Dynamic Object Reference

[Guest]

I have a menu form that has a number of buttons that each launch a different
form. The syntax is the same except for the form name is different. How do
create a common function that launches a new form that excepts the form name
as an argument?

My current syntax:

Private Sub btnNewSearch_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnNewSearch.Click
Dim applicantion As New applicantion
applicantion.MdiParent = Me.MdiParent
applicantion.Show()
End Sub

Private Sub btnDispute_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnDispute.Click
Dim dispute As New dispute
dispute.MdiParent = Me.MdiParent
dispute.Show()
End Sub

Private Sub btnClientAdd_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnClientAdd.Click
Dim clientAdd As New clientAdd
clientAdd.MdiParent = Me.MdiParent
clientAdd.Show()
End Sub

I would like to create a VB function that works like this:

Private Sub launchForm(ByVal formName as string)
Dim form As New formName
form .MdiParent = Me.MdiParent
form .Show()
Sub

But the syntax wouldn't work because formName is not provided until Runtime.

Any thoughts? Thanks.

 

[Jon Skeet [C# MVP]]

I have a menu form that has a number of buttons that each launch a different
form. The syntax is the same except for the form name is different. How do
create a common function that launches a new form that excepts the form name
as an argument?

Use the sender parameter. That should let you find out which button has
been click, and you can have a map from button to which form should be
opened. If you really need to instantiate the forms dynamically though,
you'll need to use something like Activator.CreateInstance.

 

[Guest]

I assume I need to instantiate the form, that way the application can support
multiple instances of the forms with the application. Do you have a sample VB
code that performs this action? Thanks.

 

[Jon Skeet [C# MVP]]

I assume I need to instantiate the form, that way the application can support
multiple instances of the forms with the application. Do you have a sample VB
code that performs this action? Thanks.

As I said, Activator.CreateInstance is the way to go. Just call
Activator.CreateInstance(typeOfFormToConstruct) and it'll return you
one. You'll need to cast it (eg to Form) but that shouldn't be hard.

 

[Guest]

Jon, your solution doesn't appear to work with Option Strict on.

Does anyone else have a VB sample that is close to what I'm trying to
accomplish? Again, I'm trying to create a common function that will except
the name of the form to instatiate and launch. Otherwise I need to repeat the
same code for every button that launches a form. Thanks.

Josh.

 

[Jon Skeet [C# MVP]]

Jon, your solution doesn't appear to work with Option Strict on.

It should do, so long as you cast appropriately.

Could you post a short but complete program which demonstrates the
problem?

See http://www.pobox.com/~skeet/csharp/complete.html for details of
what I mean by that.

Does anyone else have a VB sample that is close to what I'm trying to
accomplish? Again, I'm trying to create a common function that will except
the name of the form to instatiate and launch. Otherwise I need to repeat the
same code for every button that launches a form. Thanks.

You definitely don't need to repeat the code, and you should (IMO) use
a dictionary from sender to the type of form you want to create, and
then Activator.CreateInstance to instantiate the type.

 

[Guest]

I was able to find a code sample online, here is the code:
Sub ShowForm(ByVal T As Type)
Dim F As New Form
F = CType(Activator.CreateInstance(T), Form)
F.MdiParent = Me.MdiParent
F.Show()
End Sub

It is modified from, URL:
http://www.vbcity.com/forums/faq.asp?fid=15&cat=Windows+Forms&

An example of the call:
Private Sub btnNewSearch_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnNewSearch.Click
ShowForm(GetType(applicantion))
End Sub

Josh.

 

[Guest]

If you are not able to provide VB code, can you at least provide pseudo code
to illustrate? If not, is there another MVP or MS member that can? Thanks.

Josh.

 

[Jon Skeet [C# MVP]]

If you are not able to provide VB code, can you at least provide pseudo code
to illustrate? If not, is there another MVP or MS member that can? Thanks.

I can after a while, but it would be easier if you'd post what you've
already got. That's a much more effective form of learning, too.

 

[Jon Skeet [C# MVP]]

I was able to find a code sample online, here is the code:
Sub ShowForm(ByVal T As Type)
Dim F As New Form
F = CType(Activator.CreateInstance(T), Form)
F.MdiParent = Me.MdiParent
F.Show()
End Sub

It is modified from, URL:
http://www.vbcity.com/forums/faq.asp?fid=15&cat=Windows+Forms&

An example of the call:
Private Sub btnNewSearch_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnNewSearch.Click
ShowForm(GetType(applicantion))
End Sub

Right. That all looks okay, except there's no reason to create a new
form at the start of the method and then throw it away again.

As I said, it's just a matter of casting (the CType).

 

[Guest]

Can you alter my code so that it still sets the MdiParent without creating a
new Form?

I've updated my code and put in a BLL class, here it is:

Public Shared Sub ShowFormAsMdiChild(ByVal newFormType As Type, ByVal
mdiParentType As Type)
Dim F As New Form

F = CType(Activator.CreateInstance(newFormType), Form)
F.MdiParent = CType(Activator.CreateInstance(mdiParentType),
Form).ActiveForm
F.Show()
End Sub

A sample call is:
util.ShowFormAsMdiChild(GetType(mainMenu), Me.GetType)

BTW, util is the name of the BLL Class.

Josh.

 

[Jeffrey Tan[MSFT]]

Hi Josh,

Thanks for your post.

I am not sure why you modified your original code like this, however, I
think this should meet your need:
Sub ShowForm(ByVal T As Type)
Dim F As Form 'get rid of the new keyword, so we only has a F
reference of type Form.
F = CType(Activator.CreateInstance(T), Form) 'this will
dynamically create an instance of child form type
F.MdiParent = Me.MdiParent 'set the dynamically created form as
our main form's MDI child.
F.Show()
End Sub

If I misunderstand your request, please feel free to tell me.
==================================================
Thank you for your patience and cooperation. If you have any questions or
concerns, please feel free to post it in the group. I am standing by to be
of assistance.

Best regards,
Jeffrey Tan
Microsoft Online Partner Support
Get Secure! - www.microsoft.com/security
This posting is provided "as is" with no warranties and confers no rights.

 

[Jon Skeet [C# MVP]]

Can you alter my code so that it still sets the MdiParent without creating a
new Form?

You still need to create a new instance of the appropriate form, but
you don't need to create a new bare System.Windows.Forms.Form as you
currently do with the line:

Dim F As New Form

Just use

Dim F As Form

instead.

 

[Jeffrey Tan[MSFT]]

Hi Josh,

Does our reply make sense to you? Is you still have any concern, please
feel free to feedback, thanks

Best regards,
Jeffrey Tan
Microsoft Online Partner Support
Get Secure! - www.microsoft.com/security
This posting is provided "as is" with no warranties and confers no rights.