// 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.
using System;
using System.Collections;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Windows.Forms;
using System.IO;
using System.Security;
using System.Security.Permissions;
using System.Reflection;
using 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]
namespace UserControl
{
// 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.
public class UserControl1 : System.Windows.Forms.UserControl
{
private System.Windows.Forms.TextBox textBox1;
private System.Windows.Forms.ListBox listBox1;
// Required designer variable.
private System.ComponentModel.Container components = null;
// Demand the zone requirement for the calling application.
[ZoneIdentityPermission(SecurityAction.Demand, Zone = SecurityZone.Intranet)]
public UserControl1()
{
// This call is required by the Windows.Forms Form Designer.
InitializeComponent();
// The OpenFileDialog box should not require any special permissions.
OpenFileDialog fileDialog = new OpenFileDialog();
if(fileDialog.ShowDialog() == DialogResult.OK)
{
// 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.
new FileIOPermission(PermissionState.Unrestricted).Assert();
textBox1.Text = fileDialog.FileName;
// Display the contents of the file in the text box.
FileStream fsIn = new FileStream(textBox1.Text, FileMode.Open, FileAccess.Read,
FileShare.Read);
StreamReader sr = new StreamReader(fsIn);
// Process every line in the file
for (String Line = sr.ReadLine(); Line != null; Line = sr.ReadLine())
{
listBox1.Items.Add(Line);
}
// It is very important to call RevertAssert to restore the stack walk for
// file operations.
FileIOPermission.RevertAssert();
}
}
// Clean up any resources being used.
protected override void Dispose( bool disposing )
{
if( disposing )
{
if( components != null )
components.Dispose();
}
base.Dispose( disposing );
}
#region Component Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.textBox1 = new System.Windows.Forms.TextBox();
this.listBox1 = new System.Windows.Forms.ListBox();
this.SuspendLayout();
//
// textBox1
//
this.textBox1.Location = new System.Drawing.Point(208, 112);
this.textBox1.Name = "textBox1";
this.textBox1.Size = new System.Drawing.Size(320, 20);
this.textBox1.TabIndex = 0;
this.textBox1.Text = "textBox1";
this.textBox1.TextChanged += new System.EventHandler(this.textBox1_TextChanged);
//
// listBox1
//
this.listBox1.Location = new System.Drawing.Point(200, 184);
this.listBox1.Name = "listBox1";
this.listBox1.Size = new System.Drawing.Size(336, 108);
this.listBox1.TabIndex = 1;
//
// UserControl1
//
this.Controls.Add(this.listBox1);
this.Controls.Add(this.textBox1);
this.Name = "UserControl1";
this.Size = new System.Drawing.Size(592, 400);
this.Load += new System.EventHandler(this.UserControl1_Load);
this.ResumeLayout(false);
