Passing arguments to AsyncTask, and returning results
Solution 1
Change your method to look like this:
String curloc = current.toString();
String itemdesc = item.mDescription;
ArrayList<String> passing = new ArrayList<String>();
passing.add(itemdesc);
passing.add(curloc);
new calc_stanica().execute(passing); //no need to pass in result list
And change your async task implementation
public class calc_stanica extends AsyncTask<ArrayList<String>, Void, ArrayList<String>> {
ProgressDialog dialog;
@Override
protected void onPreExecute() {
dialog = new ProgressDialog(baraj_mapa.this);
dialog.setTitle("Calculating...");
dialog.setMessage("Please wait...");
dialog.setIndeterminate(true);
dialog.show();
}
protected ArrayList<String> doInBackground(ArrayList<String>... passing) {
ArrayList<String> result = new ArrayList<String>();
ArrayList<String> passed = passing[0]; //get passed arraylist
//Some calculations...
return result; //return result
}
protected void onPostExecute(ArrayList<String> result) {
dialog.dismiss();
String minim = result.get(0);
int min = Integer.parseInt(minim);
String glons = result.get(1);
String glats = result.get(2);
double glon = Double.parseDouble(glons);
double glat = Double.parseDouble(glats);
GeoPoint g = new GeoPoint(glon, glat);
String korisni_linii = result.get(3);
}
UPD:
If you want to have access to the task starting context, the easiest way would be to override onPostExecute in place:
new calc_stanica() {
protected void onPostExecute(ArrayList<String> result) {
// here you have access to the context in which execute was called in first place.
// You'll have to mark all the local variables final though..
}
}.execute(passing);
Solution 2
Why would you pass an ArrayList?? It should be possible to just call execute with the params directly:
String curloc = current.toString();
String itemdesc = item.mDescription;
new calc_stanica().execute(itemdesc, curloc)
That how varrargs work, right? Making an ArrayList to pass the variable is double work.
Solution 3
I sort of agree with leander on this one.
call:
new calc_stanica().execute(stringList.toArray(new String[stringList.size()]));
task:
public class calc_stanica extends AsyncTask<String, Void, ArrayList<String>> {
@Override
protected ArrayList<String> doInBackground(String... args) {
...
}
@Override
protected void onPostExecute(ArrayList<String> result) {
... //do something with the result list here
}
}
Or you could just make the result list a class parameter and replace the ArrayList with a boolean (success/failure);
public class calc_stanica extends AsyncTask<String, Void, Boolean> {
private List<String> resultList;
@Override
protected boolean doInBackground(String... args) {
...
}
@Override
protected void onPostExecute(boolean success) {
... //if successfull, do something with the result list here
}
}
Solution 4
I dont do it like this. I find it easier to overload the constructor of the asychtask class ..
public class calc_stanica extends AsyncTask>
String String mWhateveryouwantToPass;
public calc_stanica( String whateveryouwantToPass)
{
this.String mWhateveryouwantToPass = String whateveryouwantToPass;
}
/*Now you can use whateveryouwantToPass in the entire asynchTask ... you could pass in a context to your activity and try that too.*/ ... ...
Bojan Ilievski
Updated on June 20, 2020Comments
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Bojan Ilievski almost 4 years
I have an application that does some long calculations, and I would like to show a progress dialog while this is done. So far I have found that I could do this with threads/handlers, but didn't work, and then I found out about the
AsyncTask
.In my application I use maps with markers on it, and I have implemented the onTap function to call a method that I have defined. The method creates a dialog with Yes/No buttons, and I would like to call an
AsyncTask
if Yes is clicked. My question is how to pass anArrayList<String>
to theAsyncTask
(and work with it there), and how to get back a newArrayList<String>
like a result from theAsyncTask
?The code of the method looks like this:
String curloc = current.toString(); String itemdesc = item.mDescription; ArrayList<String> passing = new ArrayList<String>(); passing.add(itemdesc); passing.add(curloc); ArrayList<String> result = new ArrayList<String>(); new calc_stanica().execute(passing,result); String minim = result.get(0); int min = Integer.parseInt(minim); String glons = result.get(1); String glats = result.get(2); double glon = Double.parseDouble(glons); double glat = Double.parseDouble(glats); GeoPoint g = new GeoPoint(glon, glat); String korisni_linii = result.get(3);
So, as you see, I would like to send the string array list "passing" to the
AsyncTask
, and to get the "result" string array list back from it. And the calc_stanicaAssycTask
class looks like this:public class calc_stanica extends AsyncTask<ArrayList<String>, Void, ArrayList<String>> { ProgressDialog dialog; @Override protected void onPreExecute() { dialog = new ProgressDialog(baraj_mapa.this); dialog.setTitle("Calculating..."); dialog.setMessage("Please wait..."); dialog.setIndeterminate(true); dialog.show(); } protected ArrayList<String> doInBackground(ArrayList<String>... passing) { //Some calculations... return something; //??? } protected void onPostExecute(Void unused) { dialog.dismiss(); }
So my question is how to get the elements of the "passing" array list in the
AsyncTask doInBackground
method (and use them there), and how to return an array list to use in the main method (the "result" array list)? -
Bojan Ilievski over 13 yearsThank you for your answer, but I have one more thing to ask. If I define int min = Integer.parseInt(minim); for example, in the AsyncTask class onPostExecute(), how can I access it from my main class method? When I change it like this, I get "min cannot be resolved" error in the main class method.
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Wroclai over 13 years@Bojan Ilievski: Just make your min variable global.
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VansFannel about 12 yearsI get the following error when I pass an
ArrayList
onAsyncTask.execute
: Type safety: A generic array of ArrayList<String> is created for a varargs parameter. -
Jared Burrows almost 12 yearsThanks so much for posting this!
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JohnK almost 12 yearsI've got a similar question, but for me the result is important. I don't see in your example how
result
gets back to the main method. I just don't get it. Could you please explain? -
Konstantin Burov almost 12 years@JohnK in essense, result never get's to the original method.. it is only available when onPostExecute method runs, usually when the original method returns already. That's why it's called async task.
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JohnK almost 12 years@KonstantinBurov, thanks for your reply! Just to be clear: by "main method" I mean the module/method that initiated
doInBackground
, in your example, the first block of code, specifically the linenew calc_stanica().execute(passing);
. So you pass in data, viapassing
; how do you get data back? If I wanted to get a result back, it sounds like I'd have to store it in a field (or some kind of global variable if the main method is static)... is that right? -
Keith Entzeroth over 11 yearsI strongly agree with Leander here. Anyway to change the correct answer checkmark?