CODEWITHSUNDEEP
androidandroid-imageviewandroid-imageandroid-asynctask
M.A.Murali
M.A.Murali

Reputation: 10158

how to change background image periodically in android

in my app in android, i need change background image in image view on 10 seconds once. so that i call a Async Task within a run method. when I execute the app it crashes. It gives the Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare() Exception to me.

I know I have to use Thread, but I do not know how to do so properly. Please help me.

This is my code sample:

    public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
        .................
    new Thread() 
    {
        public void run() 
        {
            while(true){
            try 
            {
                Thread.sleep(5000);
            } 
            catch (InterruptedException e) 
            {
                e.printStackTrace();
            }
            count = count + 1;

            new ImageChange().execute();
          }
        }       
    }.start();  

} // OnCreate End


class ImageChange extends AsyncTask<Void, Void, Void> 
{       
    protected void onPreExecute() { 

    }   
    protected void onPostExecute(Void unused) {
        iv1.setImageBitmap(b1);
        iv2.setImageBitmap(b2);
    }
    protected Void doInBackground(Void... arg0) {

        switch(count){

            case 1:            


                b1 = BitmapFactory.decodeFile(f1.getAbsolutePath());
                b2 = BitmapFactory.decodeFile(f2.getAbsolutePath());    
            break;  
            case 2:


                b1 = BitmapFactory.decodeFile(f2.getAbsolutePath());
                b2 = BitmapFactory.decodeFile(f1.getAbsolutePath());

            break;      
            default :
                count = 0;      
                b1 = BitmapFactory.decodeFile(f1.getAbsolutePath());
                b2 = BitmapFactory.decodeFile(f2.getAbsolutePath());

            break;    
        }

     return null;
    }
}

Upvotes: 2

Views: 1735

Answers (3)

M.A.Murali
M.A.Murali

Reputation: 10158

i solved the problem by using Handler Thread.

Upvotes: 0

Vito Gentile
Vito Gentile

Reputation: 14426

Probably, the problem is that you must execute the ImageChange.doInBackground() method in the UI thread. Try to change your code like this:

class ImageChange extends AsyncTask<Void, Void, Void> {

    Activity act;

    public ImageChange(Activity act) {
        this.act = act;
    }

    protected void onPostExecute(Void unused) {
        iv1.setImageBitmap(b1);
        iv2.setImageBitmap(b2);
    }
    protected Void doInBackground(Void... arg0) {

        switch(count) {
            case 1:            
                helperMethod(f1.getAbsolutePath(), f2.getAbsolutePath());
            break;  
            case 2:
                helperMethod(f2.getAbsolutePath(), f1.getAbsolutePath());
            break;      
            default :
                count = 0;      
                helperMethod(f1.getAbsolutePath(), f2.getAbsolutePath());
            break;    
        }

        return null;
    }

    private void helperMethod(String a, String b) {
        act.runOnUIThread(new Runable() {
            public void run() {
                b1 = BitmapFactory.decodeFile(a);
                b2 = BitmapFactory.decodeFile(b);
            }
        });
    }
}

Note that you must pass an Activity to the ImageChange class constructor. It means that you have to call the asyncTask in this way:

new ImageChange(this).execute();

Also consider the possibility of using the class TimerTask

EDIT: Change the Activity part of your code with this:

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
        .................

    new ImageChange().execute();

} // OnCreate End

And add the while(true) to the ImageChange class:

    protected Void doInBackground(Void... arg0) {
        while(true) {

            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            count = count + 1;

            switch(count) {
                ...    
            }
        }
        return null;
    }

EDIT2: You can solve the problem about onPostExecute inserting the code that must be execute after each iteration inside the while loop:

    protected Void doInBackground(Void... arg0) {
        while(true) {

            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            count = count + 1;

            switch(count) {
                ...    
            }
            act.runOnUIThread(new Runnable() {
                public void run() {
                    iv1.setImageBitmap(b1);
                    iv2.setImageBitmap(b2);
                }
            });
        }
        return null;
    }

The code you insert inside the while loop must run in the UI thread; in fact, every onPostExecute method of the AsyncTask class runs on UI thread.

Upvotes: 0

hovanessyan
hovanessyan

Reputation: 31463

You're calling the AsyncTask from a worker Thread. This way it has no access to the UI thread. You probably should consider using a Handler.

Upvotes: 1

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