C# WPF - Want to open multiple windows at once, but only one instance of each window

Question

I am new to WPF and have been hunting for an answer, surely this is not difficult?

I have created a main window with links to multiple windows, and I want them to run modelessly alongside one another, but I don't want to open multiple instances of the SAME window.

In simple terms, I can have Windows A, B, C open at once, but not Windows, A, A, B, C, C.

I need to implement a check for the window I'm trying to open (in this case, EditSettings).

If open - activate it

if not open, open it.

I have the following code in Main, which is not working.

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

    private void MenuItem_Click(object sender, RoutedEventArgs e)
    {
        EditSettings winEditSettings = new EditSettings();
        string isOpen = null;
        if (isOpen == "true")
        {
            winEditSettings.Activate();
        }
        else
        { 
            winEditSettings.Show();
            isOpen = "true";
        }
    }

}

Now I know what's wrong with this logic - every time I press the button to open EditSettings, it's setting isOpen to null again. If I don't set a value to isOpen, the If condition breaks.

I could initialise the variable 'isOpen' as a public variable outside the MenuItem_Click method, but then I think I would need an isOpen variable for each window I create!! Surely there is a better way?

The other option I tried is:

    private void MenuItem_Click(object sender, RoutedEventArgs e)
    {
        EditSettings winEditSettings = new EditSettings();
        if (winEditSettings.IsLoaded)
        {
            winEditSettings.Activate();
        }
        else { winEditSettings.Show(); }

I can't figure out why this isn't working, I tried isVisible, isLoaded, isActive - nothing is stopping the window from opening more than once. Thank you for the help!

Answer 1

               if (_adCst == null)
               {
            _adCst = new AddCustomerPage();
            _adCst.WindowStartupLocation = System.Windows.WindowStartupLocation.CenterScreen;
            _adCst.WindowState = System.Windows.WindowState.Normal;
            _adCst.ResizeMode = System.Windows.ResizeMode.NoResize;
            _adCst.Activate();  // This may need to be inside the block above
            _adCst.Show();
               }

              else
        {
            if (!_adCst.IsLoaded == true) 
            {
                _adCst = new AddCustomerPage();
                _adCst.WindowStartupLocation = System.Windows.WindowStartupLocation.CenterScreen;
                _adCst.WindowState = System.Windows.WindowState.Normal;
                _adCst.ResizeMode = System.Windows.ResizeMode.NoResize;
                _adCst.Show();
            }

            _adCst.Activate();
        }

Answer 2

For anyone else with this question, I have found another solution - which works except that it doesn't manage to bring the open window to the front (Activate). It does, however, prevent opening the same window more than once.

        foreach (Window n in Application.Current.Windows)
            if (n.Name == "winEditSettings")
            { winEditSettings.Activate(); }
            else
            { winEditSettings.Show(); }

Can anyone speculate on why the window is not brought to the front, with Activate()?

EDIT

For others with this question, placing the winEditSettings.Activate() outside of the foreach loop does everything I'm trying to achieve:

        foreach (Window n in Application.Current.Windows)
            if (n.Name == "winEditSettings")
            { }
            else
            { winEditSettings.Show(); }

    winEditSettings.Activate(); 

This will stop multiple instances of the same window from opening, and will bring the window to the front if the user attempts to reopen it.

Answer 3

There are people who'll perhaps throw a fit at the idea, but whenever I've needed to do this, I made the child window objects part of the application. Then, in your MenuItem_Click(), test if winEditSettings is null, instead.

It's still a member variable for each window (like your provisional isOpen solution), but having the window objects available can have advantages later, if you need to bridge information between the windows. In my cases, we wanted to be able to close all the child windows together, which (most trivially) meant keeping track of those objects in a central location.

Alternatively, if you want the setup completely decoupled, you could take a singleton-like approach and put the logic into your child window classes. Specifically, you could call EditSettings.Activate and let the class keep track of whether a window needs to be created or the existing window merely Show()n.

If I were handed your code to rewrite, I'd move it something like this:

private static EditSettings winEditSettings = null;

public static void WakeUp()
{
    if (winEditSettings == null)
    {
        winEditSettings = new EditSettings();
    }
    winEditSettings.Activate();  // This may need to be inside the block above
    winEditSettings.Show();
}

Both of those are part of the class (static), rather than an instance. Your application object therefore calls EditSettings.WakeUp() inside the original MenuItem_Click(), and never actually sees the child window, itself.

If you change your mind about the decoupled architecture later, by the way, you can add a get accessor to your winEditSettings and keep everybody fairly happy.

Answer 4

My suggestion would be that you set some form of a counter. This will prevent more than one instance of the window being opened.

    int windowOpen = 1;

    private void button_Click(object sender, RoutedEventArgs e)
    {        
        if (windowOpen == 1) 
        {
            WindowA winA = new WindowA();
            winA.Show();
            windowOpen++; //increments windowOpen by 1, windowOpen will now = 2
        }
        else if (windowOpen > 1)
        {
            MessageBox.Show("Window is already open"); 
        }
    }

I hope this helps.