iOS10中UISearchController对searchBar的修改

当有需求要修改searchBar的背景颜色或者文本框颜色时，ios9的代码已不能修改。记录。

根据版本的不同做不同的处理：
1、在ios10一下，获得searchBarTextField是lastObject，ios10是第二个
2、修改searchBar的背景色，10以下是，直接修改searchBar的backgroundImage；10以上，直接获得searchBackground这个视图，然后设置alpha为0，在对searchController的背景进行修改。

  - (void)willPresentSearchController:(UISearchController *)searchController {
    UIView *searchBarTextField = nil;
    if ([[UIDevice currentDevice].systemVersion floatValue] > 10.0) {
        UIView *searchBackground = [[searchController.searchBar.subviews.firstObject subviews] objectAtIndex:0];
        searchBackground.alpha = 0;
        searchController.view.backgroundColor = [UIColor redColor];
        searchBarTextField = [[searchController.searchBar.subviews.firstObject subviews] objectAtIndex:1];
    } else {
        searchController.searchBar.backgroundImage = [UIImage imageWithColor: [UIColor whiteColor]];
        searchBarTextField = [[searchController.searchBar.subviews.firstObject subviews] lastObject];
    }
 searchBarTextField.backgroundColor = [UIColor redColor];
}

关于searchBar的使用：
http://blog.csdn.net/jacob_ios/article/details/51347595