understanding an aspect of onCreate().
Main Activity: - I want to set variable 'ValueNeeded' in textView
public class OutboxActivity extends ListActivity {
….
…
public void onCreate(Bundle savedInstanceState) {
….
//AsyncTask method
new LoadOutbox().execute();
textView = (TextView) findViewById(R.id.textView6);
textView.setText("ValueNeeded);
Log.d("response", "TOUR NAME: " + ValueNeeded) );
…….
AsyncTask - contains doInBackground
class LoadOutbox extends AsyncTask<String, String, String>
{
/**
* Before starting background thread Show Progress Dialog
* */
#Override
protected void onPreExecute() {
super.onPreExecute();
….
}
doInBackground - String ValueNeeded is the variable I need passed to onCreate()
protected String doInBackground(String... args)
{
..CODE THAT GETS VALUE IS IN HERE...
//ValueNeeded Is
ValueNeeded = c.getString(TAG_TOUR);
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
You have to do it in onPostExecute, not in doInBackground. Just put into onPostExecute textView.setText("ValueNeeded);
Your problem is not "understanding an aspect of onCreate()" but "understanding an aspect of AsyncTask"
Your onCreate needs to be quick. The point of the AsyncTask is to do stuff in another thread so the onCreate can run.
Implement onPostExecute(...) and have that fill in the result. Your onCreate probably needs to have some sort of "Loading..." message to indicate to the user you're getting the data.
protected String doInBackground(String... args) {
..CODE THAT GETS VALUE IS IN HERE...
//ValueNeeded Is
ValueNeeded = c.getString(TAG_TOUR);
// return your value needed here
return ValueNeeded;
}
protected void onPostExecute(String result) {
super.onPostExecute(result);
// this result parameter has the value what you return in doInBackground
// now it has valueNeeded
// set that value to your textview
textView.setText("ValueNeeded);
}
I have an Android application with an AsyncTask which is responsible for downloading a file from the internet. This AsyncTask is executed when clicking on an item in a Listview. So I have a custom adapter and in the OnItemClickListener of the Listview, I start the download and execute the AsyncTask.
Now, my adapter contains the following code to start the AsyncTask named FileDownloader:
#Override
public void onClick(View view) {
try {
FileDownloader fd = new FileDownloader(activity);
// some irrelevant code here
String filepath = fd.execute("http://myurl.com/img.png", PDFFileName, GameHistoryAdapter.this.gameInfo.toString()).get();
}
catch(Exception e) { e.printStackTrace(); }
}
Activity is a private field that is passed to the adapter in the constructor of the adapter:
public GameHistoryAdapter(Activity a, int selectedIndex) {
this.activity = a;
}
The FileDownloader class contains an OnPreExecute method where I want to show the progress dialog on the activity:
#Override
protected void onPreExecute() {
super.onPreExecute();
dialog = new ProgressDialog(activity);
dialog.setMessage("Downloading...");
dialog.setIndeterminate(true);
dialog.setCancelable(true);
dialog.show();
}
But whatever I try, the dialog does not appear. When I create an alert dialog in the OnPostExecute method of the AsyncTask, the dialog will show.
#Override
protected void onPostExecute(String res)
{
super.onPostExecute(res);
dialog.hide();
new AlertDialog.Builder(activity)
.setTitle(activity.getString(R.string.save_pdf_title_text))
.setMessage(activity.getString(R.string.save_pdf_text) + PDFFileName)
.setPositiveButton(activity.getString(R.string.close_text), null)
.setIcon(android.R.drawable.ic_dialog_info)
.show();
}
Does anyone know why the dialog is not appearing on my activity?
Does anyone know why the dialog is not appearing on my activity?
Yes, the following line of code...
String filepath = fd.execute("http://myurl.com/img.png", PDFFileName, GameHistoryAdapter.this.gameInfo.toString()).get();
Don't EVER use the get() method of AsyncTask. It will block the main / UI thread and makes the whole point of an AsyncTask redundant. In other words get() turns it into a synchronous process instead of an asynchronous one.
The fact you can show a dialog in onPostExecute(...) is simply because it will be called after the blocking call to get() has returned. This means the main / UI thread will no longer be frozen (blocked) and UI updates can be made once again.
Remove get() from your call to execute(...) and instead just use...
fd.execute("http://myurl.com/img.png", PDFFileName, GameHistoryAdapter.this.gameInfo.toString());
...then in your onPostExecute(...) method set you filepath variable to what it should be.
I don't know who added the get() method to AsyncTask but if I ever find them I'll have some serious words to say. It has little or no use and causes a lot of people a lot of confusion.
I'm writing an app that at many points will attempt to retrieve account information from a website. I'd like to write a single function ("getAccount()") to do the following:
Show a ProgressDialog
Make the call to the website
Wait for a response
Clear the ProgressDialog
Return control to the calling function after the first four steps are done
I'm not having a problem with getting the data from the page; the problem I have is with the whole "show dialog / wait for completion / return control to the calling function" portion. Either the ProgressDialog doesn't show at all, or the function returns to the caller immediately after making the data request from the site, without giving it enough time to retrieve the data.
Any help would be most appreciated.
EDIT: I'm adding a bit of code below for what I have with AsyncTask. Notice that I have the line MsgBox("done") inside grabURL(); this is simply a Toast call. When I run this code, "done" pops up while the HTTP request is still being made. This MsgBox line only exists so I can see if grabURL is properly waiting for GrabURL to finish (which it isn't).
public void grabURL() {
new GrabURL().execute();
MsgBox("done");
}
private class GrabURL extends AsyncTask<String, Void, Void> {
private ProgressDialog Dialog = new ProgressDialog(MyContext);
protected void onPreExecute() {
Dialog.setTitle("Retrieving Account");
Dialog.setMessage("We're retrieving your account information. Please wait...");
Dialog.show();
}
protected Void doInBackground(String... urls) {
try {
// Get account info from the website
String resp = GetPage(ThePage); // I have this classed out elsewhere
// Some other code that massages the data
AccountRetrievalSuccess = true;
} catch (Exception e) {
AccountRetrievalSuccess = false;
}
return null;
}
protected void onPostExecute(Void unused) {
Dialog.dismiss();
}
}
The message box done appears because AsyncTask is using a separate thread(s) to run doInBackground. The call to execute does NOT block. You could move message box done to onPostExecute following the call to dismiss. Tip. You may want to call progress.cancel in onPause or you may get unwanted behaviour on orientation change. Finally, if you are retrieving info in doInBackground, consider returning the info in doInBackground. The info will be passed to onPostExecute. So if the info is object MyInfo consider:
private class GrabURL extends AsyncTask<String, Void, MyInfo> {
Can't say for sure without seeing some code but sounds like you are making a asynchronous call to the website when you want to make a synchronous call (which will block and wait for return data) to the website instead.
You want to use an AsyncTask, generate a non-user-cancellable ProgressDialog in the onPreExecute, do your work in doInBackground, and dismiss it in onPostExecute.
Something like this:
public class MyApp extends Activity
{
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// blah blah blah
URL url;
try
{
url = new URL("http://example.com");
new MyTask().execute(url);
}
catch (MalformedURLException e)
{
}
}
protected void doSomeStuff()
{
// stuff to do after the asynctask is done
}
protected void throwAWobbly()
{
// stuff to do if you didn't get the data
}
// inner class to do the data getting off the UI thread,
// so android doesn't "not responding" kill you
private class MyTask extends AsyncTask<URL, Void, Boolean>
{
private ProgressDialog dialog;
private boolean gotData = false;
protected void onPreExecute()
{
// create a progress dialog
dialog = ProgressDialog.show(MyApp.this, "",
"Doing stuff. Please wait...", false, false);
}
protected Boolean doInBackground(URL... urls)
{
// get your data in here!
return gotData;
}
protected void onPostExecute(Boolean result)
{
// get rid of the progress dialog
dialog.dismiss();
if (true == result)
{
// got all data!
doSomeStuff();
}
else
{
// oops!
throwAWobbly();
}
}
}
}