How to update UI thread when Network call is placed before rotating?

Question

Okay this is driving me nuts. I have a worker thread, (Network call) that needs to run separate of the UI thread, (Its actually a ThreadPoolExecutor but I simplified it to prove my point). If you run this code in portrait, without rotation, the text updates. I put in the delay there to allow for rotations to show my issue. If you start in portrait and before text updates rotation to landscape the text does not update. If you comment the code you can see the listener fire but the text never updates.

I am trying to simulate a custom network call running in a separate thread that may take some time to come back if the user rotates in between then the data gets lost. We are trying to prevent multiple network calls to save data usage on a phone.

package com.example.test;

import android.os.Bundle;
import android.os.Handler;
import android.app.Activity;
import android.content.res.Configuration;
import android.view.Menu;
import android.widget.TextView;
public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    int orientation = getResources().getConfiguration().orientation; 
    if (Configuration.ORIENTATION_LANDSCAPE == orientation) { 
        //Do SomeThing; // Landscape
    } else { 
        startBackgroundWork();
        //Do SomeThing;  // Portrait
    } 

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

private Handler mHandler = new Handler();

public void startBackgroundWork() {
    new WorkingThread(new SomeListener() {
        public void onSomethingDone(final Object result) {

            mHandler.post(new Runnable() {
                public void run() { 
                    ((TextView)findViewById(R.id.text)).setText((String)result);
                    //showMyDialog(result); 
                }
            });

        }    
    }).start();
}

public interface SomeListener {
    public void onSomethingDone(Object result);
}

public class WorkingThread extends Thread {
    private SomeListener mListener;

    public WorkingThread(SomeListener listener) {
        mListener = listener;
    }

    public void run() {
        /* do some work */
        try {
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        mListener.onSomethingDone("New Text");
    }
}
}

score 1 · Accepted Answer · edited May 23 '17 at 12:14

It's because on rotation, the activity is re created, therefore all your code is binded to the old activity. You should make a reference to your working thread :

private static WorkingThread mWorkingThread;
public void startBackgroundWork() {
    mWorkingThread = new WorkingThread(new SomeListener() {
        public void onSomethingDone(final Object result) {

            mHandler.post(new Runnable() {
                public void run() { 
                    ((TextView)findViewById(R.id.text)).setText((String)result);
                    //showMyDialog(result); 
                }
            });

        }    
    }).start();
}

then onCreate update it :

public class WorkingThread extends Thread {
    private SomeListener mListener;

    public WorkingThread(SomeListener listener) {
        mListener = listener;
    }

    public void run() {
        /* do some work */
        try {
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        mListener.onSomethingDone("New Text");
    }

    public void updateListener(SomeListener listener) {
        mListener = listener;
    }
}


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    startBackgroundWork();
}

public void startBackgroundWork() {
    if (mWorkingThread == null || mWorkingThread.isFinished()) { // Use a boolean to know if it still running


    mWorkingThread  = new WorkingThread(new SomeListener() {
        public void onSomethingDone(final Object result) {

            mHandler.post(new Runnable() {
                public void run() { 
                    ((TextView)findViewById(R.id.text)).setText((String)result);
                    //showMyDialog(result); 
                }
            });

        }    
    });
        mWorkingThread.start();

    } else { 
        mWorkingThread.updateListener(new SomeListener() {
        public void onSomethingDone(final Object result) {

            mHandler.post(new Runnable() {
                public void run() { 
                    ((TextView)findViewById(R.id.text)).setText((String)result);
                    //showMyDialog(result); 
                }
            });

        }    
    });
    } 
}

But there is some improvments you could make :

The WorkingThread class should be static to avoid direct reference to the old activity : Java: Static vs non static inner class
Then make a reference to the current activity, and update it when it is recreated
Make a method for update of the text, instead of having the code directly in the listener

This doesn't work because the startbackground is fired on every rotation if you put in the orientation code with your code changes then it does the same thing as before. Watch the thread fire and you'll see two worker threads running. — JPM, Aug 09 '13 at 14:32
I modified startBackgroundWork, if the thread is already running (on an orientation changed for example), then startBackgroundWork just update the listener (I reckon I probably should have created another method for that but you can do that later). It works because mWorkingThread is a static instance that is retain on rotation. (Anyway i think you figured it out because you accepted my answer) — NitroG42, Aug 09 '13 at 15:33

How to update UI thread when Network call is placed before rotating?

1 Answers1