Apparently the Activity you pass is null. And you seem to
misunderstand what the UI thread is. A Context or an Activity is NOT
the UI thread.
On Wed, Mar 10, 2010 at 12:24 AM, John Wesonga <johnweso...@gmail.com> wrote:
> 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
>> >> > > > Groups "Android Developers" group.
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>> >> > > > android-developers@googlegroups.com
>> >> > > > To unsubscribe from this group, send email to
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>> >> > > > For more options, visit this group at
>> >> > > >http://groups.google.com/group/android-developers?hl=en
>>
>> >> > > --
>> >> > > 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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>> > Groups "Android Developers" group.
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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
--
You received this message because you are subscribed to the Google
Groups "Android Developers" group.
To post to this group, send email to android-developers@googlegroups.com
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