I think you should get the bitmap from imageview and use that bitmap to set wallpaper.Like this:--
ImageView imageView = (ImageView) findViewById(R.id.full_image_view);
imageView.setImageResource(imageAdapter.mThumbIds[position]);
Button buttonSetWallpaper = (Button)findViewById(R.id.setwallpaper);
buttonSetWallpaper.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
WallpaperManager myWallpaperManager
= WallpaperManager.getInstance(getApplicationContext());
try {
Bitmap bitmap=((BitmapDrawable)imageView.getDrawable()).getBitmap();
if(bitmap!=null)
myWallpaperManager.setBitmap(bitmap);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});