One of the key features of VBA is its ability to implement interfaces, which allows developers to create reusable code that can be easily applied to different objects within an application. The Implements statement in VBA plays a crucial role in this process and enables objects to inherit the properties and methods of an interface. In this blog post, we will explore the purpose, syntax, examples, important notes and remarks, and conclude with feedback and views on the VBA Implements statement.
VBA Implements Statement
Purpose
The main purpose of the Implements statement in VBA is to allow objects to inherit the properties and methods of an interface, as mentioned earlier. By implementing an interface, objects can be assigned to a variable that is declared as that interface’s type and use its properties and methods without needing to know the underlying class.
Syntax of Implements Statement in VBA
The syntax for the Implements statement is as follows:
Class ObjectName Implements InterfaceName
'Code for implementing interface goes here
End Class
Here, ObjectName refers to the name of the class or object which is implementing the interface, and InterfaceName refers to the name of the interface being implemented.
Examples on the VBA Implements Statement
Example 1: Implementing a Simple Interface in VBA
Suppose we have an interface named ‘ITextExport’ with a single method ‘ExportTo’. We can implement this interface in a class named ‘TextDocument’ as shown in the code below:
Option Explicit
'Interface for exporting text
Public Interface ITextExport
Sub ExportTo(path As String)
End Interface
'Class for text documents
Public Class TextDocument Implements ITextExport
Public Sub ExportTo(path As String)
'Code to export text document
End Sub
End Class
In the above example, the TextDocument class implements the ITextExport interface, and by doing so, it inherits the ExportTo method of the interface.
Example 2: Implementing Multiple Interfaces
An object in VBA can inherit properties and methods from multiple interfaces. In this example, we have a class named ‘ExcelDocument’ that implements both the ITextExport and IImageExport interfaces.
Option Explicit
'Interface for exporting text
Public Interface ITextExport
Sub ExportTo(path As String)
End Interface
'Interface for exporting images
Public Interface IImageExport
Sub ExportTo(path As String)
End Interface
'Class for Excel documents
Public Class ExcelDocument Implements ITextExport, IImageExport
Public Sub ExportTo(path As String)
'Code to export Excel document to text or image
End Sub
End Class
Notice how both interfaces have a method with the same name ‘ExportTo’, but we can still differentiate between them by accessing them through the respective interface.
Example 3: Using an Interface in a Function
One of the benefits of using the Implements statement is that it allows developers to create reusable code that can be easily applied to different objects. In this example, we have a function named ‘ExportDocument’ that takes in an object that implements the ITextExport interface and exports it to the specified path.
Option Explicit
'Interface for exporting text
Public Interface ITextExport
Sub ExportTo(path As String)
End Interface
'Class for text documents
Public Class TextDocument Implements ITextExport
Public Sub ExportTo(path As String)
'Code to export text document
End Sub
End Class
'Function to export document
Public Function ExportDocument(doc As ITextExport, path As String)
doc.ExportTo path
End Function
In this function, we can pass in any object that implements the ITextExport interface, such as the TextDocument class we created earlier, and the function will work without any errors.
Example 4: Implementing a Custom Interface
Apart from the pre-defined interfaces, VBA also allows developers to create custom interfaces according to their requirements. In this example, we have an interface named ‘ICalculator’ with a method ‘Add’ that takes in two numbers and returns their sum. We can then implement this interface in a class named ‘Calculator’, as shown below:
Option Explicit
'Custom interface for calculator
Public Interface ICalculator
Function Add(num1 As Double, num2 As Double) As Double
End Interface
'Class for implementing calculator interface
Public Class Calculator Implements ICalculator
Public Function Add(num1 As Double, num2 As Double) As Double
Add = num1 + num2
End Function
End Class
Here, the Calculator class can be used to perform addition without needing to specify the formula every time.
Example 5: Using Implements with UserForms
Apart from classes and objects, Implements can also be used with UserForms in VBA. In this example, we have a UserForm named ‘AddTaskForm’ with a button that adds a task to a list. We can implement the ‘IAddTask’ interface in the UserForm and call its method ‘AddTask’ in the code behind the button.
Option Explicit
'Interface for adding tasks
Public Interface IAddTask
Sub AddTask(task As String)
End Interface
'UserForm for adding tasks
Public Class AddTaskForm Implements IAddTask
Public Sub AddTask(task As String)
'Code to add task to list
End Sub
End Class
'Button click event in UserForm
Private Sub btnAdd_Click()
Dim form As IAddTask
Set form = New AddTaskForm
form.AddTask txtTask.Value
End Sub
The above code shows how we can use the Implements statement to create a more efficient and reusable UserForm.
Important Notes and Remarks on VBA Implements Statement
Here are some important notes and remarks to keep in mind when using the Implements statement in VBA:
- The Implements statement can only be used with classes, not with standard modules or UserForms modules.
- When an interface is implemented, all the methods and properties of the interface must be present in the class.
- An object can inherit from multiple interfaces, but it can only inherit from one class.
- When a method is implemented from an interface, optional parameters cannot be used in the implementing code.
- If the interface contains a property, it must be implemented as a procedure with a ‘Get’ and a ‘Let’ component.
Conclusion
In conclusion, the Implements statement in VBA plays a crucial role in creating reusable and efficient code by allowing objects to inherit the properties and methods of an interface. We have discussed its purpose, syntax, and provided examples to showcase its functionality.
We have also mentioned important notes and remarks that should be kept in mind while using this statement. By mastering the implementation of interfaces in VBA, developers can achieve greater flexibility and code reuse in their projects.
We hope this blog post has provided a comprehensive understanding of the VBA Implements statement and its applications. If you have any feedback or views on this topic, we would love to hear them. Let us know your thoughts in the comments section below.
