how to change android wallpaper from outside of the activity class?

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Java

Mobile

Android

in the end I'm starting up a service that I will want to call to that class and change my phone's wallpaper.

in the mainActivity java file I can just write >

DisplayMetrics metrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(metrics);
int height = metrics.heightPixels;
int width = metrics.widthPixels;

Bitmap bmap2 = BitmapFactory.decodeResource(getResources(),   R.drawable.superman);
        Bitmap bitmap = Bitmap.createScaledBitmap(bmap2, width, height, true);

        WallpaperManager wallpaperManager =    WallpaperManager.getInstance(getApplicationContext());
        try {
            wallpaperManager.setBitmap(bitmap);
        } catch (IOException e) {
            e.printStackTrace();
        }

and this works great... it uploads the wallpaper and starches it to fit screen

but I can't use it in another java class.,

how do I do this on another java class, and then later on call it from my myService Class ?