android - Updating TextView from Async Task which use custom program dialog

Question

In one of my app, I have a scenario where I need to do some background task. For doing that I am using Async Task. Also I am using custom progress dialog. Below is the layout of the custom progress dialog

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/layout_root"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_gravity="center_vertical|center_horizontal"
    android:orientation="vertical" >

    <ProgressBar
        android:layout_width="60dp"
        android:layout_height="60dp"
        android:indeterminateDrawable="@drawable/progressloader" 
        android:layout_gravity="center"/>

    <TextView
        android:id="@+id/progressMessage"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="@color/black"
        android:textSize="18sp"
        android:text="Please wait...." />

</LinearLayout>

Everything works fine but when I try to set text to TextView then I am getting java NullPointerException.

AsyncTask code

private class InitialSetup extends AsyncTask<String, Integer, Long> {

        ProgressDialog dialog = new ProgressDialog(getParent(),R.style.progressdialog);


        @Override
        protected void onPreExecute() {
            dialog.show();
            dialog.setContentView(R.layout.progressbar);

        }

        @Override
        protected Long doInBackground(String... urls) {
                    //    txtView.setText("Testing");    here I am getting the error
            fetchDetails();

            return 0;
        }

        @Override
        protected void onPostExecute(Long result) {

            if (this.dialog.isShowing()) {
                this.dialog.dismiss();
            }

            populateUI(getApplicationContext());
        }
    }

MainActivity

public class SummaryActivity extends Activity {


final TextView txtView = (TextView)findbyid(R.id.progressMessage);
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.accountsummary);

              new InitialSetup().execute("");

    }
}

Answer 1

If I understand correctly, your TextView of which you want to set the text can be found in the xml file progressbar.xml (i.e. R.layout.progressbar). This TextView can be obtained once the content view has been set (using setContentView()). In your code you set it before this call is been and the code of mussharapp, he is calling it to early. Namely, he calls it after the setContentView(R.layout.accountsummary) call which does not contain the TextView. Consequently, the variable txtView will be NULL and you will get a NullPointerException.

What you should do is the following:

• Set the variable txtView in onPreExecute, after setContentView is called.
• Based on Paresh Mayani's explanation: Use the runOnUiThread method.

For the code look down below:

private class InitialSetup extends AsyncTask<String, Integer, Long> {

        ProgressDialog dialog = new ProgressDialog(getParent(),R.style.progressdialog);
        // The variable is moved here, we only need it here while displaying the
        // progress dialog.
        TextView txtView;

        @Override
        protected void onPreExecute() {
            dialog.show();
            dialog.setContentView(R.layout.progressbar);
            // Set the variable txtView here, after setContentView on the dialog
            // has been called! use dialog.findViewById().
            txtView = dialog.findViewById(R.id.progressMessage); 
        }

        @Override
        protected Long doInBackground(String... urls) {
            // Already suggested by Paresh Mayani:
            // Use the runOnUiThread method.
            // See his explanation.
            runOnUiThread(new Runnable() {
               @Override
               public void run() {
                  txtView.setText("Testing");       
               }
            });

            fetchDetails();
            return 0;
        }

        @Override
        protected void onPostExecute(Long result) {

            if (this.dialog.isShowing()) {
                this.dialog.dismiss();
            }

            populateUI(getApplicationContext());
        }
    }