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]){
      //
    }