Variable holding a command

Question

Can I store a command (like messagebox.show) in a variable?

Answer 1

The short answer is NO.

 

Answer 2

The medium answer is sort of:

Code Snippet

  Private Sub Button1_Click(ByVal sender As System.Object, _

ByVal e As System.EventArgs) Handles Button1.Click

    CallByName(Me, "ShowMessagebox", CallType.Method)

  End Sub

  Public Sub ShowMessagebox()

    MessageBox.Show("Showing")

  End Sub

 

Edit:

I left out the variable.

 

Code Snippet

  Private Variable As String = "ShowMessageBox"

  Private Sub Button1_Click(ByVal sender As System.Object, _

ByVal e As System.EventArgs) Handles Button1.Click

    CallByName(Me, Variable, CallType.Method)

  End Sub

  Public Sub ShowMessageBox()

    MessageBox.Show("Showing")

  End Sub

 

Answer 3

Use a delegate.  For example:

Public Class Form1
  Private Delegate Function ShowMessageDelegate(ByVal msg As String) As DialogResult
  Private mShower As ShowMessageDelegate

  Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    mShower = AddressOf MessageBox.Show
  End Sub

  Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    mShower("howdy")
  End Sub
End Class

Answer 4

 

Hi JohnWein & nobugz,

 

I've heard it is possible to create a command Alias too.

 

Can one of you give an example as the OP may find that idea useful too.

 

 

Regards,

 

S_DS

 

Answer 5

Could you use the System.CodeDom om namespace?

Answer 6

NateNate,

 

If you don't mind me asking, why would one want to hold a messagebox command in a variable?

 

 

Answer 7

That was just an example.

Answer 8

I think the short answer was probably the realistic answer to your question.

 

VB.NET is a a compiled language and not an interpreted scripting language.  In the further examples using delegates or callbyName suggested by John Weir and Nobugz the will indeed work but are really allowing you to call a method and adjust things a little programmatically but these are limited and are not really holding a program statement in a variable and executing it.    So they may work with simple method calls but if your expecting to be able to store VB statements in variables and then execute them this isnt going to work.

 

So you cant store something like "Dim x as new foo" in a a variable and then "x.bar = 1" in another and execute them one after the other.

 

So I guess the medium answer may work for you but the short answer is probably the realistic one for being able to stored VB statements in variables and execute them at runtime.