无法弄清楚如何从单独的.xaml窗口更新文本框控件

Question

The question implies I'm brand new to WPF, and I am having a lot of problems so far transitioning from winforms.

What I'm trying to do is a very simple concept, but I'm spinning in circles trying to get it to work. I want to have a textbox on my MainWindow update from a property on my 2nd window. However, this window is not open all the time.

In MainWindow, I open up a new window from an event like so:

private void menuChangeSerialPort_Click(object sender, RoutedEventArgs e)
    {
        ChangeSerialPort changeSerialPort = new ChangeSerialPort();
        changeSerialPort.Show();
    }

The purpose of the new window is to give the user the option to change serial ports. I scan them and put them into a combo box. Upon selecting one and confirming (pressing an 'OK' button), I want to send back the string of the serial port name for the MainWindow.xaml to use in the future. I close my 2nd window after that:

public partial class ChangeSerialPort : Window
{
    public ChangeSerialPort()
    {
        InitializeComponent();

        // Used with XAML, the owner is set so the opening position is centered according to where the Main Window is.
        this.Owner = Application.Current.MainWindow;

        // Scan and list port names
        GetSerialPorts(); 
    }

    private string _portname;
    public string serialPortName { get { return _portname; } } // Readonly property


private void serialPortOKBtn_Click(object sender, RoutedEventArgs e)
    {
        txt_noSerialSelected.Visibility = Visibility.Hidden;
        if (cmbbox_serialPortList.SelectedItem == null)
        {
            txt_noSerialSelected.Visibility = Visibility.Visible;
        }
        else
        {
            _portname = cmbbox_serialPortList.SelectedItem.ToString();
           //
           // WHAT TO PUT??
           //
            this.Close();
        }
    }

I cannot for the life of me get data binding to work. I understand this is the proper way, but I have spent a number of hours reading and getting no where. My backup plan is to access the data from a property. But I do not know how to access any properties back on MainWindow, or vice versa (because the window will close after the selection is confirmed). So I'm 0/2.

Can anyone help me out? And possibly explain in very simple terms how databinding could help me out in this scenario? For instance, what are the steps to take and what exactly would go into the textbox xaml on my MainWindow?

<TextBox x:Name="serialPortInUse" Text="?????????" HorizontalAlignment="Right" Margin="0" VerticalAlignment="Top" Height="20" Width="86" TextChanged="serialPortInUse_TextChanged" BorderThickness="0"/>

Thanks in advance!

Answer 1

Any number of ways of doing this, but the simplest (from your POV) is:

1. The second window raises an event when the port is selected. The eventargs would contain the name of the selected port.
2. When the main window creates second one, it subscribes to the event, using a new method to receive the event.
3. When the main window receives the event, set sets the text of serialPortInUse

This is fine for a little app (in the sense of not many windows) as this looks to be. In more complicated apps, I recommend you use the MVVM pattern. There is a very good book about it, Advanced MVVM , which has been around a while now but is still a superb introduction. With MVVM you can use frameworks like MVVMLite - which you can also install via NuGet install-package MVVMLight - which has a Messaging system built in which decouples senders from listeners and would be a natural in this situation.

Answer 2

Add a ref parameter in your ChangeSerialPort window;

public partial class ChangeSerialPort : Window
    {
        TextBox textBox;
        public ChangeSerialPort( TextBox myTextBox)
        {
            InitializeComponent();
            textBox = myTextBox;
        }
    }

Pass that textbox

private void menuChangeSerialPort_Click(object sender, RoutedEventArgs e)
{
    ChangeSerialPort changeSerialPort = new ChangeSerialPort(serialPortInUse);
    changeSerialPort.Show();
}

set the text value

private void serialPortOKBtn_Click(object sender, RoutedEventArgs e)
        {
            txt_noSerialSelected.Visibility = Visibility.Hidden;
            if (cmbbox_serialPortList.SelectedItem == null)
            {
                txt_noSerialSelected.Visibility = Visibility.Visible;
            }
            else
            {
                _portname = cmbbox_serialPortList.SelectedItem.ToString();
                textBox.Text = _portname;
                this.Close();
            }
        }