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Inheritance and initialization issue
f#

Hi,

I would like to create a simple type ColorButton which is basically just a button with a pre-attached event.

However, adding the event in the constructor seems a little akward. The following solution works :

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type ColorButton =
  inherit Button
    
  new() as x =
    let c = new ColorDialog()
    { inherit Button(Width = 75, BackColor=Color.Black)  }
    then    
      x.Click.Add(fun _ ->
        if c.ShowDialog() = DialogResult.OK then
          x.BackColor <- c.Color
      )

But I would have preferred using an implicit constructor. I have tried teh following two pieces of code, which both fail. Is there an alternative ?

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//Will not compile because base cannot be used to add events
type ColorButton() =
  inherit Button(Width = 75, BackColor=Color.Black)
  
  let c = new ColorDialog()
  
  let _ =
    base.Click.Add(fun _ ->
      if c.ShowDialog() = DialogResult.OK then
        b.BackColor <- c.Color
    )

//Will not work at runtime because, I presume, this does not know yet it inherits a button when it is defined (??)
type ColorButton() as this =
  inherit Button(Width = 75, BackColor=Color.Black)
  
  let c = new ColorDialog()
  
  let _ =
    base.Click.Add(fun _ ->
      if c.ShowDialog() = DialogResult.OK then
        b.BackColor <- c.Color
    )

Thank you

.

I don't know for sure, but try changing 'let _ = ...' to 'do ...'.

Roughly, the model is

inside the 'let's that comprise the implicit/primary constructor body, you init local variables and don't reference 'this' yet

inside the 'do's that comprise the implicit/primary constructor body, at this point the object is fully constructed and you can refer to 'this'

By on 3/20/2009 4:51 AM ()

Thanks a lot

By on 3/23/2009 2:09 AM ()

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