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AllowPartiallyTrustedCallersAttribute Class

Allows strong-named assemblies to be called by partially trusted code. Without this declaration, only fully trusted callers are able to use such assemblies. This class cannot be inherited.

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

'Declaration
<ComVisibleAttribute(True)> _
<AttributeUsageAttribute(AttributeTargets.Assembly, AllowMultiple := False,  _
	Inherited := False)> _
Public NotInheritable Class AllowPartiallyTrustedCallersAttribute _
	Inherits Attribute
'Usage
Dim instance As AllowPartiallyTrustedCallersAttribute

AllowPartiallyTrustedCallersAttribute is only effective when applied by a strong-named assembly at the assembly level. For more information about applying attributes at the assembly level, see Applying Attributes.

By default, a strong-named assembly that does not explicitly apply this attribute at assembly level to allow its use by partially trusted code can be called only by other assemblies that are granted full trust by security policy. This restriction is enforced by placing a LinkDemand for FullTrust on every public or protected method on every publicly accessible class in the assembly. Assemblies that are intended to be called by partially trusted code can declare their intent through the use of the AllowPartiallyTrustedCallersAttribute. The attribute is declared at the assembly level. An example of the declaration in C# is [assembly:AllowPartiallyTrustedCallers] and in Visual Basic is <assembly:AllowPartiallyTrustedCallers>.

Caution noteCaution:

The presence of this assembly-level attribute prevents the default behavior of placing FullTrust  LinkDemand security checks, making the assembly callable from any other assembly (partially or fully trusted).

When this attribute is present, all other security checks function as intended, including any class-level or method-level declarative security attributes that are present. This attribute blocks only the implicit fully trusted caller demand.

This is not a declarative security attribute, but a regular attribute (it derives from Attribute, not SecurityAttribute).

For more information, see Using Libraries from Partially Trusted Code.

The following example shows the use of the AllowPartiallyTrustedCallersAttribute class.

' The following HTML code can be used to call the user control in this sample. 

'<HTML> 
'	<BODY> 
'		<OBJECT id="usercontrol" classid="usercontrol.dll#UserControl.UserControl1" width="800" 
'		height="300" style="font-size:12;"> 
'		</OBJECT> 
'		<p> 
'	</BODY> 
'</HTML> 
' To run this test control you must create a strong name key, snkey.snk, and  
' a code group that gives full trust to assemblies signed with snkey.snk. 
' The user control displays an OpenFileDialog box, then displays a text box containing the name of  
' the file selected and a list box that displays the contents of the file.  The selected file must  
' contain text in order for the control to display the data properly. 
' Caution  This sample demonstrates the use of the Assert method.  Calling Assert removes the  
' requirement that all code in the call chain must be granted permission to access the specified  
' resource, it can open up security vulnerabilities if used incorrectly or inappropriately. Therefore,  
' it should be used with great caution.  Assert should always be followed with a RevertAssert  
' command to restore the security settings. 

Imports System
Imports System.Collections
Imports System.ComponentModel
Imports System.Drawing
Imports System.Data
Imports System.Windows.Forms
Imports System.IO
Imports System.Security
Imports System.Security.Permissions
Imports System.Reflection
Imports System.Runtime.CompilerServices
Imports Microsoft.VisualBasic


' This strong name key is used to create a code group that gives permissions to this assembly.

<Assembly: AssemblyKeyFile("snKey.snk")> 

<Assembly: AssemblyVersion("1.0.0.0")> 
' The AllowPartiallyTrustedCallersAttribute requires the assembly to be signed with a strong name key. 
' This attribute is necessary since the control is called by either an intranet or Internet 
' Web page that should be running under restricted permissions.

<Assembly: AllowPartiallyTrustedCallers()> 

' The userControl1 displays an OpenFileDialog box, then displays a text box containing the name of  
' the file selected and a list box that displays the contents of the file.  The selected file must  
' contain text in order for the control to display the data properly. 

'Demand the zone requirement for the calling application.
<ZoneIdentityPermissionAttribute(SecurityAction.Demand, Zone:=SecurityZone.Intranet)> _
Public Class UserControl1
    Inherits System.Windows.Forms.UserControl
    Private WithEvents textBox1 As System.Windows.Forms.TextBox
    Private listBox1 As System.Windows.Forms.ListBox
    ' Required designer variable. 
    Private components As System.ComponentModel.Container = Nothing 


    Public Sub New()
        ' This call is required by the Windows.Forms Form Designer.
        InitializeComponent()

        ' The OpenFileDialog box should not require any special permissions. 
        Dim fileDialog As New OpenFileDialog
        If fileDialog.ShowDialog() = DialogResult.OK Then 
            ' Reading the name of the selected file from the OpenFileDialog box 
            ' and reading the file requires FileIOPermission.  The user control should  
            ' have this permission granted through its code group; the Web page that calls the  
            ' control should not have this permission.  The Assert command prevents a stack walk  
            ' that would fail because the caller does not have the required FileIOPermission.   
            ' The use of Assert can open up security vulnerabilities if used incorrectly or  
            ' inappropriately. Therefore, it should be used with great caution. 
            ' The Assert command should be followed by a RevertAssert as soon as the file operation  
            ' is completed. 
            Dim fileIOPermission As New FileIOPermission(PermissionState.Unrestricted)
            fileIOPermission.Assert()
            textBox1.Text = fileDialog.FileName
            ' Display the contents of the file in the text box. 
            Dim fsIn As New FileStream(textBox1.Text, FileMode.Open, FileAccess.Read, FileShare.Read)
            Dim sr As New StreamReader(fsIn)

            ' Process every line in the file 
            Dim Line As String
            Line = sr.ReadLine()
            While Not (Line Is Nothing)
                listBox1.Items.Add(Line)
                Line = sr.ReadLine()
            End While 
            ' It is very important to call RevertAssert to restore the stack walk for 
            ' file operations.
            fileIOPermission.RevertAssert()
        End If 
    End Sub 'New 


    ' Clean up any resources being used. 
    Protected Overloads Sub Dispose(ByVal disposing As Boolean)
        If disposing Then 
            If Not (components Is Nothing) Then
                components.Dispose()
            End If 
        End If 
        MyBase.Dispose(disposing)
    End Sub 'Dispose


    ' Required method for Designer support - do not modify  
    ' the contents of this method with the code editor. 
    Private Sub InitializeComponent()
        Me.textBox1 = New System.Windows.Forms.TextBox
        Me.listBox1 = New System.Windows.Forms.ListBox
        Me.SuspendLayout()
        '  
        ' textBox1 
        '  
        Me.textBox1.Location = New System.Drawing.Point(208, 112)
        Me.textBox1.Name = "textBox1" 
        Me.textBox1.Size = New System.Drawing.Size(320, 20)
        Me.textBox1.TabIndex = 0
        Me.textBox1.Text = "textBox1" 
        '  
        ' listBox1 
        '  
        Me.listBox1.Location = New System.Drawing.Point(200, 184)
        Me.listBox1.Name = "listBox1" 
        Me.listBox1.Size = New System.Drawing.Size(336, 108)
        Me.listBox1.TabIndex = 1
        '  
        ' UserControl1 
        '  
        Me.Controls.Add(listBox1)
        Me.Controls.Add(textBox1)
        Me.Name = "UserControl1" 
        Me.Size = New System.Drawing.Size(592, 400)
        Me.ResumeLayout(False)
    End Sub 'InitializeComponent

    Private Sub UserControl1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
    End Sub 'UserControl1_Load

    Private Sub textBox1_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles textBox1.TextChanged
    End Sub 'textBox1_TextChanged
End Class 'UserControl1 

System.Object
  System.Attribute
    System.Security.AllowPartiallyTrustedCallersAttribute

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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

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