How to set an imageView's image from a string?

I have a list of entries and some bitmap files in the res/drawable-mdpi directory. I'm trying to load the image corresponding to the string value selected from the list by generating a path string and using bitmap factory. The problem is I don't think my path is right because the bitmap is always null, even for the default image.

String name = entries.get(position);
            String img = "res/drawable/logo_" + name.toLowerCase() + ".png"; // create the file name
            icon.setScaleType(ImageView.ScaleType.CENTER_CROP);

            // check to see if the file exists
            File file = new File(img);
            if (file.exists()){

                bm = BitmapFactory.decodeFile(img);
            }
            else{// use the default icon
                bm = BitmapFactory.decodeFile("logo_default.png");
            }

            // set the image and text
            icon.setImageBitmap(bm);

Does the res directory even get copied onto the device? What is the correct path I should be using, or should I be going about this differently?

Thanks