NullPointerException while calling AsyncTask.onPreExecute()

Question

I am new to this site. I have an error with my AsyncTask and my android program... this is the first async task that I have written.

The main Class called SocialApp.java

@Override
public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    TextView t = (TextView) this.findViewById(R.id.textView1);       

    HTMLParser task = new HTMLParser();
    task.setTextView(t);
    task.execute();        
}

A basic AsyncTask

public class HTMLParser extends AsyncTask<Void, Void, Boolean> {

    TextView t;
    String title = "error";

    public void setTextView(TextView t){
        this.t = t;
    }

    @Override
    protected void onPreExecute() {
        t.setText(title);
    }

    @Override
    protected Boolean doInBackground(Void ... arg0) {
        t.setText(title);
    }

    @Override
    protected void onPostExecute(Boolean result) {
        t.setText(title);
    }
}

Resulting in this

12-15 12:34:11.808: E/AndroidRuntime(590):  at cv.mk.android.utapp.HTMLParser.onPreExecute(HTMLParser.java:24)
12-15 12:34:11.808: E/AndroidRuntime(590):  at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:561)
12-15 12:34:11.808: E/AndroidRuntime(590):  at android.os.AsyncTask.execute(AsyncTask.java:511)
12-15 12:34:11.808: E/AndroidRuntime(590):  at cv.mk.android.utapp.SocialApp.onCreate(SocialApp.java:26)
12-15 12:34:11.808: E/AndroidRuntime(590):  at android.app.Activity.performCreate(Activity.java:4465)
12-15 12:34:11.808: E/AndroidRuntime(590):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
12-15 12:34:11.808: E/AndroidRuntime(590):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1919)
12-15 12:34:11.808: E/AndroidRuntime(590):  ... 11 more
12-15 12:34:19.666: D/dalvikvm(609): GC_FOR_ALLOC freed 33K, 3% free 9890K/10179K, paused 215ms
12-15 12:34:19.677: I/dalvikvm-heap(609): Grow heap (frag case) to 11.363MB for 1700016-byte allocation
12-15 12:34:19.747: D/dalvikvm(609): GC_CONCURRENT freed <1K, 3% free 11549K/11847K, paused 3ms+12ms
12-15 12:34:19.967: D/dalvikvm(609): GC_CONCURRENT freed 1K, 2% free 12079K/12231K, paused 2ms+3ms
12-15 12:34:20.037: D/dalvikvm(609): GC_FOR_ALLOC freed 1K, 2% free 12298K/12487K, paused 24ms
12-15 12:34:20.277: D/AndroidRuntime(609): Shutting down VM
12-15 12:34:20.277: W/dalvikvm(609): threadid=1: thread exiting with uncaught exception (group=0x409961f8)
12-15 12:34:20.277: D/dalvikvm(609): GC_CONCURRENT freed 1K, 1% free 13063K/13191K, paused 3ms+3ms
12-15 12:34:20.287: E/AndroidRuntime(609): FATAL EXCEPTION: main
12-15 12:34:20.287: E/AndroidRuntime(609): java.lang.RuntimeException: Unable to start activity ComponentInfo{cv.mk.android.utapp/cv.mk.android.utapp.SocialApp}: java.lang.NullPointerException
12-15 12:34:20.287: E/AndroidRuntime(609):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1955)
12-15 12:34:20.287: E/AndroidRuntime(609):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
12-15 12:34:20.287: E/AndroidRuntime(609):  at android.app.ActivityThread.access$600(ActivityThread.java:122)
12-15 12:34:20.287: E/AndroidRuntime(609):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
12-15 12:34:20.287: E/AndroidRuntime(609):  at android.os.Handler.dispatchMessage(Handler.java:99)
12-15 12:34:20.287: E/AndroidRuntime(609):  at android.os.Looper.loop(Looper.java:137)
12-15 12:34:20.287: E/AndroidRuntime(609):  at android.app.ActivityThread.main(ActivityThread.java:4340)
12-15 12:34:20.287: E/AndroidRuntime(609):  at java.lang.reflect.Method.invokeNative(Native Method)
12-15 12:34:20.287: E/AndroidRuntime(609):  at java.lang.reflect.Method.invoke(Method.java:511)
12-15 12:34:20.287: E/AndroidRuntime(609):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
12-15 12:34:20.287: E/AndroidRuntime(609):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
12-15 12:34:20.287: E/AndroidRuntime(609):  at dalvik.system.NativeStart.main(Native Method)
12-15 12:34:20.287: E/AndroidRuntime(609): Caused by: java.lang.NullPointerException
12-15 12:34:20.287: E/AndroidRuntime(609):  at cv.mk.android.utapp.HTMLParser.onPreExecute(HTMLParser.java:24)
12-15 12:34:20.287: E/AndroidRuntime(609):  at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:561)
12-15 12:34:20.287: E/AndroidRuntime(609):  at android.os.AsyncTask.execute(AsyncTask.java:511)
12-15 12:34:20.287: E/AndroidRuntime(609):  at cv.mk.android.utapp.SocialApp.onCreate(SocialApp.java:26)
12-15 12:34:20.287: E/AndroidRuntime(609):  at android.app.Activity.performCreate(Activity.java:4465)
12-15 12:34:20.287: E/AndroidRuntime(609):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
12-15 12:34:20.287: E/AndroidRuntime(609):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1919)
12-15 12:34:20.287: E/AndroidRuntime(609):  ... 11 more

I have tried everything and I am really confused as to what is going on here...

Thank you for our time and effort.

instead of `t.setText(title);` inside the async task, try to create a method on your activity to do that, and call that method on your async task — SERPRO, Dec 15 '11 at 18:45
so I have to send in the instance of SocialApp into the AsyncTask? — Mathew Kurian, Dec 15 '11 at 18:46
You are getting a NullPointerException, are you sure the TextView is initialized correctly? — , Dec 15 '11 at 18:48
no you can access your object with `SocialApp.this` for istance `SocialApp.this.findViewById(View v)` — pna, Dec 15 '11 at 18:49
@pna: i just added this code into my SocialApp public void setText(String g){ ((TextView) this.findViewById(R.id.textView1)).setText(g); } — Mathew Kurian, Dec 15 '11 at 18:53

score 0 · Accepted Answer · edited May 23 '17 at 12:11

0

You can't call t.setText in the doInBackground. That method is run in a different thread so it cannot update the UI. Only things in the UI thread can do that. So, during processing if ou want to update the UI, you must call publishProgress, then the UI thread will call onProgressUpdate, there you can update the UI.

See this thread for a good explanation:

UpdateUI from AsyncTask

While this is still valid, I missed the NullPointer exception. t is probably not getting initialized as was stated above.

edited May 23 '17 at 12:11

Community

1
1

answered Dec 15 '11 at 18:49

Kaediil

5,465
2
21
20

when I set the textView with just lets say "hello" before the super.onCreate(savedInstanceState); setContentView(R.layout.main); is called...it works fine :D...but asynctask messes it up – Mathew Kurian Dec 15 '11 at 18:57
would you be kind enough to remotely use my computer and see whats wrong? – Mathew Kurian Dec 15 '11 at 19:10
thank you guys...i got the error... it wasnt initialized correctly – Mathew Kurian Dec 15 '11 at 19:18

score 0 · Answer 2 · answered Dec 15 '11 at 18:53

0

Put the asynctask inside the activity, like this:

public class HTMLParser extends AsyncTask<Void, Void, Boolean> {

String title = "error";

public void setTextView(TextView t){
    ((TextView) SocialApp.this.findViewById(R.id.yourtextview)).setText(title);
}

@Override
protected void onPreExecute() {

    ((TextView) SocialApp.this.findViewById(R.id.yourtextview)).setText(title);

}

@Override
protected Boolean doInBackground(Void ... arg0) {
    ((TextView) SocialApp.this.findViewById(R.id.yourtextview)).setText(title);
}

@Override
protected void onPostExecute(Boolean result) {
    ((TextView) SocialApp.this.findViewById(R.id.yourtextview)).setText(title);


}
}

answered Dec 15 '11 at 18:53

Noureddine AMRI

2,942
1
21
28

@Noureddine....it says "No enclosing instance of the type SocialApp is accessible in scope" – Mathew Kurian Dec 15 '11 at 18:56
Then the activity's name is not SocialApp. Change SocialApp.this.findViewById to The_name_of_enclosing_activity.this.findViewById – Noureddine AMRI Dec 15 '11 at 18:59
@Nourreddine...it says public class SocialApp extends Activity { – Mathew Kurian Dec 15 '11 at 19:05
thank you guys...i got the error... it wasnt initialized correctly – Mathew Kurian Dec 15 '11 at 19:17

NullPointerException while calling AsyncTask.onPreExecute()

2 Answers2