设置 NavigationBar title 字体大小 颜色

// 属性参数在 NSAttributedString.h 文件中
//这里我们设置的是颜色，字体大小,还可以设置其他，具体可以参见api
UIColor * color = [UIColor whiteColor];
UIFont *font = [UIFont systemFontOfSize:19];

NSMutableDictionary *dict=[NSMutableDictionary dictionary];
[dict setObject:color forKey:NSForegroundColorAttributeName];
[dict setObject:font forKey:NSFontAttributeName];

UINavigationBar *bar = [UINavigationBar appearance];
bar.titleTextAttributes = dict;