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This article mainly introduces how to call VB.NET optional parameters, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let the editor take you to understand it.

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 the optional parameter VB.NET:

Sub sub name (ByVal parameter

1 As data type 1, Optional

ByVal parameter 2 As data

Type 2 = default value)

Call a procedure with VB.NET optional parameters

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 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.

VB.NET 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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