External AsyncTask class with ProgressDialog [Update: and returning back?]
Solution 1
You were creating the ProgressDialog
with a null context. The following code worked for me.
public class AsyncClass extends AsyncTask<Void, String, Void> {
private Context context;
ProgressDialog dialog;
public AsyncClass(Context cxt) {
context = cxt;
dialog = new ProgressDialog(context);
}
@Override
protected void onPreExecute() {
dialog.setTitle("Please wait");
dialog.show();
}
@Override
protected Void doInBackground(Void... unused) {
SystemClock.sleep(2000);
return (null);
}
@Override
protected void onPostExecute(Void unused) {
dialog.dismiss();
}
}
Solution 2
ok this is what I did as i was using fragments. This is how you call the AsyncTask inside a fragment:
String result=new AsyncClass(getActivity()).execute();
and this is how my AsyncTask outer class looks like:
public class AsyncClass extends AsyncTask<Void, Void, String> {
ProgressDialog pdialog;
public AsyncClass(Context context) {
pdialog = new ProgressDialog(context);
}
@Override
protected void onPreExecute() {
pdialog.setIndeterminate(true);
pdialog.setCancelable(false);
pdialog.setTitle("Loading Feed..");
pdialog.setMessage("Please wait.");pdialog.show();
}
@Override
protected String doInBackground(Void... params) {
String result=null;
//do your task here and generate result String
return result;
}
@Override
protected void onPostExecute(String result) {
if(pdialog.isShowing())
pdialog.dismiss();
}
}
@SSZero thanks great answer, helped a lot.
Solution 3
I would like to answer that follow up question i.e.
I have a follow up question: Using the above code, is it possible to return a value from the onPostExecute method back to the main class, somehow? (Sorry about beeing noobish) I have tried something like this:
String result = new AsyncClass(this).execute();
I did this in my code it worked.
AsyncClass ac=new AsyncClass();
ac.execute("");
String rslt=ac.get();
Call this code wherever you want to.
public class AsynchClass extends AsyncTask <String,Integer,String>
{
public String result=null;
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
}
protected String doInBackground(String... params)
{
// Do all your background task here
return result;
}
@Override
protected void onProgressUpdate(Integer... values) {
}
protected void onPostExecute(String result) {
}
}
droidgren
Updated on June 04, 2022Comments
-
droidgren about 2 years
**Updated: (See below)**I have been looking around for couple of days and can't find a straight answer to this. Some say it possible to some say to accomplish some say it's not. I am getting crazy on this.
What I want is just to have the AsyncTaskTask showing a progressbar an external class. To do this I am passing the context as you can see in the main class. But whatever I try I get
NullPointerException
.Working code examples is appreciated. Thank you
Using Android 2.2 by the way.
main:
import android.app.Activity; import android.os.Bundle; public class AsyncDemo extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); new AsyncClass(this).execute(); } }
AsyncClass.java
import android.app.ProgressDialog; import android.content.Context; import android.os.AsyncTask; import android.os.SystemClock; public class AsyncClass extends AsyncTask<Void, String, Void> { private Context context; ProgressDialog dialog = new ProgressDialog(context); public AsyncClass(Context cxt) { context = cxt; } @Override protected void onPreExecute() { dialog.setTitle("Please wait"); dialog.show(); } @Override protected Void doInBackground(Void... unused) { SystemClock.sleep(2000); return (null); } @Override protected void onPostExecute(Void unused) { dialog.dismiss(); } }
Update: I have a follow up question: Using the above code, is it possible to return a value from the onPostExecute method back to the main class, somehow? (Sorry about beeing noobish) I have tried something like this:
String result = new AsyncClass(this).execute();
and then a method that return back a string. But I can't do that because i got:
Type mismatch: cannot convert from AsyncTask<String,Void,Void> to String
What can I do to tackle this problem? Thanks.