currentBackgroundImage：获取按钮背景图片

nsdata *imagedata1=uiimagepngrepresentation(btn.currentbackgroundimage);//按钮背景图片转nsdata
    nsdata *imagedata2=uiimagepngrepresentation([uiimage imagenamed:@"资讯默认"]);//未选图片转nsdata
    if([imagedata1 isequaltodata:imagedata2]){
      //
    }