.NET (Core and Framework)

public partial class MainWindow : Window
   {
       public MainWindow()
       {
           InitializeComponent();
       }
       public Window2 window2instance2 { get; set; }



       public void ChangeButton1Content()

       {



        if (window2instance2.key)
           {
               Button1.Content = "I Changed";

           }
       }

       private void Openwindows2_Click(object sender, RoutedEventArgs e)
       {
           Window2 window2instance = new Window2();
           window2instance.MainWindowInstance = this;
           window2instance.Show();

       }

   }

public partial class Window2 : Window
{
    public Window2()
    {
        InitializeComponent();
    }

    public bool key = false;
    public MainWindow MainWindowInstance { get; set; }


   public void window2button_Click(object sender, RoutedEventArgs e)
    {
         MainWindow mainwindow = new MainWindow();
        mainwindow.window2instance2 = this;
        key = true;


        MainWindowInstance.ChangeButton1Content();

        this.Close();
    }
}

<br />
  Try<br />
            ' if the UNCPath end with a backslash then we need to remove it.<br />
            If UNCPath.EndsWith("\") Then<br />
                UNCPath = UNCPath.Remove(UNCPath.Length - 1, 1)<br />
           End If<br />
            Dim nr As NETRESOURCE<br />
            nr = New NETRESOURCE<br />
            nr.lpRemoteName = UNCPath<br />
            nr.lpLocalName = DriveLetter ":"<br />
            strUsername = My.Settings.ServiceDomain & My.Settings.ServiceID.ToString<br />
            strPassword = My.Settings.ServicePassword.ToString<br />
            nr.dwType = RESOURCETYPE_DISK<br />
            Dim result As Integer<br />
            result = WNetAddConnection2(nr, strPassword, strUsername, 0)<br />
            If result = 0 Then<br />
                      Return True<br />
<br />
            Else<br />
                Select Case result<br />
                    Case 53 'Network path not found<br />
                                              Throw New Exception("Network path not found.")<br />
                    Case Else<br />
                          Throw New Exception("Unknown error mapping drive. Return result=" & result.ToString & "; lpRemoteName=" & nr.lpRemoteName & "; lpLocalName=" & nr.lpLocalName & "; strUsername=" & strUsername & "; strPassword=" & strPassword)<br />
                End Select<br />
<br />
                Return False<br />
<br />
            End If<br />