C#嵌套类/结构可见性

我希望能够访问Messenger实例的成员,如msgr.title.Forsuccesses.

但是,我不希望能够从Messenger类外部实例化Messenger.titles.

我也愿意制作Messenger.titles一个结构.

我猜我需要某种工厂模式或其他东西,但我真的不知道我该怎么做.

见下文：

class Program {
    static void Main(String[] args) {
        var m = new Messenger { title = { ForErrors = "An unexpected error occurred ..." } }; // this should be allowed
        var t = new Messenger.titles(); // this should NOT be allowed
    }
}

public class Messenger {
    // I've tried making this private/protected/internal...
    public class titles {
        public String Forsuccesses { get; set; }
        public String ForNotifications { get; set; }
        public String ForWarnings { get; set; }
        public String ForErrors { get; set; }

        // I've tried making this private/protected/internal as well...
        public titles() {}
    }

    public titles title { get; private set; }
    public Messenger() {
        title = new titles();
    }
}