Question

say I have two constructors for a windows form

Sub New (byref Foo as Foo)
    InitializeComponent()
    ...do some work
End Sub

and

Sub New (byref Foo as Foo, Bar as Bar)
    InitializeComponent()
    _bar = Bar
    Me.New(Foo)
End Sub

When using the second constructor, InitializeComponent is called twice. Is that OK? Should I try and prevent it? How?

You might say I could eliminate it from the second constructor, but is it OK for me to start making assignments (like _bar = Bar) before calling InitializeComponent?
Are there any guidelines on what you should or shouldn’t do before calling InitializeComponent? Or is it just safe to call it twice without any real consequences?

Cheers!

Answer 1

Call InitializeComponent only in deepest constructor (with biggest number of parameters). And then chain other constructors to call this constructor and provide default values for missing parameters.

Here is C# example

public MyForm(Foo foo)
  : this(foo, null)
{   
}

public MyForm(Foo foo, Bar bar)
{
   InitializeComponent();
   _bar = bar;
   // do some work
}

I believe in VB it will look like this

Public Sub New(foo As Foo)
    Me.New(foo, Nothing)
End Sub

Public Sub New(foo As Foo, bar As Bar)
    InitializeComponent()           
    _bar = bar
    ' do some work
End Sub