在派生类的基类中设置默认属性

Question

Ok so, I've run into an interested and probably simple problem. I have a base class that is inherited by another class (child). I have the same parameterless constructor in the base and the child. I would like to set defaults in the child that propagate into the base properties. I would like to do something like this:

public partial class baseclass
{
    public baseclass() {
        //never called if instantiated from baseclass(string newp1)
        p1 = "";
        p2 = "google";
    }

    public baseclass(string newp1) {
        p1 = newp1; //p2 will be "" and p1 will be newP1
    }

    public string p1 { get; set; }
    public string p2 { get; set; }
}

public partial class childclass : baseclass
{
    public childclass() { 
        //How can I call this to set some default values for the child?
        p2 = "facebook";
    }

    public childclass(string newp1) : base(newp1) {
        p1 = newp1; //p2 needs to be "facebook"
    }

}

Answer 1

Use constructors chaining if you have duplicated code in several constructors:

public class baseclass
{
    public baseclass() : this("google") { }
    public baseclass(string newp1)
    {
       p1 = newp1; // the only place in your code where you init properties
       p2 = "";
    }

    public string p1 { get; set; }
    public string p2 { get; set; }
}

Child class should inherit baseClass

public class childclass : baseclass
{
    public childclass() : this("facebook") { } // you can also call base here
    public childclass(string newp1) : base(newp1) { }
}

Also keep in mind that parital just allows you split class/method definiton in several parts (eg keep it in different files). It is useful when you are generating classes (eg from database tables) but still want to add/customize something in generated classes. If you will put customized code directly into generated files, then it will be lost after classes re-generation. Read more

Answer 2

You can create a protected constructor in base class and call it in child class:

    public class Base
    {
       public Base(int value1, int value2) { ... }
       protected Base(string value1) { ... } // only for child class
    }

    public class Child : Base
    {
       public Child() : Base("Value") { ... }
    }