Question

I have managed to use an Asynctask with an indeterminate progress bar during screen rotation. Asynctask starts only once, progress bar is restored on rotation just as I wanted.

I have different layouts for portrait and layout orientations. Layouts include a button and a textview. The size and text color of textview in layout-land is different. And the orientation is landscape.

The problem is when I rotate the screen while asynctask is running, it cant update the textview in onPostExecute method. When I rotate, it recreates the activity with layout-land file. But why I cant update my Textview?

layout\activity_main.xml:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" 
    android:orientation="vertical">

    <Button 
        android:text="Start"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="startClicked"
        />
    <TextView
        android:id="@+id/hello"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world"
        tools:context=".MainActivity" />

</LinearLayout>

layout-land\activity_main.xml:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" 
    android:orientation="horizontal">

    <Button 
        android:text="Start"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="startClicked"
        />
    <TextView
        android:textSize="36dp"
        android:textColor="#ff0000"
        android:id="@+id/hello"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world"
        tools:context=".MainActivity" />

</LinearLayout>

MainActivity.java:

package com.example.asynctaskconfig;

import android.app.Activity;
import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

    public class MainActivity extends Activity {
        static String data;
        static ProgressDialog pd;
        MyAsyncTask task;
        TextView tv;

        @Override
        public void onCreate(Bundle icicle) {
            super.onCreate(icicle);
            setContentView(R.layout.activity_main);

            tv = (TextView) findViewById(R.id.hello);

            if (getLastNonConfigurationInstance() != null) {
                task = (MyAsyncTask) getLastNonConfigurationInstance();
                if (task != null) {
                    if (!(task.getStatus().equals(AsyncTask.Status.FINISHED))) {
                        showProgressDialog();
                    }
                }
            }
        }

        @Override
        public Object onRetainNonConfigurationInstance() {
            if (pd != null)
                pd.dismiss();
            if (task != null)
                return (task);
            return super.onRetainNonConfigurationInstance();
        }


        private void showProgressDialog() {
            if (pd == null || !pd.isShowing()) {
                pd = new ProgressDialog(MainActivity.this);
                pd.setIndeterminate(true);
                pd.setTitle("DOING..");
                pd.show();
            }
        }

        private void dismissProgressDialog() {
            if (pd != null && pd.isShowing())
                pd.dismiss();
        }

        public class MyAsyncTask extends AsyncTask<String, Void, Boolean> {
            @Override
            protected void onPreExecute() {
                showProgressDialog();
            }

            @Override
            protected Boolean doInBackground(String... args) {
                try {
                    Thread.sleep(5000);
                    data = "result from ws";
                } catch (Exception e) {
                    return true;
                }
                return true;
            }

            protected void onPostExecute(Boolean result) {
                if (result) {
                    dismissProgressDialog();
                    updateUI();
                }
            }
        }

        private void updateUI() {
            tv.setText(data == null ? "null" : data);
        }

        public void startClicked(View target) {
            task = new MyAsyncTask();
            task.execute("start");
        }
    }

Answer 1

What I have done is as follows:

1- Add android:freezesText="true" to all my TextViews. This enables TextViews to save their states on configuration changes.

2- Make your AsyncTask a static inner class.

3- Modify AsyncTask to keep a reference to the Activity it lives in. So AsyncTask can access UI widgets of Activity via this reference.

4- Here, it is important to keep a valid activity reference during screen rotations. So, override onDestroy method and unbind the Activity from AsyncTask. Thus, task wont keep the old(died) activity.

5- In onRetainNonConfigurationInstance, if task is still running, update its activity reference with the current activity, so it is successfully tied to new activity.

6- Finally, in onPostExecuteMethod, access the UI elements of the Activity via activity reference.

Complete Working Solution:

layout\activity_main.xml :

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" 
    android:orientation="vertical">

    <Button 
        android:text="Start"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="startClicked"
        />
    <TextView
        android:freezesText="true"
        android:id="@+id/hello"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world"
        tools:context=".MainActivity" />
</LinearLayout>

layout-land\activity_main.xml:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" 
    android:orientation="horizontal">

    <Button 
        android:text="Start"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="startClicked"
        />
    <TextView
        android:freezesText="true"
        android:textSize="36dp"
        android:textColor="#ff0000"
        android:id="@+id/hello"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world"
        tools:context=".MainActivity" />
</LinearLayout>

MainActivity.java:

package com.example.asynctaskconfig;

import android.app.Activity;
import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

public class MainActivity extends Activity {
    static ProgressDialog pd;
    MyAsyncTask task;
    TextView tv;

    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        setContentView(R.layout.activity_main);

        tv = (TextView) findViewById(R.id.hello);

        if (getLastNonConfigurationInstance() != null) {
            task = (MyAsyncTask) getLastNonConfigurationInstance();
            if (task != null) {
                task.activity = this;
                if (!(task.getStatus().equals(AsyncTask.Status.FINISHED))) {
                    showProgressDialog();
                }
            }
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (task != null) {
            task.activity = null;
        }
    }

    @Override
    public Object onRetainNonConfigurationInstance() {
        if (pd != null)
            pd.dismiss();
        if (task != null)
            return (task);
        return super.onRetainNonConfigurationInstance();
    }

    private void showProgressDialog() {
        if (pd == null || !pd.isShowing()) {
            pd = new ProgressDialog(MainActivity.this);
            pd.setIndeterminate(true);
            pd.setTitle("DOING..");
            pd.show();
        }
    }

    private void dismissProgressDialog() {
        if (pd != null && pd.isShowing())
            pd.dismiss();
    }

    static class MyAsyncTask extends AsyncTask<String, Void, String> {
        MainActivity activity;

        public MyAsyncTask(MainActivity activity) {
            this.activity = activity;
        }

        @Override
        protected void onPreExecute() {
            activity.showProgressDialog();
        }
        @Override
        protected String doInBackground(String... args) {
            try {
                Thread.sleep(8000);
                return "data from ws";
            } catch (Exception e) {
                return "exception";
            }
        }

        protected void onPostExecute(String result) {
            activity.dismissProgressDialog();
            activity.tv.setText(result == null ? "null" : result);
        }
    }

    public void startClicked(View target) {
        task = new MyAsyncTask(this);
        task.execute("start");
    }
}