When and why should I use ClassName : this(null)?

Question

i can't understand the difference between a simple bare

Public ClassName() {}

and

Public ClassName() : this(null) {}

I know I can use it only if i have a +1 overloaded ctor, but I can't understand the advantages of defining the parameterless constructor this way.

Answer 1

This permits the single-param constructor to have all the logic, so it isn't repeated.

public ClassName() : this(null) {}

public ClassName(string s)
{
    // logic (code)
    if (s != null) {
        // more logic
    }
    // Even more logic
}

I hope it's clear that the "logic" and "even more logic" would have needed to be repeated in the parameterless constructor if not for the this(null).

Answer 2

One very useful case is situations like WinForms where the designer requires a prameterless constructor but you want your form to require a constructor.

public partial SomeForm : Form
{
    private SomeForm() : this(null)
    {
    }

    public SomeForm(SomeClass initData)
    {
        InitializeComponent();

        //Do some work here that does not rely on initData.           

        if(initData != null)
        {
           //do somtehing with initData, this section would be skipped over by the winforms designer.
        } 
    }
}