asked on

How to call a function when I only have the functionname as a string

This is a simplified version of my problem so please dont ask why I do
it this way!

I want to create an array of a user-defined structure. The structure
contains a control and a functionname. So something like below.

MyArray = {(control1, FunctionName1),
(control2, FunctionName2),
(control3, FunctionName3), ... }

Now I want to iterate through the array and call the related function
if the control is enabled:

for each Structure in MyArray
if Structure.control.enabled then
Call Structure.FunctionName 'DOES NOT WORK
end if
next

But how do I call a function just specified by its name? Can I use Eval
or do I need to specify a reference to the function in the structure
instead of the functionname?

SOLUTION

Bob Learned

membership

This solution is only available to members.

To access this solution, you must be a member of Experts Exchange.

Start Free Trial

ASKER CERTIFIED SOLUTION

Mike Tomlinson

membership

This solution is only available to members.

To access this solution, you must be a member of Experts Exchange.

Start Free Trial

3895

ASKER

Both answer is exactly what I wanted! The CallByName function seems to be the most simple. Before I split the points between you, I would like to ask the following:

A problem by calling functions this way is that I can not check for misspelled functionnames at design-time, and thus can get runtime-errors. So instead of having the functionname in my structure, could I have something like a reference to the function (maybe AddressOf functionname)? This way I would avoid runtime errors! But how do I execute the function by reference?

Mike Tomlinson

If you are not sure if the function name is correct then how could you possibly get a correct reference? ;)

A function reference in .Net is called a Delegate by the way...

3895

ASKER

I know what my functionname is but if I type it in my structure as a string, there is a chance that I misspell. I will not discover the misspell until I get a runtime error telling me that the function does not exist. If I use a delegate the program will not compile when I try to reference a misspelled function. Isn't taht correct???

Mike Tomlinson

Bottom line is if you are using a STRING to store the name of the function then you will not know if it is mispelled until runtime. You will just have to catch the exception with a Try...Catch block.

3895

ASKER

I found a solution to call a function by reference. This way I catch misspelled functionnames at compile-time.

Public Class Form1
Inherits System.Windows.Forms.Form

Delegate Sub MethodDelegate()

Public Structure Test
public mControl As Control
Public mDelegate As MethodDelegate

Public Sub New(ByVal control As Control, ByVal methodDelagate As MethodDelegate)
mControl = control
mDelegate = methodDelagate
End Sub
End Structure

Private Sub Form3_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim lTest as new Test(textbox1, New myMethodDelegate(AddressOf function1)) 'function1 has to exist. Otherwise compile-error!
lTest.mDelegate.Invoke() 'This calls function1
End sub

Private Sub function1
msgbox "Function call"
End sub

End class