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IPermission Interface

Defines methods implemented by permission types.

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

<ComVisibleAttribute(True)> _
Public Interface IPermission _
	Inherits ISecurityEncodable
Dim instance As IPermission

Permissions in the common language runtime are objects that describe sets of operations that can be secured for specified resources. A permission object describes operations or access that is subject to security control; it does not represent access or a right to perform operations. Permissions are used by both application code and the .NET Framework security system in the following ways.

  • Code requests the permissions it needs in order to run.

  • The security system policy grants permissions to code in order for it to run.

  • Code demands that calling code has a permission.

  • Code overrides the security stack using assert/deny/permit-only.


If you write a new permission, you must implement this interface in your class.

Important noteImportant Note:

A permission can be accessed by multiple threads. When implementing this interface, you must guarantee that the IsSubsetOf, Intersect, Union, and Copy method implementations are thread safe.

This example shows how to define a permission class for use with code access security. All of the necessary permission interfaces are implemented.

Imports System
Imports System.Security
Imports System.Security.Permissions
Imports System.Reflection

' Enumerated type for permission states.
<Serializable()>  _
Public Enum SoundPermissionState
    NoSound = 0
    PlaySystemSounds = 1
    PlayAnySound = 2
End Enum 'SoundPermissionState

' Derive from CodeAccessPermission to gain implementations of the following 
' sealed IStackWalk methods: Assert, Demand, Deny, and PermitOnly. 
' Implement the following abstract IPermission methods: Copy, Intersect, and IsSubSetOf. 
' Implementing the Union method of the IPermission class is optional. 
' Implement the following abstract ISecurityEncodable methods: FromXml and ToXml. 
' Making the class 'sealed' is optional. 

NotInheritable Public Class SoundPermission
    Inherits CodeAccessPermission
    Implements IPermission, IUnrestrictedPermission, ISecurityEncodable, ICloneable
    Private m_specifiedAsUnrestricted As [Boolean] = False 
    Private m_flags As SoundPermissionState = SoundPermissionState.NoSound
    ' This constructor creates and initializes a permission with generic access. 
    Public Sub New(ByVal state As PermissionState) 
        m_specifiedAsUnrestricted = state = PermissionState.Unrestricted

    End Sub 'New     
    ' This constructor creates and initializes a permission with specific access.         
    Public Sub New(ByVal flags As SoundPermissionState) 
        If Not [Enum].IsDefined(GetType(SoundPermissionState), flags) Then 
            Throw New ArgumentException("flags value is not valid for the SoundPermissionState enuemrated type")
        End If
        m_specifiedAsUnrestricted = False
        m_flags = flags

    End Sub 'New    
    ' For debugging, return the state of this object as XML. 
    Public Overrides Function ToString() As String  
        Return ToXml().ToString()

    End Function 'ToString   
    ' Private method to cast (if possible) an IPermission to the type. 
    Private Function VerifyTypeMatch(ByVal target As IPermission) As SoundPermission
        If [GetType]() <> target.GetType() Then 
            Throw New ArgumentException(String.Format("target must be of the {0} type", [GetType]().FullName))
        End If 
        Return CType(target, SoundPermission)

    End Function 'VerifyTypeMatch
    ' This is the Private Clone helper method.  
    Private Function Clone(ByVal specifiedAsUnrestricted As [Boolean], ByVal flags As SoundPermissionState) As SoundPermission
        Dim soundPerm As SoundPermission = CType(Clone(), SoundPermission)
        soundPerm.m_specifiedAsUnrestricted = specifiedAsUnrestricted
        soundPerm.m_flags = IIf(specifiedAsUnrestricted, SoundPermissionState.PlayAnySound, m_flags)
        Return soundPerm

    End Function 'Clone

#Region "IPermission Members" 

    ' Return a new object that contains the intersection of 'this' and 'target'. 
    Public Overrides Function Intersect(ByVal target As IPermission) As IPermission
        ' If 'target' is null, return null. 
        If target Is Nothing Then 
            Return Nothing 
        End If 
        ' Both objects must be the same type. 
        Dim soundPerm As SoundPermission = VerifyTypeMatch(target)

        ' If 'this' and 'target' are unrestricted, return a new unrestricted permission. 
        If m_specifiedAsUnrestricted AndAlso soundPerm.m_specifiedAsUnrestricted Then 
            Return Clone(True, SoundPermissionState.PlayAnySound)
        End If 
        ' Calculate the intersected permissions. If there are none, return null. 
        Dim val As SoundPermissionState = CType(Math.Min(CType(m_flags, Int32), CType(soundPerm.m_flags, Int32)), SoundPermissionState)
        If val = 0 Then 
            Return Nothing 
        End If 
        ' Return a new object with the intersected permission value. 
        Return Clone(False, val)

    End Function 'Intersect

    ' Called by the Demand method: returns true if 'this' is a subset of 'target'. 
    Public Overrides Function IsSubsetOf(ByVal target As IPermission) As [Boolean]
        ' If 'target' is null and this permission allows nothing, return true. 
        If target Is Nothing Then 
            Return m_flags = 0
        End If 
        ' Both objects must be the same type. 
        Dim soundPerm As SoundPermission = VerifyTypeMatch(target)

        ' Return true if the permissions of 'this' is a subset of 'target'. 
        Return m_flags <= soundPerm.m_flags

    End Function 'IsSubsetOf

    ' Return a new object that matches 'this' object's permissions. 
    Public Overrides Function Copy() As IPermission
        Return CType(Clone(), IPermission)

    End Function 'Copy

    ' Return a new object that contains the union of 'this' and 'target'. 
    ' Note: You do not have to implement this method. If you do not, the version 
    ' in CodeAccessPermission does this: 
    '    1. If target is not null, a NotSupportedException is thrown. 
    '    2. If target is null, then Copy is called and the new object is returned. 
    Public Overrides Function Union(ByVal target As IPermission) As IPermission
        ' If 'target' is null, then return a copy of 'this'. 
        If target Is Nothing Then 
            Return Copy()
        End If 
        ' Both objects must be the same type. 
        Dim soundPerm As SoundPermission = VerifyTypeMatch(target)

        ' If 'this' or 'target' are unrestricted, return a new unrestricted permission. 
        If m_specifiedAsUnrestricted OrElse soundPerm.m_specifiedAsUnrestricted Then 
            Return Clone(True, SoundPermissionState.PlayAnySound)
        End If 
        ' Return a new object with the calculated, unioned permission value. 
        Return Clone(False, CType(Math.Max(CType(m_flags, Int32), CType(soundPerm.m_flags, Int32)), SoundPermissionState))

    End Function 'Union
#End Region
#Region "ISecurityEncodable Members" 

    ' Populate the permission's fields from XML. 
    Public Overrides Sub FromXml(ByVal e As SecurityElement)
        m_specifiedAsUnrestricted = False
        m_flags = 0

        ' If XML indicates an unrestricted permission, make this permission unrestricted. 
        Dim s As String = CStr(e.Attributes("Unrestricted"))
        If Not (s Is Nothing) Then
            m_specifiedAsUnrestricted = Convert.ToBoolean(s)
            If m_specifiedAsUnrestricted Then
                m_flags = SoundPermissionState.PlayAnySound
            End If 
        End If 
        ' If XML indicates a restricted permission, parse the flags. 
        If Not m_specifiedAsUnrestricted Then
            s = CStr(e.Attributes("Flags"))
            If Not (s Is Nothing) Then
                m_flags = CType(Convert.ToInt32([Enum].Parse(GetType(SoundPermission), s, True)), SoundPermissionState)
            End If 
        End If 

    End Sub 'FromXml

    ' Produce XML from the permission's fields. 
    Public Overrides Function ToXml() As SecurityElement
        ' These first three lines create an element with the required format. 
        Dim e As New SecurityElement("IPermission")
        ' Replace the double quotation marks (“”) with single quotation marks (‘’) 
        ' to remain XML compliant when the culture is not neutral.
        e.AddAttribute("class", [GetType]().AssemblyQualifiedName.Replace(ControlChars.Quote, "'"c))
        e.AddAttribute("version", "1")

        If Not m_specifiedAsUnrestricted Then
            e.AddAttribute("Flags", [Enum].Format(GetType(SoundPermissionState), m_flags, "G"))
            e.AddAttribute("Unrestricted", "true")
        End If 
        Return e

    End Function 'ToXml
#End Region
#Region "IUnrestrictedPermission Members" 

    ' Returns true if permission is effectively unrestricted. 
    Public Function IsUnrestricted() As [Boolean] Implements IUnrestrictedPermission.IsUnrestricted
        ' This means that the object is unrestricted at runtime. 
        Return m_flags = SoundPermissionState.PlayAnySound

    End Function 'IsUnrestricted
#End Region
#Region "ICloneable Members" 
    ' Return a copy of the permission. 
    Public Function Clone() As [Object] Implements System.ICloneable.Clone
        Return MemberwiseClone()

    End Function 'Clone 
#End Region

End Class 'SoundPermission

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0