SecureString.MakeReadOnly Metod

public:
 void MakeReadOnly();

public void MakeReadOnly();

member this.MakeReadOnly : unit -> unit

Public Sub MakeReadOnly ()

Undantag

Exempel

I följande exempel visas hur AppendChar metoderna och RemoveAt kan användas för att samla in tecknen i ett lösenord. När lösenordet har samlats in görs det skrivskyddat.

using System;
using System.Security;

class Example
{
   public static void Main()
   {
      ConsoleKeyInfo cki;
      String m = "\nEnter your password (up to 15 letters, numbers, and underscores)\n" +
                 "Press BACKSPACE to delete the last character entered. " +
                 "\nPress Enter when done, or ESCAPE to quit:";
      SecureString password = new SecureString();
      int top, left;

      // The Console.TreatControlCAsInput property prevents CTRL+C from
      // ending this example.
      Console.TreatControlCAsInput = true;

      Console.Clear();
      Console.WriteLine(m);

      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.

      do {
         cki = Console.ReadKey(true);
         if (cki.Key == ConsoleKey.Escape) break;

         if (cki.Key == ConsoleKey.Backspace) {
            if (password.Length > 0) {
               Console.SetCursorPosition(left + password.Length - 1, top);
               Console.Write(' ');
               Console.SetCursorPosition(left + password.Length - 1, top);
               password.RemoveAt(password.Length-1);
            }
         }
         else {
            if ((password.Length < 15) &&
                 (Char.IsLetterOrDigit(cki.KeyChar) || cki.KeyChar == '_')) {
               password.AppendChar(cki.KeyChar);
               Console.SetCursorPosition(left+password.Length-1, top);
               Console.Write('*');
            }
         }
      } while (cki.Key != ConsoleKey.Enter & password.Length < 15);

      // Make the password read-only to prevent modification.
      password.MakeReadOnly();
      // Dispose of the SecureString instance.
      password.Dispose();
   }
}
// This example displays output like the following:
//    Enter your password (up to 15 letters, numbers, and underscores)
//    Press BACKSPACE to delete the last character entered.
//    Press Enter when done, or ESCAPE to quit:
//    ************

Imports System.Security

Class ExampleClass
   Public Shared Sub Main()
      Dim cki As ConsoleKeyInfo
      Dim m As String = vbCrLf & "Enter your password (up to 15 letters, numbers, and underscores)" &
                        vbCrLf & "Press BACKSPACE to delete the last character entered. " & vbCrLf &
                        "Press Enter when done, or ESCAPE to quit: "
      Dim password As New SecureString()
      Dim top, left As Integer

      ' The Console.TreatControlCAsInput property prevents CTRL+C from
      ' ending this example.
      Console.TreatControlCAsInput = True

      Console.Clear()
      Console.WriteLine(m)

      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.

      Do
         cki = Console.ReadKey(True)
         If cki.Key = ConsoleKey.Escape Then Exit Do

         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
      Loop While cki.Key <> ConsoleKey.Enter And password.Length < 15

      ' Make the password read-only to prevent modification.
      password.MakeReadOnly()
      ' Dispose of the SecureString instance.
      password.Dispose()
   End Sub
End Class
' The example displays output like the following:
'    Enter your password (up to 15 letters, numbers, and underscores)
'    Press BACKSPACE to delete the last character entered.
'    Press Enter when done, or ESCAPE to quit:
'    ************

Kommentarer

Initiera textvärdet för en instans av SecureString klassen med SecureString konstruktorerna och ändra värdet med Clearmetoderna , , RemoveAtSetAt, InsertAtoch AppendChar .

När du har gjort dina sista ändringar använder du MakeReadOnly metoden för att göra värdet för instansen oföränderlig (skrivskyddad). När värdet har markerats som skrivskyddat genererar alla ytterligare försök att ändra det en InvalidOperationException.

Effekten av att MakeReadOnly anropa är permanent eftersom SecureString klassen inte ger något sätt att göra den säkra strängen ändringsbar igen. IsReadOnly Använd metoden för att testa om en instans av SecureString är skrivskyddad.

Se även

• IsReadOnly()