How do I do operations on an inherited base constructor in C#?

Question

Example

public class ClassA
{
    public ClassA(string someString){}
}

public class ClassB : ClassA
{
    public ClassB(string someString):base(someString.ToLower()){}
}

I call the inherited ClassB constructor. I pass in a null. ToLower() throws an exception on a null. I want to check for a null before that happens. How can I do this?

Answer 1

Simple. Using null-coalescing operator :

public ClassB(string someString) : 
    base((someString ?? "").ToLower())
{
}

Or using ternary operator

public ClassB(string someString) : 
    base(someString == null ? "" : someString.ToLower())
{
}

Better yet, I'd suggest you to add a no-arg constuctor to ClassB , which will call base(string.Empty) .

Answer 2

尝试这个：

base(someString == null ? string.Empty : someString.ToLower())

Answer 3

Try this

public class ClassA
{
    public ClassA(string someString) { }
}

public class ClassB : ClassA
{
    public ClassB(string someString) : base(someString == null  ? "" :  someString.ToLower()) { }
}

Answer 4

You have already gotten answers on your question, but I just want to add that the approach strikes me as a bit odd. Is it really the caller's responsibility to make sure that the input is in lower case? I would definitely make this check and conversion in the base class constructor instead:

class Base
{
    private string _someString;
    public Base(string someString)
    {
        _someString = someString != null ? someString.ToLower() : null;
    }
}

class Derived : Base
{
    public Derived(string someString) : base(someString) { }
}

This way the base class is not dependent on how the derived class chooses to pass the argument.

Answer 5

You should check if someString is null in your base class and act accordingly, otherwise you can do something like this, but I think its very unreadable.

public class ClassB : ClassA
{
    public ClassB(string someString):base((String.IsNullOrEmpty(someString)) ? String.Empty : someString.ToLower()){}
}