SecureString.MakeReadOnly 方法

定義

命名空間:

System.Security

組件:

System.Runtime.InteropServices.dll

來源:

SecureString.cs

使這個安全字串的文字值成為唯讀。

public:
 void MakeReadOnly();

public void MakeReadOnly ();

member this.MakeReadOnly : unit -> unit

Public Sub MakeReadOnly ()

例外狀況

ObjectDisposedException

這個安全字串已經過處置。

範例

下列範例示範如何使用 AppendChar 和 RemoveAt 方法來收集密碼中的字元。 收集密碼之後，會變成隻讀。

using namespace System;
using namespace System::Security;

void main()
{
   bool go = true;
   ConsoleKeyInfo cki;
   String^ m = L"\nEnter your password (up to 15 letters, numbers, and underscores)\n"
               L"Press BACKSPACE to delete the last character entered. " +
               L"\nPress Enter when done, or ESCAPE to quit:";
   SecureString ^ password = gcnew SecureString;
   int top;
   int 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;

   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.
   delete password;

}
// 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:
//    ************

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 Example
   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:
'    ************

備註

使用建構函式初始化 類別實例的 SecureString 文字值，並使用 、 RemoveAt 、 SetAtInsertAt 和 AppendChar 方法修改值 Clear 。 SecureString

完成最終修改之後，請使用 MakeReadOnly 方法，將實例的值設為不可變 (唯讀) 。 將值標示為唯讀之後，任何進一步的修改嘗試都會 InvalidOperationException 擲回 。

叫用 MakeReadOnly 的效果是永久性的， SecureString 因為 類別無法讓安全字串再次修改。 IsReadOnly使用 方法來測試 的 SecureString 實例是否為唯讀。

另請參閱

• IsReadOnly()