' The following HTML code can be used to call the user control in this sample.
'
'		<OBJECT id="usercontrol" classid="usercontrol.dll#UserControl.UserControl1" width="800"
'		height="300" style="font-size:12;">
' 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.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

' 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


    ' 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


    ' 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

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

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