[Aly El-Haddad]

و عليكم السلام و رحمة الله و بركاته،

كود :

Public Class Form1
    Dim S As String = "Some string!"

    Private Sub Form1_KeyUp(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyUp
        If e.KeyCode = Keys.Escape Then
            MsgBox("Before: " & S)
            S = Nothing
            MsgBox("After: " & S)
        End If
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Me.KeyPreview = True
    End Sub
End Class