Can't load an image from within a thread in Android

Question

I'm trying to load a remote image from the server using the following code:

imageViewClient = (ImageView) findViewById(R.id.imageViewClient);
try 
{
    URL thumb_u = new URL(c.getImage());
    Drawable thumb_d = Drawable.createFromStream(thumb_u.openStream(), "src");
    imageViewClient.setImageDrawable(thumb_d);                      

}
catch (Exception e) 
{

}

The image is showing fine but when I put the code into a new thread, the image is not loaded.

The code is:

new Thread() 
{
    @Override
    public void run()
    {
            //** Set imageview url
            try {
                URL thumb_u = new URL(c.getImage());
                Drawable thumb_d = Drawable.createFromStream(
                    thumb_u.openStream(), "src");

                imageViewClient.setImageDrawable(thumb_d);                      

            }
            catch (Exception e) {

            }

    }
}.start();

The image does not load, why not?

score 3 · Answer 1 · edited May 23 '17 at 12:01

3

You can't change the UI within a thread in this way. You should use asyncTask or the method runOnUiThread to properly change the User interface. Or even better, handler like this post

edited May 23 '17 at 12:01

Community

1
1

answered Feb 01 '13 at 20:56

StarsSky

6,721
6
38
63

score 1 · Accepted Answer · answered Feb 01 '13 at 20:55

you will need to use Activity.runOnUiThread for changing from background thread as :

 @Override
  public void run() {
     //** Set imageview url
     try {
        URL thumb_u = new URL(c.getImage());
         Drawable thumb_d = Drawable.createFromStream(
                              thumb_u.openStream(), "src");                      

        Your_current_Activity.this.runOnUiThread(new Runnable() {
        public void run() {
         // Chnage imageView bg here
        imageViewClient.setImageDrawable(thumb_d); 
        }
    });
       }
     catch (Exception e) {

    }

score 0 · Answer 3 · answered Feb 01 '13 at 20:59

As an alternative to trying to deal with threading manually like this (where you'll run into problems like this where you can't update the UI from another thread), take a look at this article and consider using something like AsyncTask which already has some of this infrastructure in place and in fact has an example for your very use case:

public void onClick(View v) {
  new DownloadImageTask().execute("http://example.com/image.png");
}

private class DownloadImageTask extends AsyncTask {
     protected Bitmap doInBackground(String... urls) {
         return loadImageFromNetwork(urls[0]);
     }

     protected void onPostExecute(Bitmap result) {
         mImageView.setImageBitmap(result);
     }
 }

score 0 · Answer 4 · answered Feb 01 '13 at 23:03

Here is a simple AsyncTask to download and cache an image from the web:

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.InputStream;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Environment;
import android.util.Log;
import android.widget.ImageView;

/**
 * Downloads an image from a URL and saves it to disk, to be referenced if the
 * same URL is requested again
 */
public class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {

    private static final String LOG = DownloadImageTask.class.getSimpleName();

    ImageView mImageView;

    public static final String IMAGE_CACHE_DIRECTORY = YourApplication
            .getContext().getExternalFilesDir(Environment.DIRECTORY_PICTURES)
            .getAbsolutePath();

    public DownloadImageTask(ImageView bmImage) {
        this.mImageView = bmImage;

        // TODO set to default "loading" drawable
        mImageView.setImageBitmap(null);
    }

    @Override
    protected Bitmap doInBackground(String... urls) {

        String url = urls[0];

        Log.v(LOG, "url: " + url);

        String filename = url.substring(url.lastIndexOf("/") + 1, url.length());

        Log.v(LOG, "filename: " + filename);

        Bitmap bmp = getBitmapFromDisk(filename);

        if (bmp == null) {
            try {
                InputStream in = new java.net.URL(url).openStream();
                bmp = BitmapFactory.decodeStream(in);
                writeBitmapToDisk(filename, bmp);
            } catch (Exception e) {
                Log.e("Error", e.getMessage());
                e.printStackTrace();
            }
        }

        return bmp;
    }

    @Override
    protected void onPostExecute(Bitmap result) {
        mImageView.setImageBitmap(result);
    }

    public boolean writeBitmapToDisk(String imageid, Bitmap bmp) {
        boolean saved = false;

        File path = new File(IMAGE_CACHE_DIRECTORY);
        path.mkdirs();
        File imageFile = new File(path, imageid);
        FileOutputStream imageOS = null;
        try {
            imageOS = new FileOutputStream(imageFile);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        saved = bmp.compress(Bitmap.CompressFormat.JPEG, 95, imageOS);
        return saved;
    }

    public Bitmap getBitmapFromDisk(String imageid) {
        Bitmap bmp = BitmapFactory.decodeFile(IMAGE_CACHE_DIRECTORY + "/"
                + imageid);
        return bmp;
    }

}

Which is implemented like so:

new DownloadImageTask(mImageView).execute("https://www.google.com/images/srpr/logo3w.png");

Can't load an image from within a thread in Android

4 Answers4