In visual basic, the Partial method is a special type of method and it will contain a declaration part in one partial class and the definition part in another partial class or in the same partial class.
Generally, the partial methods will exist either in partial class or structure and it will contain two main parts one is declaration and definition. Here, the declaration part represents the signature of the partial method and the definition part will represent the implementation of a partial method.
In partial method, the definition part is optional so it may or may not have an implementation in partial classes. In case, the implementation part of a partial method is not available in any partial class, then the compiler will remove the definition of the method and all the calls related to that particular method in the final class.
Following is the example of implementing a partial method using Partial keyword in two class files, User1.vb and User2.vb.
Partial Public Class User
' Partial Method Declaration
Partial Private Sub GetUserDetails(ByVal x As String, ByVal y As String)
End Sub
Public Sub TestMethod()
Console.WriteLine("Test")
End Sub
End Class
If you observe the above code, we declared a partial method called GetUserDetails in partial class (User1.vb) using Partial keyword along with the normal method called TestMethod().
Partial Public Class User
Public Sub New(ByVal a As String, ByVal b As String)
GetUserDetails(a, b)
End Sub
' Partial Method Implementation
Private Sub GetUserDetails(ByVal x As String, ByVal y As String)
Console.WriteLine("Name: " & x)
Console.WriteLine("Location: " & y)
End Sub
End Class
If you observe the above code, we implemented partial method called GetUserDetails in partial class (User2.vb) by duplicating the method signature same as declaration with required variables and constructor.
When we execute the above code, the compiler will combine these two partial classes into one User class like as shown below.
Public Class User
Public Sub New(ByVal a As String, ByVal b As String)
GetUserDetails(a, b)
End Sub
Public Sub TestMethod()
Console.WriteLine("Test")
End Sub
Private Sub GetUserDetails(ByVal x As String, ByVal y As String)
Console.WriteLine("Name: " & x)
Console.WriteLine("Location: " & y)
End Sub
End Class
This is how the compiler will combine all the partial classes into a single class while executing the application in a visual basic programming language.
In visual basic, we need to follow certain rules to implement partial methods in our applications.
artial keyword and method must return void.Private so no access modifiers are allowed and they cannot be Virtual.Following is the example of defining the partial method in partial class using Partial modifier in a visual basic programming language.
Module Module1
Partial Public Class User
' Partial Method Declaration
Partial Private Sub GetUserDetails(ByVal x As String, ByVal y As String)
End Sub
End Class
Partial Public Class User
Public Sub New(ByVal a As String, ByVal b As String)
GetUserDetails(a, b)
End Sub
' Partial Method Implementation
Private Sub GetUserDetails(ByVal x As String, ByVal y As String)
Console.WriteLine("Name: " & x)
Console.WriteLine("Location: " & y)
End Sub
End Class
Sub Main()
Dim u As User = New User("Suresh Dasari", "Hyderabad")
Console.WriteLine("Press Enter Key to Exit..")
Console.ReadLine()
End Sub
End Module
If you observe the above example, we created a partial method called GetUserDetails in two partial classes using Partial keyword to perform the required operations.
When we execute the above visual basic program, we will get the result as shown below.
This is how we can use the partial methods in partial class or structure when we have a method declaration and implementation in multiple files based on our requirements.