我是否需要在类构造函数中设置初始值？

Question

I have the following class:

public class Detail
    {

        public Detail()
        {
            this.File = String.Empty;
            this.State = false;
            this.Tag1 = 0
        }

        public string File { get; set; }
        public bool   State { get; set; }
        public int Tag1 { get; set; }
    }
}

Do I need to set the initial values like this in the constructor or will these just default when I create the class. How about programming practice. Does it look better to set them here even if not needed?

Answer 1

State and Tag1 will default to false and 0 respectively, but File will default to null . If you want string.Empty , you'll have to assign it.

Answer 2

Member fields are initialized with default values for you. So, no you don't have to set if the value is default ( 0 for int , false for bool , null for reference types). However string.Empty is not default value for string . So you need to set it to string.Empty if null doesn't work for you.

The initial value of a field, whether it be a static field or an instance field, is the default value of the field's type.

The default value of a variable depends on the type of the variable and is determined as follows:

• For a variable of a value-type, the default value is the same as the value computed by the value-type's default constructor
• For a variable of a reference-type, the default value is null

Answer 3

No, you do not need to do this. All property values are automatically set to their default value when a class constructor is called. See this page for info on default values in C#.

You might want to consider it if you would rather have a string be empty rather than null, or whether or if you want a collection (a List for example) to be initialized automatically, though. What you've done certainly isn't bad practice at all, just unnecessary.

Answer 4

Clearly, in your example you can't set them in the properties themselves, because you don't have an explicit backing variable.

When you set default values in the constructor, it's fine, but you need to be careful to always call that constructor from others you may have, like:

public Foo () {
  this.Happy = true;
  this.BasicUnit = 92;
}

public Foo (bool happy) : this() {
   this.Happy = happy;
}

It can get a little confusing as to what is what. So, personally, I like to set default values explicitly in the backing variables.

-- Edit: I see I may have misinterpreted your question - as others have said, all member variables are given default values, local variables are not.