设置 UISearchBar 输入字体颜色 和placeHold

原理是通过KVC来实现

//获取searchBar里面的TextField

UITextField*searchField = [_searchBar valueForKey:@"_searchField"];

//更改searchBar 中PlaceHolder 字体颜色

[searchField setValue:[UIColor blackColor] forKeyPath:@"_placeholderLabel.textColor"];

//更改searchBar输入文字颜色

searchField.textColor= [UIColor blackColor];