It is stated in d.android.com for onPreExecute() that it runs on the UI thread before doInBackground(Params...)
so it should easily access the TextView
and perform setText()
method from the Activity
from which it was executed()
.
But here in the below codes the loading
TextView is privately declared inside the class SplashScreen
that extends Activity . Inside the onCreate()
it is linked with the TextView widget of the UI. But when AsyncTask
extended class Atom
the function onPreExecute()
is executed which throws a NullPointerExcepction
for the statement loading.setText("Loading...");
executed inside it.
Here the code
public class SplashScreen extends Activity implements AnimationListener{
...
TextView loading=null;
...
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.splash_screen);
try {
a = (Atom) new Atom().execute(null,null,null);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
finish();
}
...
loading = (TextView) findViewById(R.id.textView2);
....
}
public class Atom extends AsyncTask<RSSFeed, Void, RSSFeed>{
private RSSReader reader;
private RSSFeed feed = null;
private String uri = "http://website.com/feed/";
@Override
protected void onPreExecute() {
super.onPreExecute();
//------------problem----area-------------------
loading.setText("Loading...");
//------------problem----area-------------------
}
@Override
protected RSSFeed doInBackground(RSSFeed... arg0) {
reader = new RSSReader();
try {
feed = reader.load(uri);
Log.d("rss", feed.getTitle());
} catch (RSSReaderException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return feed;
}
@Override
protected void onPostExecute(RSSFeed result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
prg.cancel();
t(result.getTitle().toString());
}
}
}
The stack:
03-09 10:50:12.793: W/System.err(14214): java.lang.NullPointerException
03-09 10:50:12.813: W/System.err(14214): at in.edu.ss.er.splash.SplashScreen$Atom.onPreExecute(SplashScreen.java:158)
03-09 10:50:12.827: W/System.err(14214): at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586)
03-09 10:50:12.833: W/System.err(14214): at android.os.AsyncTask.execute(AsyncTask.java:534)
03-09 10:50:12.833: W/System.err(14214): at in.edu.ss.er.splash.SplashScreen.onCreate(SplashScreen.java:45)
Try to initialize TextView
before executing asyntask
. Like following.
try {
loading = (TextView) findViewById(R.id.textView2);
a = (Atom) new Atom().execute(null,null,null);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
finish();
}
I don't know this is correct or not, This my guessing, So, Please let me know what happened.
Thanks
just initialize your text view before calling AsyncTask. do something like this
loading = (TextView) findViewById(R.id.textView2);
try {
a = (Atom) new Atom().execute(null,null,null);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
finish();
}
You have to initialize your textview before then call asynctask. Change your code into following-
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.splash_screen);
loading = (TextView) findViewById(R.id.textView2);
try {
a = (Atom) new Atom().execute(null,null,null);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
finish();
}
}
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