Glide assert: java.lang.IllegalArgumentException: You must call this method on the main thread

Update image in main ui thread

runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            Glide.with(MainActivity.this)
                                    .load("image URL")
                                    .into(imageView);
                        }
                    });

The into(ImageView) method of Glide requires you to call it only on main thread, but when you pass the loading to a Timer it will be executed in a background thread.

What you can do is to retrieve a bitmap by calling get() instead of into() and then set that bitmap on the ImageView by calling setImageBitmap().

Glide.with(getApplicationContext())
     .load("your url")
     .asBitmap()
     .into(new BitmapImageViewTarget(imgView) {
      @Override
      protected void setResource(Bitmap resource) {
       //Play with bitmap
        super.setResource(resource);
      }
    });

You can also take a look at this document for more information.

Posting the code just in case it helps someone.

Bitmap myBitmap = Glide.with(applicationContext)
        .load(yourUrl)
        .asBitmap()
        .centerCrop()
        .into(Target.SIZE_ORIGINAL,Target.SIZE_ORIGINAL)
        .get()
imageView.setImageBitmap(myBitmap);