| Title | Use a variable to hold delegates (function pointers) in Visual Basic 2005 |
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| Description | This example shows how to use a variable to hold delegates (function pointers) in Visual Basic 2005. |
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| Keywords | delegate, function pointer, function reference, method pointer, methd reference, Visual Basic 2005 |
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| Categories | Software Engineering, VB.NET |
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A delegate is a variable that can hold a reference to a subroutine or function. This program uses a delegate variable to refer to each of three functions and then calls them.
Here are the three functions. Note that they have the same signature: all take an integer parameter and return an integer result.
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Private Function A(ByVal x As Integer) As Integer
Return x + 1
End Function
Private Function B(ByVal x As Integer) As Integer
Return x * 2
End Function
Private Function C(ByVal x As Integer) As Integer
Return x * x
End Function
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Here's the delegate type definition. Variables of this type can be assigned to any function that takes an integer parameter and returns an integer result.
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Private Delegate Function ABCFunction(ByVal x As Integer) _
As Integer
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Here's the variable declaration. The variable func can refer to a function that takes an integer parameter and returns an integer result.
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Dim func As ABCFunction
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Finally, here's some code that uses the variable. It assigns it to point to each of the three functions and calls each.
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func = AddressOf A
Debug.WriteLine("A: " & func(10))
func = AddressOf B
Debug.WriteLine("B: " & func(10))
func = AddressOf C
Debug.WriteLine("C: " & func(10))
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And here are the results:
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A: 11
B: 20
C: 100
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