The VBA CallByName function is a powerful tool that allows developers to invoke a class method or property by its name, rather than directly referencing it like one would with the typical dot notation. This gives the developer more flexibility and control over their code, as they can dynamically call methods and properties based on certain conditions or user inputs.
VBA CallByName Function – Purpose, Syntax and Arguments
The CallByName function is commonly used in VBA programming to dynamically call methods and properties within objects. This can be particularly useful when working with large or complex objects that have a large number of methods and properties, as it eliminates the need for repetitive coding and referencing. Additionally, it allows for a more flexible and adaptable approach to coding, as it allows for changes to be made without having to rewrite specific lines of code.
CallByName (Object, ProcName, CallType [,[Args()]])
- Object: This is the object that contains the method or property to be called.
- ProcName: This is the name of the method or property to be called.
- CallType: This is the type of call to be made, which can be one of the following:
- vbMethod – calls a method
- vbGet – retrieves the value of a property
- vbLet – sets the value of a property
- vbSet – assigns an object reference to a property
- Args(): This is an optional parameter that specifies the arguments to be passed to the method or property. If the procedure does not have any arguments, this parameter should be omitted. Otherwise, it should be an array that contains the arguments to be passed.
Let’s say we have a Class Module called “Employee” that contains a property called “Salary” and a method called “RaiseSalary”. Normally, we would access and manipulate these by using the dot notation, like so:
Dim emp As New Employee
emp.Salary = 50000
However, using the CallByName function, we can dynamically call these methods and properties. For example, let’s say we have a variable called “propertyToCall” that contains the name of the property we want to access. We can use the CallByName function to call this property, like so:
Dim emp As New Employee
Dim propertyToCall As String
propertyToCall = "Salary"
'will retrieve the value of the Salary property
CallByName emp, propertyToCall, vbGet
propertyToCall = "RaiseSalary"
'will call the RaiseSalary method with an argument of 10000
CallByName emp, propertyToCall, vbMethod, 10000
- The CallByName function can only be used to call methods and properties that are public. Private methods and properties cannot be accessed using this function.
- The property or method name must be represented as a string in order to be passed into the CallByName function.
- The CallType argument is necessary for the function to know whether to call a method or retrieve a property value. If this argument is not specified correctly, the function will not work correctly.
- If the specified method or property doesn’t exist within the object, a runtime error will occur.
- The CallByName function can be extremely useful when working with user forms, as it allows for the creation of dynamic interfaces and forms that can change based on user inputs.
- It is important to note that overuse of the CallByName function can make code difficult to read and maintain. It is generally recommended to use this function sparingly and only when necessary for more complex tasks.
- The CallByName function is not limited to just class modules – it can also be used for built-in objects such as Worksheets and Range objects in Excel.
In summary, the VBA CallByName function is a valuable tool for VBA developers that allows for dynamic calling of methods and properties within objects. It provides a more flexible approach to coding and can save time and effort by eliminating the need for repetitive code. By understanding its purpose, syntax, arguments, example, remarks, and important notes, developers can effectively use this function to enhance their VBA projects.
Understanding VBA CallByName Function with Examples
VBA, or Visual Basic for Applications, is a programming language that is used to create macros and automate tasks in Microsoft Office applications. One of the frequently used functions in VBA is the CallByName function, which allows you to call a procedure or function by its name at run time. This means that instead of calling a specific procedure or function, you can specify the name of the procedure or function in a variable and VBA will execute it at run time. This function is particularly useful when you need to dynamically call different procedures or functions based on certain conditions. In this blog post, we’ll explore the CallByName function in detail and provide some practical examples to help you understand its usage.
Calling a Sub Procedure using CallByName
Let’s say you have a sub procedure called “DisplayMessage” that displays a message on the screen. Here’s an example of how the sub procedure looks like:
MsgBox "Welcome to VBA!"
Now, instead of directly calling this sub procedure, you can use the CallByName function to call it at run time. Here’s how you would use the CallByName function for this example:
CallByName Application.VBE.ActiveVBProject.VBComponents("Module1"), "DisplayMessage", VbMethod
Let’s break down the above code:
- Application.VBE.ActiveVBProject.VBComponents(“Module1”) is used to specify the module where the sub procedure is located. In this case, the sub procedure is located in “Module1”.
- “DisplayMessage” is the name of the sub procedure that you want to call using the CallByName function.
- VbMethod represents the type of procedure being called. In this case, it is a subroutine or sub procedure.
So, in simple terms, the CallByName function takes three arguments – the object where the procedure is located, the name of the procedure, and the type of procedure. Once these three arguments are specified, the CallByName function will execute the specified procedure.
Calling a Function using CallByName
Just like calling a sub procedure, you can also use the CallByName function to call a function at run time. Let’s say you have a function called “CalculateSum” that takes two numbers as input and returns their sum. Here’s an example of how the function looks like:
Function CalculateSum(num1 As Integer, num2 As Integer) As Integer
CalculateSum = num1 + num2
To call this function using the CallByName function, you would use the following code:
result = CallByName Application.VBE.ActiveVBProject.VBComponents("Module2"), "CalculateSum", VbMethod, 5, 10
Here’s a breakdown of the above code:
- Application.VBE.ActiveVBProject.VBComponents(“Module2”) specifies the module where the function is located. In this case, the function is located in “Module2”.
- “CalculateSum” is the name of the function that you want to call.
- VbMethod represents the type of procedure being called. In this case, it is a function.
- The last two arguments, 5 and 10, represent the values that will be passed to the function as its input parameters.
As a result, the CallByName function will return the value 15, which is the sum of 5 and 10, which were passed as input parameters to the CalculateSum function.
Calling a Dynamic Procedure using CallByName
One of the main advantages of the CallByName function is that it allows you to dynamically call different procedures or functions based on certain conditions. Let’s take a look at an example of how you can achieve this using the CallByName function.
Assume that you have two sub procedures, “SendEmail” and “SendText”, that are used to send emails and text messages respectively. Depending on the user’s input, you want to call the appropriate procedure to send the message. Here’s how you would achieve this using the CallByName function:
Dim option As String
option = InputBox("Do you want to send an email or a text message?")
If option = "email" Then
CallByName Application.VBE.ActiveVBProject.VBComponents("Module3"), "SendEmail", VbMethod, "firstname.lastname@example.org", "email@example.com", "Hello!"
ElseIf option = "text" Then
CallByName Application.VBE.ActiveVBProject.VBComponents("Module3"), "SendText", VbMethod, "firstname.lastname@example.org", "555-555-5555", "Hello!"
In this example, the user is prompted to enter their desired option – email or text – and based on their input, the appropriate procedure is called using the CallByName function. Notice how we are passing the necessary input parameters to the procedures as well.
Explanation of the CallByName Function
Now that we have seen some practical examples of how the CallByName function can be used, let’s dive a little deeper and understand how this function works.
The syntax for the CallByName function is as follows:
CallByName(Object, ProcedureName, CallType, [Args() As Variant])
- Object is the object where the procedure or function is located. This can be a form, module, workbook, worksheet, etc.
- ProcedureName is the name of the procedure or function that you want to call.
- CallType represents the type of procedure being called. This can be VbMethod, VbGet, or VbSet.
- Args (optional) represents the arguments to be passed to the procedure or function. This is an array of variant values.
Additionally, the CallByName function can also be used to retrieve or set the value of a property. In this case, the first argument of the function becomes the object whose property needs to be retrieved or set.
To summarize, the CallByName function is a powerful tool in VBA that allows you to dynamically call procedures and functions. This function can help in making your code more flexible and efficient by eliminating the need for hard-coded procedure calls. Keep in mind that the arguments for the CallByName function must be provided in the same order as the parameters of the procedure or function. With practice, you can use the CallByName function to significantly enhance the functionality of your VBA macros.