[c#] How to hide close button in WPF window?

I'm writing a modal dialog in WPF. How do I set a WPF window to not have a close button? I'd still like for its WindowState to have a normal title bar.

I found ResizeMode, WindowState, and WindowStyle, but none of those properties allow me to hide the close button but show the title bar, as in modal dialogs.

Try adding a Closing event to the window. Add this code to the event handler.

e.Cancel = true;

This will prevent the window from closing. This has the same effect as hiding the close button.

This doesn't hide the button but will prevent the user from moving forward by shutting down the window.

protected override void OnClosing(System.ComponentModel.CancelEventArgs e)
{            
    if (e.Cancel == false)
    {
        Application.Current.Shutdown();
    }
}

I just got to similar problem and Joe White's solution seems to me simple and clean. I reused it and defined it as an attached property of Window

public class WindowBehavior
{
    private static readonly Type OwnerType = typeof (WindowBehavior);

    #region HideCloseButton (attached property)

    public static readonly DependencyProperty HideCloseButtonProperty =
        DependencyProperty.RegisterAttached(
            "HideCloseButton",
            typeof (bool),
            OwnerType,
            new FrameworkPropertyMetadata(false, new PropertyChangedCallback(HideCloseButtonChangedCallback)));

    [AttachedPropertyBrowsableForType(typeof(Window))]
    public static bool GetHideCloseButton(Window obj) {
        return (bool)obj.GetValue(HideCloseButtonProperty);
    }

    [AttachedPropertyBrowsableForType(typeof(Window))]
    public static void SetHideCloseButton(Window obj, bool value) {
        obj.SetValue(HideCloseButtonProperty, value);
    }

    private static void HideCloseButtonChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var window = d as Window;
        if (window == null) return;

        var hideCloseButton = (bool)e.NewValue;
        if (hideCloseButton && !GetIsHiddenCloseButton(window)) {
            if (!window.IsLoaded) {
                window.Loaded += HideWhenLoadedDelegate;
            }
            else {
                HideCloseButton(window);
            }
            SetIsHiddenCloseButton(window, true);
        }
        else if (!hideCloseButton && GetIsHiddenCloseButton(window)) {
            if (!window.IsLoaded) {
                window.Loaded -= ShowWhenLoadedDelegate;
            }
            else {
                ShowCloseButton(window);
            }
            SetIsHiddenCloseButton(window, false);
        }
    }

    #region Win32 imports

    private const int GWL_STYLE = -16;
    private const int WS_SYSMENU = 0x80000;
    [DllImport("user32.dll", SetLastError = true)]
    private static extern int GetWindowLong(IntPtr hWnd, int nIndex);
    [DllImport("user32.dll")]
    private static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);

    #endregion

    private static readonly RoutedEventHandler HideWhenLoadedDelegate = (sender, args) => {
        if (sender is Window == false) return;
        var w = (Window)sender;
        HideCloseButton(w);
        w.Loaded -= HideWhenLoadedDelegate;
    };

    private static readonly RoutedEventHandler ShowWhenLoadedDelegate = (sender, args) => {
        if (sender is Window == false) return;
        var w = (Window)sender;
        ShowCloseButton(w);
        w.Loaded -= ShowWhenLoadedDelegate;
    };

    private static void HideCloseButton(Window w) {
        var hwnd = new WindowInteropHelper(w).Handle;
        SetWindowLong(hwnd, GWL_STYLE, GetWindowLong(hwnd, GWL_STYLE) & ~WS_SYSMENU);
    }

    private static void ShowCloseButton(Window w) {
        var hwnd = new WindowInteropHelper(w).Handle;
        SetWindowLong(hwnd, GWL_STYLE, GetWindowLong(hwnd, GWL_STYLE) | WS_SYSMENU);
    }

    #endregion

    #region IsHiddenCloseButton (readonly attached property)

    private static readonly DependencyPropertyKey IsHiddenCloseButtonKey =
        DependencyProperty.RegisterAttachedReadOnly(
            "IsHiddenCloseButton",
            typeof (bool),
            OwnerType,
            new FrameworkPropertyMetadata(false));

    public static readonly DependencyProperty IsHiddenCloseButtonProperty =
        IsHiddenCloseButtonKey.DependencyProperty;

    [AttachedPropertyBrowsableForType(typeof(Window))]
    public static bool GetIsHiddenCloseButton(Window obj) {
        return (bool)obj.GetValue(IsHiddenCloseButtonProperty);
    }

    private static void SetIsHiddenCloseButton(Window obj, bool value) {
        obj.SetValue(IsHiddenCloseButtonKey, value);
    }

    #endregion

}

Then in XAML you just set it like this:

<Window 
    x:Class="WafClient.Presentation.Views.SampleWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:u="clr-namespace:WafClient.Presentation.Behaviors"
    ResizeMode="NoResize"
    u:WindowBehavior.HideCloseButton="True">
    ...
</Window>

So, pretty much here is your problem. The close button on the upper right of a window frame is not part of the WPF window, but it belongs to the part of the window frame that is controled by your OS. This means you will have to use Win32 interop to do it.

alternativly, you can use the noframe and either provide your own "frame" or have no frame at all.

I just add my implementation of Joe White's answer using Interactivity Behavior (you need to reference System.Windows.Interactivity).

code:

public class HideCloseButtonOnWindow : Behavior<Window>
{
    #region bunch of native methods

    private const int GWL_STYLE = -16;
    private const int WS_SYSMENU = 0x80000;

    [DllImport("user32.dll", SetLastError = true)]
    private static extern int GetWindowLong(IntPtr hWnd, int nIndex);

    [DllImport("user32.dll")]
    private static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);

    #endregion

    protected override void OnAttached()
    {
        base.OnAttached();
        AssociatedObject.Loaded += OnLoaded;
    }

    protected override void OnDetaching()
    {
        AssociatedObject.Loaded -= OnLoaded;
        base.OnDetaching();
    }

    private void OnLoaded(object sender, RoutedEventArgs e)
    {
        var hwnd = new WindowInteropHelper(AssociatedObject).Handle;
        SetWindowLong(hwnd, GWL_STYLE, GetWindowLong(hwnd, GWL_STYLE) & ~WS_SYSMENU);
    }
}

usage:

<Window x:Class="WpfApplication2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
        xmlns:w="clr-namespace:WpfApplication2">

    <i:Interaction.Behaviors>
        <w:HideCloseButtonOnWindow />
    </i:Interaction.Behaviors>

</Window>

As stated in other answers, you can use WindowStyle="None" to remove the Title Bar altogether.

And, as stated in the comments to those other answers, this prevents the window from being draggable so it is hard to move it from its initial position.

However, you can overcome this by adding a single line of code to the Constructor in the Window's Code Behind file:

MouseDown += delegate { DragMove(); };

Or, if you prefer Lambda Syntax:

MouseDown += (sender, args) => DragMove();

This makes the entire Window draggable. Any interactive controls present in the Window, such as Buttons, will still work as normal and won't act as drag-handles for the Window.

The following is about disabling the close and Maximize/Minimize buttons, it does not actually remove the buttons (but it does remove the menu items!). The buttons on the title bar are drawn in a disabled/grayed state. (I'm not quite ready to take over all the functionality myself ^^)

This is slightly different than Virgoss solution in that it removes the menu items (and the trailing separator, if needed) instead of just disabling them. It differs from Joe Whites solution as it does not disable the entire system menu and so, in my case, I can keep around the Minimize button and icon.

The follow code also supports disabling the Maximize/Minimize buttons as, unlike the Close button, removing the entries from the menu does not cause the system to render the buttons "disabled" even though removing the menu entries does disable the functionality of the buttons.

It works for me. YMMV.

    using System;
    using System.Collections.Generic;
    using System.Text;

    using System.Runtime.InteropServices;
    using Window = System.Windows.Window;
    using WindowInteropHelper = System.Windows.Interop.WindowInteropHelper;
    using Win32Exception = System.ComponentModel.Win32Exception;

    namespace Channelmatter.Guppy
    {

        public class WindowUtil
        {
            const int MF_BYCOMMAND = 0x0000;
            const int MF_BYPOSITION = 0x0400;

            const uint MFT_SEPARATOR = 0x0800;

            const uint MIIM_FTYPE = 0x0100;

            [DllImport("user32", SetLastError=true)]
            private static extern uint RemoveMenu(IntPtr hMenu, uint nPosition, uint wFlags);

            [DllImport("user32", SetLastError=true)]
            private static extern IntPtr GetSystemMenu(IntPtr hWnd, bool bRevert);

            [DllImport("user32", SetLastError=true)]
            private static extern int GetMenuItemCount(IntPtr hWnd);

            [StructLayout(LayoutKind.Sequential)]
            public struct MenuItemInfo {
                public uint   cbSize;
                public uint   fMask;
                public uint   fType;
                public uint   fState;
                public uint   wID;
                public IntPtr hSubMenu;
                public IntPtr hbmpChecked;
                public IntPtr hbmpUnchecked;
                public IntPtr dwItemData; // ULONG_PTR
                public IntPtr dwTypeData;
                public uint   cch;
                public IntPtr hbmpItem;
            };

            [DllImport("user32", SetLastError=true)]
            private static extern int GetMenuItemInfo(
                IntPtr hMenu, uint uItem,
                bool fByPosition, ref MenuItemInfo itemInfo);

            public enum MenuCommand : uint
            {
                SC_CLOSE = 0xF060,
                SC_MAXIMIZE = 0xF030,
            }

            public static void WithSystemMenu (Window win, Action<IntPtr> action) {
                var interop = new WindowInteropHelper(win);
                IntPtr hMenu = GetSystemMenu(interop.Handle, false);
                if (hMenu == IntPtr.Zero) {
                    throw new Win32Exception(Marshal.GetLastWin32Error(),
                        "Failed to get system menu");
                } else {
                    action(hMenu);
                }
            }

            // Removes the menu item for the specific command.
            // This will disable and gray the Close button and disable the
            // functionality behind the Maximize/Minimuze buttons, but it won't
            // gray out the Maximize/Minimize buttons. It will also not stop
            // the default Alt+F4 behavior.
            public static void RemoveMenuItem (Window win, MenuCommand command) {
                WithSystemMenu(win, (hMenu) => {
                    if (RemoveMenu(hMenu, (uint)command, MF_BYCOMMAND) == 0) {
                        throw new Win32Exception(Marshal.GetLastWin32Error(),
                            "Failed to remove menu item");
                    }
                });
            }

            public static bool RemoveTrailingSeparator (Window win) {
                bool result = false; // Func<...> not in .NET3 :-/
                WithSystemMenu(win, (hMenu) => {
                    result = RemoveTrailingSeparator(hMenu);
                });
                return result;
            }

            // Removes the final trailing separator of a menu if it exists.
            // Returns true if a separator is removed.
            public static bool RemoveTrailingSeparator (IntPtr hMenu) {
                int menuItemCount = GetMenuItemCount(hMenu);
                if (menuItemCount < 0) {
                    throw new Win32Exception(Marshal.GetLastWin32Error(),
                        "Failed to get menu item count");
                }
                if (menuItemCount == 0) {
                    return false;
                } else {
                    uint index = (uint)(menuItemCount - 1);
                    MenuItemInfo itemInfo = new MenuItemInfo {
                        cbSize = (uint)Marshal.SizeOf(typeof(MenuItemInfo)),
                        fMask = MIIM_FTYPE,
                    };

                    if (GetMenuItemInfo(hMenu, index, true, ref itemInfo) == 0) {
                        throw new Win32Exception(Marshal.GetLastWin32Error(),
                            "Failed to get menu item info");
                    }

                    if (itemInfo.fType == MFT_SEPARATOR) {
                        if (RemoveMenu(hMenu, index, MF_BYPOSITION) == 0) {
                            throw new Win32Exception(Marshal.GetLastWin32Error(),
                                "Failed to remove menu item");
                        }
                        return true;
                    } else {
                        return false;
                    }
                }
            }

            private const int GWL_STYLE = -16;

            [Flags]
            public enum WindowStyle : int
            {
                WS_MINIMIZEBOX = 0x00020000,
                WS_MAXIMIZEBOX = 0x00010000,
            }

            // Don't use this version for dealing with pointers
            [DllImport("user32", SetLastError=true)]
            private static extern int SetWindowLong (IntPtr hWnd, int nIndex, int dwNewLong);

            // Don't use this version for dealing with pointers
            [DllImport("user32", SetLastError=true)]
            private static extern int GetWindowLong (IntPtr hWnd, int nIndex);

            public static int AlterWindowStyle (Window win,
                WindowStyle orFlags, WindowStyle andNotFlags) 
            {
                var interop = new WindowInteropHelper(win);

                int prevStyle = GetWindowLong(interop.Handle, GWL_STYLE);
                if (prevStyle == 0) {
                    throw new Win32Exception(Marshal.GetLastWin32Error(),
                        "Failed to get window style");
                }

                int newStyle = (prevStyle | (int)orFlags) & ~((int)andNotFlags);
                if (SetWindowLong(interop.Handle, GWL_STYLE, newStyle) == 0) {
                    throw new Win32Exception(Marshal.GetLastWin32Error(),
                        "Failed to set window style");
                }
                return prevStyle;
            }

            public static int DisableMaximizeButton (Window win) {
                return AlterWindowStyle(win, 0, WindowStyle.WS_MAXIMIZEBOX);
            }
        }
    }

Usage: This must be done AFTER the source is initialized. A good place is to use the SourceInitialized event of the Window:

Window win = ...; /* the Window :-) */
WindowUtil.DisableMaximizeButton(win);
WindowUtil.RemoveMenuItem(win, WindowUtil.MenuCommand.SC_MAXIMIZE);
WindowUtil.RemoveMenuItem(win, WindowUtil.MenuCommand.SC_CLOSE);
while (WindowUtil.RemoveTrailingSeparator(win)) 
{
   //do it here
}

To disable the Alt+F4 functionality the easy method is just to wire up the Canceling event and use set a flag for when you really do want to close the window.

After much searching for the answer to this, I worked out this simple solution that I will share here in hopes it helps others.

I set WindowStyle=0x10000000.

This sets the WS_VISIBLE (0x10000000) and WS_OVERLAPPED (0x0) values for Window Style. "Overlapped" is the necessary value to show the title bar and window border. By removing the WS_MINIMIZEBOX (0x20000), WS_MAXIMIZEBOX (0x10000), and WS_SYSMENU (0x80000) values from my style value, all the buttons from the title bar were removed, including the Close button.

XAML Code

<Button Command="Open" Content="_Open">
    <Button.Style>
        <Style TargetType="Button">
            <Style.Triggers>
                <Trigger Property="IsEnabled" Value="False">
                    <Setter Property="Visibility" Value="Collapsed" />
                </Trigger>
            </Style.Triggers>
        </Style>
     </Button.Style>
</Button>

should work

Edit- for your instant this Thread shows how that can be done but I don't think Window has a property to get what you want without losing the normal title bar.

Edit 2 This Thread shows a way for it to be done, but you must apply your own style to the system menu and it shows a way how you can do that.

To disable close button you should add the following code to your Window class (the code was taken from here, edited and reformatted a bit):

protected override void OnSourceInitialized(EventArgs e)
{
    base.OnSourceInitialized(e);

    HwndSource hwndSource = PresentationSource.FromVisual(this) as HwndSource;

    if (hwndSource != null)
    {
        hwndSource.AddHook(HwndSourceHook);
    }

}

private bool allowClosing = false;

[DllImport("user32.dll")]
private static extern IntPtr GetSystemMenu(IntPtr hWnd, bool bRevert);
[DllImport("user32.dll")]
private static extern bool EnableMenuItem(IntPtr hMenu, uint uIDEnableItem, uint uEnable);

private const uint MF_BYCOMMAND = 0x00000000;
private const uint MF_GRAYED = 0x00000001;

private const uint SC_CLOSE = 0xF060;

private const int WM_SHOWWINDOW = 0x00000018;
private const int WM_CLOSE = 0x10;

private IntPtr HwndSourceHook(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
{
    switch (msg)
    {
        case WM_SHOWWINDOW:
            {
                IntPtr hMenu = GetSystemMenu(hwnd, false);
                if (hMenu != IntPtr.Zero)
                {
                    EnableMenuItem(hMenu, SC_CLOSE, MF_BYCOMMAND | MF_GRAYED);
                }
            }
            break;
        case WM_CLOSE:
            if (!allowClosing)
            {
                handled = true;
            }
            break;
    }
    return IntPtr.Zero;
}

This code also disables close item in System menu and disallows closing the dialog using Alt+F4.

You will probably want to close the window programmatically. Just calling Close() will not work. Do something like this:

allowClosing = true;
Close();

Let the user "close" the window but really just hide it.

In the window's OnClosing event, hide the window if already visible:

    If Me.Visibility = Windows.Visibility.Visible Then
        Me.Visibility = Windows.Visibility.Hidden
        e.Cancel = True
    End If

Each time the Background thread is to be executed, re-show background UI window:

    w.Visibility = Windows.Visibility.Visible
    w.Show()

When terminating execution of program, make sure all windows are/can-be closed:

Private Sub CloseAll()
    If w IsNot Nothing Then
        w.Visibility = Windows.Visibility.Collapsed ' Tell OnClosing to really close
        w.Close()
    End If
End Sub

goto window properties set

window style = none;

u wont get close buttons...

Use WindowStyle="SingleBorderWindow" , this will hide max and min button from WPF Window.

If the need is only to prohibit the user from closing the window, this is a simple solution.

XAML code: IsCloseButtonEnabled="False"

It's block the button.

I was trying Viachaslau's answer since I like the idea of not removing the button but disabling it, but for some reason it did not always work: the close button was still enabled but no errors whatsoever.

This on the other hand always worked (error checking omitted):

[DllImport( "user32.dll" )]
private static extern IntPtr GetSystemMenu( IntPtr hWnd, bool bRevert );
[DllImport( "user32.dll" )]
private static extern bool EnableMenuItem( IntPtr hMenu, uint uIDEnableItem, uint uEnable );

private const uint MF_BYCOMMAND = 0x00000000;
private const uint MF_GRAYED = 0x00000001;
private const uint SC_CLOSE = 0xF060;
private const int WM_SHOWWINDOW = 0x00000018;

protected override void OnSourceInitialized( EventArgs e )
{
  base.OnSourceInitialized( e );
  var hWnd = new WindowInteropHelper( this );
  var sysMenu = GetSystemMenu( hWnd.Handle, false );
  EnableMenuItem( sysMenu, SC_CLOSE, MF_BYCOMMAND | MF_GRAYED );
}

Use this, modified from https://stephenhaunts.com/2014/09/25/remove-the-close-button-from-a-wpf-window :

using System;
using System.Runtime.InteropServices;
using System.Windows;
using System.Windows.Input;
using System.Windows.Interop;
using System.Windows.Media;

namespace Whatever
{
    public partial class MainMenu : Window
    {
        private const int GWL_STYLE = -16;
        private const int WS_SYSMENU = 0x00080000;

        [DllImport("user32.dll", SetLastError = true)]
        private static extern int GetWindowLongPtr(IntPtr hWnd, int nIndex);

        [DllImport("user32.dll")]
        private static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);

        public MainMenu()
        {
             InitializeComponent();
             this.Loaded += new RoutedEventHandler(Window_Loaded);
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            var hwnd = new WindowInteropHelper(this).Handle;
            SetWindowLongPtr(hwnd, GWL_STYLE, GetWindowLongPtr(hwnd, GWL_STYLE) & ~WS_SYSMENU);
        }  

    }
}

The property to set is => WindowStyle="None"

<Window x:Class="mdaframework.MainWindow"
            xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
            Title="Start" Height="350" Width="525" ResizeMode="NoResize"  WindowStartupLocation="CenterScreen" WindowStyle="None">

I very much like this answer which uses attached properties to mediate the behavior. However, I found that answer's implementation overly complicated, and it also doesn't address the secondary goal of preventing the window from being closed even with Alt+F4. So I offer this alternative:

enum CloseButtonVisibility
{
    Visible,
    Hidden,
    CloseDisabled,
}

static class WindowEx
{
    private static readonly CancelEventHandler _cancelCloseHandler = (sender, e) => e.Cancel = true;

    public static readonly DependencyProperty CloseButtonVisibilityProperty =
        DependencyProperty.RegisterAttached(
            "CloseButtonVisibility",
            typeof(CloseButtonVisibility),
            typeof(WindowEx),
            new FrameworkPropertyMetadata(CloseButtonVisibility.Visible, new PropertyChangedCallback(_OnCloseButtonChanged)));

    [AttachedPropertyBrowsableForType(typeof(Window))]
    public static CloseButtonVisibility GetCloseButtonVisibility(Window obj)
    {
        return (CloseButtonVisibility)obj.GetValue(CloseButtonVisibilityProperty);
    }

    [AttachedPropertyBrowsableForType(typeof(Window))]
    public static void SetCloseButtonVisibility(Window obj, CloseButtonVisibility value)
    {
        obj.SetValue(CloseButtonVisibilityProperty, value);
    }

    private static void _OnCloseButtonChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (!(d is Window window))
        {
            return;
        }

        if (e.OldValue is CloseButtonVisibility oldVisibility)
        {
            if (oldVisibility == CloseButtonVisibility.CloseDisabled)
            {
                window.Closing -= _cancelCloseHandler;
            }
        }

        if (e.NewValue is CloseButtonVisibility newVisibility)
        {
            if (newVisibility == CloseButtonVisibility.CloseDisabled)
            {
                window.Closing += _cancelCloseHandler;
            }

            if (!window.IsLoaded)
            {
                // NOTE: if the property is set multiple times before the window is loaded,
                // the window will wind up with multiple event handlers. But they will all
                // set the same value, so this is fine from a functionality point of view.
                //
                // The handler is never unsubscribed, so there is some nominal overhead there.
                // But it would be incredibly unusual for this to be set more than once
                // before the window is loaded, and even a handful of delegate instances
                // being around that are no longer needed is not really a big deal.
                window.Loaded += _ApplyCloseButtonVisibility;
            }
            else
            {
                _SetVisibility(window, newVisibility);
            }
        }
    }

    #region Win32 imports

    private const int GWL_STYLE = -16;
    private const int WS_SYSMENU = 0x80000;
    [DllImport("user32.dll", SetLastError = true)]
    private static extern int GetWindowLong(IntPtr hWnd, int nIndex);
    [DllImport("user32.dll")]
    private static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);

    #endregion

    private static void _ApplyCloseButtonVisibility(object sender, RoutedEventArgs e)
    {
        Window window = (Window)sender;
        CloseButtonVisibility visibility = GetCloseButtonVisibility(window);

        _SetVisibility(window, visibility);
    }

    private static void _SetVisibility(Window window, CloseButtonVisibility visibility)
    {
        var hwnd = new WindowInteropHelper(window).Handle;

        if (visibility == CloseButtonVisibility.Visible)
        {
            SetWindowLong(hwnd, GWL_STYLE, GetWindowLong(hwnd, GWL_STYLE) | WS_SYSMENU);
        }
        else
        {
            SetWindowLong(hwnd, GWL_STYLE, GetWindowLong(hwnd, GWL_STYLE) & ~WS_SYSMENU);
        }
    }
}

This provides three states to choose from:

1. Visible
2. Hidden, but user can still close using Alt+F4
3. Hidden, and closing is disabled completely

Note that by default, a window that is never closed will prevent a WPF program's process from terminating. So if you choose to use the CloseButtonVisibility.CloseDisabled value, you will need to either customize the Application.Run() behavior, or re-enable closing of the window before exiting. E.g. in your main window, you might have something like this:

protected override void OnClosed(EventArgs e)
{
    WindowEx.SetCloseButtonVisibility(this.toolWindow.Value, CloseButtonVisibility.Hidden);
    this.toolWindow.Value.Close();

    base.OnClosed(e);
}

where toolWindow is the Window reference for the window with the close button disabled.

The above assumes that the window is normally just hidden and shown as needed during the normal UI activity. Of course, you can also choose to close the window explicitly at any time, but the same technique — setting the option to not disable closing, and then explicitly closing the window — would still apply.

Set WindowStyle property to None which will hide the control box along with the title bar. No need to kernal calls.

This won't get rid of the close button, but it will stop someone closing the window.

Put this in your code behind file:

protected override void OnClosing(CancelEventArgs e)
{
   base.OnClosing(e);
   e.Cancel = true;
}