CallByName - Calling Methods/Properties by their name

 2 Text boxes: Named txtValue1 and txtValue2

 1 Combo box: Named cmbAction

 1 Label: Named lblResult

 1 command button: Named cmdExecute

I've named the form "frmMain". This is standard for all my projects. it isn't really necassary for this project though.
The placement of the controls does not really matter.
Okay double click on the form so that you get the code window, and add the following:

Public Sub Form_Load()


 With cmbAction

     .AddItem "Multiply"

     .AddItem "Minus"

     .AddItem "DivideBy"

     .AddItem "Plus"

     .ListIndex = 0


  End With

End Sub

The items added to the combobox are the "mathematical actions" we're going to use in our sample application.
Listindex = 0 only sets the first item as an active item.

Now, we have to make our command button "cmdExecute" do something. So, add the following code:


Private SubcmdExecute_Click()

 lblResult.Caption = CallByName(frmMain, cmbAction.Text, VbMethod, txtValue1, txtValue2)

End Sub



This is the important part, especially for this tutorial. That's why I'm going to explain it very detailed.

The syntax of CallByName is as following:

Function CallByName(Object As Object, ProcName As String, CallType As VbCallType, Args() As Variant)

Object as Object: This is the object that contains the property/procedure you're calling by name.

So if you want to use the "Left" property of a command button, the object should be the command button.

If it's a procedure in a form, you need to put the form name here.

ProcName As String: When calling CallByName you have to specify the property/procedure you're going to call or modify, in this sub.
So if you want to call the "Left" property of a command button, you need to put "Left" here.

CallType as VbCallType: Specify's the type of thing you're calling. A Property(VbLet,VbGet,VbSet) or a procedure(VbMethod).
In this example we are going to use VbMethod, because we are going to call functions.

Args() As Variant: This is not a real array, like you might think. You just have to put all the values you want to use after each other (with "," as separator). They have to match the Method/Property you're calling!
In our example we are going to use functions which need to values. txtValue1 and txtValue2.
Now if you're going to change a property "Left" of a command button, you just specify one new value, which is going to be the new "Left" value.

I hope you all understand this. It looks complex the first time, but with some code, you're going to find this very easy!

We're now going to put our mathematical code into the program.
It's very simple math.

I'm not all too good in Math, but the main point is that you understand how to use CallByName

Add the following code:

Public Function Multiply(lngValue1 As Long, lngValue2 As Long) As Long

  Multiply = lngValue1 * lngValue2

End Function

Public Function Minus(lngValue1 As Long, lngValue2 As Long) As Long

  Minus = lngValue1 - lngValue2

End Function

Public Function DivideBy(lngValue1 As Long, lngValue2 As Long) As Long

  DivideBy = lngValue1 / lngValue2

End Function

Public Function Plus(lngValue1 As Long, lngValue2 As Long)As Long

  Plus = lngValue1 + lngValue2

End Function

Well, those functions should be self explaining. They require two values, and then they do the action represented by the Function's name.

Got everything ready? Okay run the program [F5].

Enter a number in both textboxes. Very high numbers will probably cause an "Overflow", so don't enter malicious numbers :o)

Now, when you press the command button the action you have chosen in the combo box will be executed!

Only by using the name of the Procedure, and the CallByName method.

Tutorial 2 - Properties

The sample application will change the caption of the form (Let), enable/disable a timer (Get/Let), and move a command button around the form.

In this tutorial, we need the following controls:

1 Form: Named FrmMain. ScaleMode = VbPixel (3)!

2 Command buttons: Named cmdChangeCaption and cmdEnableTimer

1 Timer: Named tmrMove. Interval = 100

Placement does not really matter.

We are going to change the Form's caption first. Add the following code to the command button named "cmdChangeCaption":

Private Sub cmdChangeCaption_Click()

  CallByName frmMain, "Caption", VbLet, "CallByName - Tutorial 2"

End Sub

So what does this code do? Well, when you click on the command button, it will change the caption of the form to "CallByName - Tutorial 2".
VbLet means that you set the property of an object.

Now where are going to add some code that might look complex, but in fact it really isn't.

Add the following code to cmdEnableTimer:

Private Sub cmdEnableTimer_Click()

  CallByName tmrMove, "Enabled", VbLet, Not CallByName(tmrMove, "Enabled", VbGet)

End Sub

This code sets the property "Enabled" of the timer. The code is made very efficient, because when you press again it will set the propery to the inverse of the current state.
True-False-True-False, and so on... It retrieves the property using CallByName using "VbGet".

At the moment, the timer does nothing. So let's change that. Add the following code to "tmrMove":

Private Sub tmrMove_Timer()

  CallByName cmdEnableTimer, "Left", VbLet, CInt(Rnd(frmMain.ScaleWidth)) * 100

  CallByName cmdEnableTimer, "Top", VbLet, CInt(Rnd(frmMain.ScaleHeight)) * 100

End Sub

This code will put the command button on random places (in your form), after you press "Enable Timer".

If you click again on the button. (Or press enter when it has the focus) the Timer will disable.
Pressing it again will enable it, and so forth...

I hope you enjoyed my first tutorial! If there are any comments please do not hesitate to write them down!