If this is so, why do I get a null pointer exception whenever I call
any method from the UI thread even after creating an instance of that
object? I tried passing the activity as an argument in the constructor
for the AsyncTask:
Activity mParentActivity;
public LoginTask(Context context,Activity act){
this.ctx=context;
this.mParentActivity=act;
}
onPostExecute(..){
mParentActivity.callSomeMethod();
}
I get a NullPointerException when I tried this..
On Mar 8, 8:23 pm, Romain Guy <romain...@android.com> wrote:
> > Where ctx is a context object. I understand now that you can't call
> > methods from the UI thread in the AsyncTask.
>
> You can call method on the UI thread in AsyncTask, that's what it's
> for. But you cannot call method from other classes (like Context)
> unless you have instances of them. This is no different than in any
> other place of your application :)
>
>
>
>
>
>
>
> > On Mar 7, 1:08 am, John Wesonga <johnweso...@gmail.com> wrote:
> >> I figured something out which I thought would work, within my
> >> LoginTask class I created an object which was of the parent activity:
>
> >> Test101 mParentActivity;
>
> >> and then:
>
> >> protected void onPostExecute(String result) {
>
> >> Intent i=new Intent(ctx,SillyActivity.class);
> >> mParentActivity.startActivity(i);
>
> >> }
>
> >> An error is thrown:
>
> >> 03-07 01:04:50.259: ERROR/AndroidRuntime(801): Uncaught handler:
> >> thread main exiting due to uncaught exception
> >> 03-07 01:04:50.319: ERROR/AndroidRuntime(801):
> >> java.lang.NullPointerException
> >> 03-07 01:04:50.319: ERROR/AndroidRuntime(801): at
> >> org.tutorial.test101.tasks.LoginTask.onPostExecute(LoginTask.java:46)
> >> 03-07 01:04:50.319: ERROR/AndroidRuntime(801): at
> >> org.tutorial.test101.tasks.LoginTask.onPostExecute(LoginTask.java:1)
> >> 03-07 01:04:50.319: ERROR/AndroidRuntime(801): at
> >> android.os.AsyncTask.finish(AsyncTask.java:416)
> >> 03-07 01:04:50.319: ERROR/AndroidRuntime(801): at
> >> android.os.AsyncTask.access$300(AsyncTask.java:127)
> >> 03-07 01:04:50.319: ERROR/AndroidRuntime(801): at
> >> android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:428)
> >> 03-07 01:04:50.319: ERROR/AndroidRuntime(801): at
> >> android.os.Handler.dispatchMessage(Handler.java:99)
> >> 03-07 01:04:50.319: ERROR/AndroidRuntime(801): at
> >> android.os.Looper.loop(Looper.java:123)
> >> 03-07 01:04:50.319: ERROR/AndroidRuntime(801): at
> >> android.app.ActivityThread.main(ActivityThread.java:3948)
> >> 03-07 01:04:50.319: ERROR/AndroidRuntime(801): at
> >> java.lang.reflect.Method.invokeNative(Native Method)
> >> 03-07 01:04:50.319: ERROR/AndroidRuntime(801): at
> >> java.lang.reflect.Method.invoke(Method.java:521)
> >> 03-07 01:04:50.319: ERROR/AndroidRuntime(801): at
> >> com.android.internal.os.ZygoteInit
> >> $MethodAndArgsCaller.run(ZygoteInit.java:782)
> >> 03-07 01:04:50.319: ERROR/AndroidRuntime(801): at
> >> com.android.internal.os.ZygoteInit.main(ZygoteInit.java:540)
> >> 03-07 01:04:50.319: ERROR/AndroidRuntime(801): at
> >> dalvik.system.NativeStart.main(Native Method)
>
> >> Stuck again it seems..
>
> >> On Mar 6, 10:57 pm, John Wesonga <johnweso...@gmail.com> wrote:
>
> >> > I just modified my onPostExecute(...) method:
>
> >> > protected void onPostExecute(String result) {
>
> >> > Log.i("LOGGER", "Done...");
> >> > pDialog.dismiss();
> >> > if(result=="success"){
> >> > Toast.makeText(ctx, "complete",
> >> > Toast.LENGTH_LONG).show();
> >> > Intent i=new
> >> > Intent(ctx,SillyActivity.class);
> >> > startActivity(i);
> >> > }else{
> >> > Toast.makeText(ctx, "fail",
> >> > Toast.LENGTH_LONG).show();
> >> > }
>
> >> > super.onPostExecute(result);
> >> > }
>
> >> > ctx is my context
> >> > I noticed that I can't call the startActivity(Intent i) method within
> >> > the AsyncTask, how else would I start an activity from here?
>
> >> > On Mar 6, 10:13 pm, Romain Guy <romain...@android.com> wrote:
>
> >> > > onPostExecute() is invoked on the UI thread so you can use this method
> >> > > to start an Activity. It's pretty much what it's for.
>
> >> > > On Fri, Mar 5, 2010 at 6:29 AM, John Wesonga <johnweso...@gmail.com>
> >> > > wrote:
> >> > > > I have a simple app and I'm using the AsyncTask to test out a
> >> > > > background process, for clearness purposes I've opted to put my
> >> > > > AsyncTask in a separate class rather than in an inner class, which
> >> > > > where my problems begin, this is my AsyncTask
>
> >> > > > package org.tutorial.test101.tasks;
>
> >> > > > import android.app.ProgressDialog;
> >> > > > import android.content.Context;
> >> > > > import android.os.AsyncTask;
> >> > > > import android.util.Log;
>
> >> > > > public class LoginTask extends AsyncTask<String, String, String> {
>
> >> > > > Context ctx;
> >> > > > ProgressDialog pDialog;
>
> >> > > > public LoginTask(Context context){
> >> > > > super();
> >> > > > this.ctx=context;
> >> > > > }
> >> > > > �...@override
> >> > > > protected String doInBackground(String... params) {
> >> > > > Log.i("LOGGER", "Starting...");
> >> > > > try{
> >> > > > Thread.sleep(8000);
> >> > > > }catch(InterruptedException e){
>
> >> > > > }
> >> > > > return null;
> >> > > > }
>
> >> > > > �...@override
> >> > > > protected void onPostExecute(String result) {
>
> >> > > > Log.i("LOGGER", "Done...");
> >> > > > pDialog.dismiss();
> >> > > > //
> >> > > > super.onPostExecute(result);
> >> > > > }
>
> >> > > > �...@override
> >> > > > protected void onPreExecute() {
> >> > > > pDialog=new ProgressDialog(ctx);
> >> > > > pDialog.setTitle("Login");
> >> > > > pDialog.setMessage("doing stuff..");
> >> > > > pDialog.show();
> >> > > > }
>
> >> > > > }
>
> >> > > > What I'd like is that once the task is complete, I do something in
> >> > > > the
> >> > > > UI thread may be start another activity or even display a Toast
> >> > > > saying
> >> > > > activity complete. I know I can't start a new Activity in the
> >> > > > onPostExecute() so I need to start it in the UI thread any idea how I
> >> > > > can do this? This is my Activity that starts the AsyncTask
>
> >> > > > package org.tutorial.test101.activities;
>
> >> > > > import org.tutorial.test101.tasks.LoginTask;
>
> >> > > > import android.app.Activity;
> >> > > > import android.app.Dialog;
> >> > > > import android.content.Context;
> >> > > > import android.os.AsyncTask;
> >> > > > import android.os.Bundle;
> >> > > > import android.util.Log;
> >> > > > import android.view.View;
> >> > > > import android.view.View.OnClickListener;
> >> > > > import android.widget.Button;
>
> >> > > > public class Test101 extends Activity{
> >> > > > private Button btnLogin;
> >> > > > private LoginTask mLoginTask;
> >> > > > private Context context=this;
> >> > > > /** Called when the activity is first created. */
> >> > > > �...@override
> >> > > > public void onCreate(Bundle savedInstanceState) {
> >> > > > super.onCreate(savedInstanceState);
> >> > > > setContentView(R.layout.main);
> >> > > > btnLogin=(Button)findViewById(R.id.btnLogin);
> >> > > > btnLogin.setOnClickListener(new OnClickListener(){
>
> >> > > > public void onClick(View v) {
> >> > > > if(mLoginTask==null){
> >> > > > mLoginTask=new
> >> > > > LoginTask(context);
> >> > > > mLoginTask.execute(null);
> >> > > > }
>
> >> > > > }
>
> >> > > > });
> >> > > > }
>
> >> > > > }
>
> >> > > > --
> >> > > > You received this message because you are subscribed to the Google
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> >> > > > To post to this group, send email to
> >> > > > android-developers@googlegroups.com
> >> > > > To unsubscribe from this group, send email to
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> >> > > > For more options, visit this group at
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>
> >> > > --
> >> > > Romain Guy
> >> > > Android framework engineer
> >> > > romain...@android.com
>
> >> > > Note: please don't send private questions to me, as I don't have time
> >> > > to provide private support. All such questions should be posted on
> >> > > public forums, where I and others can see and answer them
>
> > --
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>
> --
> Romain Guy
> Android framework engineer
> romain...@android.com
>
> Note: please don't send private questions to me, as I don't have time
> to provide private support. All such questions should be posted on
> public forums, where I and others can see and answer them
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