VB.NET WinForms实现接口

Question

VB.NET

I want some WinForms to implement an interface, and be able to pass these to a procedure which can 'see' the implemented properties as well as the 'standard methods' of a Form. This is what I have so far...

Public Interface IMyInterface

    Property MyProperty As String

End Interface

Public Class MyForm

    Implements IMyInterface

    Private _MyProperty As String

    Public Property MyProperty() As String Implements IMyInterface.MyProperty
    Get
        Return _MyProperty
    End Get
    Set(ByVal value As String)
        _MyProperty = value
    End Set

End Property

End Class

then, elsewhere I have my method as follows...

Public Sub DoSomething(MyForm As IMyInterface)

    MyForm.MyProperty = "x"
    MyForm.ShowDialog()

End Sub

The obvious problem is that the compiler doesn't know what .ShowDialog is, and if I pass my form in as 'MyForm As Form' it doesn't know what 'MyProperty' is. I understand the reasons for this, but not how to solve this problem. Is a simple casting to Form the correct way to address this?

Many thanks.

Answer 1

You need to inherit System.Windows.Forms.Form to gain all regular form functionality and then Implement IMyInterface .

Public Class MyForm
    Inherits System.Windows.Forms.Form
    Implements IMyInterface

Passing MyForm As IMyInterface into the DoSomething() method is fine, however to use the regular form methods you'll need to cast it. Alternatively you could pass in the Form and then cast to IMyInterface , your choice.

Public Sub DoSomething(MyIForm As IMyInterface)
        MyIForm.MyProperty = "x"

        Dim MyForm As Form = TryCast(MyIForm, Form)
        MyForm.ShowDialog()

Answer 2

Another aproach can be using your own base class

Public Class MyBaseForm
    Inherits System.Windows.Forms.Form

    Public Property MyProperty As String

End Class

Then all your forms can inherit that base form

Public Class MyForm
    Inherits MyBaseForm

End Class

And you can use property and standard method of System.Windows.Forms.Form without casting

Public Sub DoSomething(someform As MyForm)
    someform.MyProperty = "Some value"
    someform.ShowDialog()
End Sub