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This article mainly shows you "VB.NET how to use optional parameters", the content is easy to understand, clear, hope to help you solve your doubts, the following let the editor lead you to study and learn "VB.NET how to use optional parameters" this article.

As an object-oriented programming language developed by Microsoft, VB.NET can provide a stable and reliable development environment for programmers and further improve the efficiency of program development. First, let's take a look at the concepts related to the VB.NET optional parameters. You can specify that procedure parameters are optional and do not have to provide variables for them when the procedure is called. Optional parameters are indicated by the keyword Optional in the procedure definition. The following rules apply:

Each optional parameter in the procedure definition must specify a default value.

The default value of the VB.NET optional parameter must be a constant expression.

Each parameter that follows the optional parameter in the process definition must also be optional.

The following syntax shows the procedure declaration with optional parameters:

Sub sub name (ByVal parameter

1 As data type 1, Optional

ByVal parameter 2 As data

Type 2 = default value)

Call a procedure with optional parameters

When calling a procedure with optional parameters, you can choose whether or not to provide the variable. If not provided, the procedure uses the default value declared for the parameter.

When one or more VB.NET optional parameters in the parameter list are omitted, their positions are marked with consecutive commas. The following invocation example provides * * and the fourth argument, omitting the second and third:

Call sub name (argument

1, argument 4)

Determine if optional parameters exist

The procedure cannot detect at run time whether the given parameter has been omitted or whether the calling code has explicitly provided a default value. If you need to figure this out, you can set an impossible value as the default. The following procedure defines the optional parameter office and tests its default value, QJZ, to see if it has been omitted in the call:

Visual Basic

Sub notify (ByVal company As String

Optional ByVal office As String =

"QJZ") If office = "QJZ" Then Debug

WriteLine ("office not supplied--

Using Headquarters ") office =

"Headquarters" End If 'Insert code

To notify headquarters or specified

Office.End Sub

If the VB.NET optional parameter is a reference type such as String, you can use Nothing as the default value as long as it is not the expected value of the variable.

Optional parameters and overload

Another way to define a procedure with optional parameters is to use overloading. If you have an optional parameter, you can define two overloaded versions of the procedure, one accepting this parameter and the other without it. This method becomes more complex as the number of optional parameters increases. However, the advantage of this is that you can fully determine whether the caller provides each VB.NET optional parameter.

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