StrataFrame Forum » .NET Forums » General .NET Discussion » How to use reflection to open a form

How to use reflection to open a form

Greg McGuffey — Tue, 23 Jan 2007 10:59:34 GMT

My brain hurts a lot trying to figure this out. I would like to be able to have a property that defines the type of a form that I will open. I think I have that down:

Property ProjectSelectorType as System.Type
...
End Property

I can set the property with code like (UserContext is a static class, containing the ProjectSelectorType):

UserContext.ProjectSelectorType = GetType(myApp.ProjectSelectorForm)

So far so good. Now I need to open it. I tried this, which didn't work:

Dim frm As Object = Activator.CreateInstance(UserContext.ProjectSelectorType)
Dim mdiParentInfo As System.Reflection.PropertyInfo = UserContext.ProjectSelectorType.GetProperty("MdiParent")
mdiParentInfo.SetValue(frm, MicroFour.StrataFrame.Application.StrataFrameApplication.MainForm, Nothing)

' The next line throws an exception, my guess because Show() has two overloads
Dim showInfo As System.Reflection.MethodInfo = UserContext.ProjectSelectorType.GetMethod("Show")
showInfo.Invoke(frm)

As mentioned, it doesn't like the GetMethod("Show") call.

What am I doing wrong here? Is there a better way to do this?

I also tried interfaces, but I needed to pass an instance of the form implementing the interface. I don't want the form to be instantiated all the time, just when it's needed.

Thanks!

RE: How to use reflection to open a form

Trent L. Taylor — Tue, 23 Jan 2007 10:59:34 GMT

[quote]How do you handle constructor parameters? I.e. I would normally do this:[/quote]

The Activator.CreateInstance supports parameters. It accepts a ParamArray and will pass these to the constructor of the object being created. You can create an overload on the LaunchForm method that accepts parms as well:

    [codesnippet]Private Sub LaunchForm(ByVal FormType As System.Type, ByVal ParamArray Parms() As Object)
        Activator.CreateInstance(FormType, Parms)
    End Sub[/codesnippet]

RE: How to use reflection to open a form

Greg McGuffey — Tue, 23 Jan 2007 10:26:14 GMT

Thanks! It was the casting that I wasn't getting. Cast it to a form and then you have access to MDIParent and Show...got it :D

Now, the next question(s) (when haven't I had a next question ;) ):

- How do you handle constructor parameters? I.e. I would normally do this:

Dim frm As New MyForm(arg1, arg2)

- What about setting custom properties or calling custom methods? I normally try to keep an configuration to the constructor, but occassionally, that doesn't work (signatures are the same). I.e. how to handle:

Dim frm As New MyForm(arg1, arg2)
frm.MySpecialProperty = 8
frm.SetAnotherSpecialProperty("some text")

Thanks!

RE: How to use reflection to open a form

Trent L. Taylor — Tue, 23 Jan 2007 09:49:43 GMT

Generally we will create a method that looks something like this in the main MDI form:

[codesnippet]Private Sub LaunchForm(Byval FormType As System.Type)
'-- Establish Locals
Dim loForm As SYstem.Windows.Forms.Form

'-- Create the form
loForm = CType(Activator.CreateInstance(FormType), System.Windows.Forms.Form)

'-- Set the MDI
loForm.MDIParent = Me

'-- Show the Form
loForm.Show()
End Sub[/codesnippet]

Then to call or launch the form:

[codesnippet]LaunchForm(GetType(MyForm))[/codesnippet]