Assembly: mscorlib (in mscorlib.dll)
This secure string has already been disposed.
After you have made your final modifications, use the MakeReadOnly method to make the value of the instance immutable (read-only). After the value is marked as read-only, any further attempt to modify it throws an InvalidOperationException.
The effect of invoking MakeReadOnly is permanent because no means is provided to make the secure string modifiable again. Use the IsReadOnly method to test whether an instance of SecureString is read-only.
The following code example demonstrates how the AppendChar and RemoveAt methods can be used to collect the characters in a password. After the password is collected, it is made read-only.
' This example demonstrates using the AppendChar and RemoveAt ' methods to collect a password. Imports System Imports System.Security Class Sample Public Shared Sub Main() Dim cki As ConsoleKeyInfo Dim m1 As String = "(This example simulates entering a password. " & _ "Do not enter an actual password.)" & vbCrLf Dim m2 As String = "Enter your password (up to 15 letters, numbers, and underscores)" & vbCrLf & "Press BACKSPACE to delete the last character entered. " & vbCrLf & _ "Press ESCAPE to quit:" Dim password As New SecureString() Dim top, left As Integer ' ' The Console.TreatControlCAsInput property prevents this example from ' ending if you press CTL+C, however all other operating system keys and ' shortcuts, such as ALT+TAB or the Windows Logo key, are still in effect. ' Each input character is assumed to occupy one screen column. ' Console.TreatControlCAsInput = True Console.Clear() Console.WriteLine(m1) Console.WriteLine(m2) top = Console.CursorTop left = Console.CursorLeft ' Read user input from the console. Store up to 15 letter, digit, or underscore ' characters in a SecureString object, or delete a character if the user enters ' a backspace. Display an asterisk (*) on the console to represent each character ' that is stored. While True cki = Console.ReadKey(True) If cki.Key = ConsoleKey.Escape Then Exit While End If If cki.Key = ConsoleKey.BackSpace Then If password.Length > 0 Then Console.SetCursorPosition(left + password.Length - 1, top) Console.Write(" "c) Console.SetCursorPosition(left + password.Length - 1, top) password.RemoveAt(password.Length - 1) End If Else If password.Length < 15 AndAlso([Char].IsLetterOrDigit(cki.KeyChar) _ OrElse cki.KeyChar = "_"c) Then password.AppendChar(cki.KeyChar) Console.SetCursorPosition(left + password.Length - 1, top) Console.Write("*"c) End If End If End While ' Make the password read-only to prevent it from being modified after it has ' been collected. password.MakeReadOnly() End Sub 'Main End Class 'Sample ' 'This example produces results similar to the following text: ' '(This example simulates entering a password. Do not enter an actual password.) ' 'Enter your password (up to 15 letters, numbers, and underscores) 'Press BACKSPACE to delete the last character entered. 'Press ESCAPE to quit: '*************** '
Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.