Статья
11/18/2011

Type.Missing Field

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Represents a missing value in the Type information. This field is read-only.

Namespace: System
Assembly: mscorlib (in mscorlib.dll)

Syntax

'Declaration
Public Shared ReadOnly Missing As Object

public static readonly Object Missing

Remarks

Use the Missing field for invocation through reflection to obtain the default value of a parameter. If the Missing field is passed in for a parameter value and there is no default value for that parameter, an ArgumentException is thrown.

Platform Notes

Silverlight for Windows Phone

The Type.Missing field does not throw ArgumentException when the called method has no default value for a parameter.

Examples

The following code example shows the use of the Missing field to invoke a method with its default arguments.

There is no C# example, because C# cannot declare optional parameters.

Note:
To run this example, see Building Examples That Use a Demo Method and a TextBlock Control.

Option Strict Off
Imports System.Reflection

Public Class OptionalArg
   Public Function MyMethod(ByVal a As Integer, _
      Optional ByVal b As Double = 1.2, Optional ByVal c As Integer = 1) As String

      Return "a = " & a & " b = " & b & " c = " & c 
   End Function
End Class

Public Class Example
   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim o As New OptionalArg()
      Dim binding As BindingFlags = BindingFlags.Public Or BindingFlags.Instance Or _
         BindingFlags.InvokeMethod Or BindingFlags.OptionalParamBinding
      Dim t As Type = GetType(OptionalArg)
      Dim param As Object() = {10, 20, 30}

      Dim result As Object = _
         t.InvokeMember("MyMethod", binding, Nothing, o, New Object() {10, 55.3, 12})
      outputBlock.Text &= result & vbLf

      result = _
         t.InvokeMember("MyMethod", binding, Nothing, o, New Object() {10, 55.3, Type.Missing})
      outputBlock.Text &= result & vbLf

      result = _ 
         t.InvokeMember("MyMethod", binding, Nothing, o, New Object() {10, Type.Missing, Type.Missing})
      outputBlock.Text &= result & vbLf
   End Sub
End Class

' This example produces the following output:
'
'a = 10 b = 55.3 c = 12
'a = 10 b = 55.3 c = 1
'a = 10 b = 1.2 c = 1

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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