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how-to-pass-procedures-to-another-procedure.md

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Learn more about: How to: Pass Procedures to Another Procedure in Visual Basic
How to: Pass Procedures to Another Procedure
07/20/2015
AddressOf operator [Visual Basic]
delegates [Visual Basic], passing procedures
5adbba15-5a1d-413f-ab3e-3ff6cc0a4669

How to: Pass Procedures to Another Procedure in Visual Basic

This example shows how to use delegates to pass a procedure to another procedure.

A delegate is a type that you can use like any other type in Visual Basic. The AddressOf operator returns a delegate object when applied to a procedure name.

This example has a procedure with a delegate parameter that can take a reference to another procedure, obtained with the AddressOf operator.

Create the delegate and matching procedures

  1. Create a delegate named MathOperator.

    [!code-vbVbVbalrDelegates#1]

  2. Create a procedure named AddNumbers with parameters and return value that match those of MathOperator, so that the signatures match.

    [!code-vbVbVbalrDelegates#2]

  3. Create a procedure named SubtractNumbers with a signature that matches MathOperator.

    [!code-vbVbVbalrDelegates#3]

  4. Create a procedure named DelegateTest that takes a delegate as a parameter.

    This procedure can accept a reference to AddNumbers or SubtractNumbers, because their signatures match the MathOperator signature.

    [!code-vbVbVbalrDelegates#4]

  5. Create a procedure named Test that calls DelegateTest once with the delegate for AddNumbers as a parameter, and again with the delegate for SubtractNumbers as a parameter.

    [!code-vbVbVbalrDelegates#5]

    When Test is called, it first displays the result of AddNumbers acting on 5 and 3, which is 8. Then the result of SubtractNumbers acting on 9 and 3 is displayed, which is 6.

See also