CODEWITHSUNDEEP
vb.netvisual-studio
mzurita
mzurita

Reputation: 690

Throw message exception in custom property

I am developing a custom library with custom controls. I need Visual Studio shows a Message in Design Mode when user inserts an invalid value in a custom property, as visual studio does when you try Color.Transparent for BorderColor in a Button.

A piece of code:

Public Class ButtonWithBrigthness 'It inherits from Button in .Designer.vb

  Private _brigthness As Integer

  Public Property Brightness() As Integer
     Get
        Return _brigthness
     End Get
     Set (value as Integer)
        If (value >= 0 And value <= 10) Then
           _brigthness = value
        Else
           'Throw Exception for an invalid value....
        End If
     End Set
  End Property

End Class

Upvotes: 0

Views: 409

Answers (1)

Martin Verjans
Martin Verjans

Reputation: 4806

To know if you are in Design Mode or not, you can use the DesignMode Property.

Next you need to know that if you raise an exception from a property setter in design-mode, the property grid will catch it and display a message box saying "Invalid Property Value", the user can click on "Details" to see the custom message you put in. If you want to do better you show a Message Box indicating why it's not working.

Anyway, if you want to raise an exception :

Public Property Brightness() As Integer
    Get
       Return _brigthness
    End Get
    Set (value as Integer)
       'I rewrote the condition, but you don't have to, just put the exception in the else...
       If value < 0 Or value > 10 Then
           'Here we throw the Exception only in design mode
           'So at runtime just nothing will happen...
           If Me.DesignMode Then
               Throw New ArgumentOutOfRangeException("Brightness must be between 0 and 10")
           End If
       Else
          _brigthness = value
       End If
    End Set
 End Property

And if you want to show a nice Message Box...

Public Property Brightness() As Integer
    Get
       Return _brigthness
    End Get
    Set (value as Integer)
       If value < 0 Or value > 10 Then
           'Here we show the MessageBox only in design mode
           'So at runtime just nothing will happen...
           If Me.DesignMode Then
               MessageBox.Show("Brightness must be between 0 and 10", "Invalid Brightness Value")
           End If
       Else
          _brigthness = value
       End If
    End Set
 End Property

Upvotes: 1

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