如何对枚举进行空检查

Question

 public class myclass
    {
        public Details DetailsInfo { get; set; }
        public string name{ get; set; }
        public string Email { get; set; }
        public int subjects{ get; set; }
    }

public enum subjects{
maths,
english,
science,
}

Among these subjects is an enum. Even if I don't enter any value for subjects it takes 0 by default. This is the behavior of enum. Is there any way to check if I have chose any value for subject.

Note: I don't want to any value like undefined in the enum.

Answer 1

You could solve the issue in two ways.

First, define a None value (or whatever you want to name it) which represents 0 to indicate there is nothing chosen for an enum value:

public enum subjects{
    None = 0, //define this
    maths,
    english,
    science,
}

Alternatively, use Nullable<subjects> or subjects? in your class ( myclass ).

public class myclass
{
    public Details DetailsInfo { get; set; }
    public string name{ get; set; }
    public string Email { get; set; }
    public subjects? subj { get; set; } //note the question mark ?
}           

Of the two methods, the first one is more common. Thus I would rather use the first one.

Answer 2

You can change the class to look like this:

 public class myclass
    {
        public Details DetailsInfo { get; set; }
        public string name{ get; set; }
        public string Email { get; set; }
        public subjects? subject { get; set; }
    }

So that the subject is nullable. It means that when you have not set it. It will be null