Problem running example from System.Windows.Application.Windows property documentation

Question

In the Windows Desktop 6.0 documentation at this link (https://learn.microsoft.com/en-us/dotnet/api/system.windows.application.windows?view=windowsdesktop-6.0) there is an example showing how to use the Windows property. I coded a WPF (.NET 6) application with that code, built it, and ran it. However, if I select the menu item File > New Window, it displays the InvalidCastException shown in the attachment. The menuItem is being created as a WindowMenuItem not a System.Windows.Controls.MenuItem so I don't know why I'm getting that exception. AppWindows is the name of my namespace. What am I doing wrong?

Answer 1

Hi @Nicholas Piazza , Welcome to Microsoft Q&A.

For event handler for menuitem_click, please do not add it as click event in Xaml.

They are not the same, you should write newwindowmenuitem_click, don't confuse it with menuitem_click.

That's why you got this error.

you could try the following code to get what you wanted.

Xaml:

<Window x:Class="WpfApp1.MainWindow"  
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"  
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"  
        xmlns:local="clr-namespace:WpfApp1"  
        mc:Ignorable="d"  
         Title="CSharp" Height="300" Width="300" Activated="MainWindow_Activated">  
    <StackPanel>  
        <Menu>  
            <MenuItem Header="_File">  
                <MenuItem Name="newWindowMenuItem" Click="newWindowMenuItem_Click" Header="_New Window"></MenuItem>  
                <Separator></Separator>  
                <MenuItem Name="exitMenuItem" Click="exitMenuItem_Click" Header="E_xit"></MenuItem>  
            </MenuItem>  
            <MenuItem Name="windowMenuItem" Header="_Window">  
            </MenuItem>  
        </Menu>  
        <Canvas></Canvas>  
    </StackPanel>  
</Window>  

Code:

using System;  
using System.Windows;  
using System.Windows.Controls;  
  
namespace WpfApp1  
{  
	/// <summary>  
	/// Interaction logic for MainWindow.xaml  
	/// </summary>  
	public partial class MainWindow : Window  
	{  
		public MainWindow()  
		{  
			InitializeComponent();  
		}  
		//Add a current window counter  
  
		private int newWindowCount = 0;  
  
		//When the main window is active, add menu items to the submenus of windowMenuItem,  
		//each menu item displays the title of the window  
		void MainWindow_Activated(object sender, EventArgs e)  
		{  
			this.windowMenuItem.Items.Clear();  
			int windowCount = 0;  
			foreach (Window window in Application.Current.Windows)  
			{  
				++windowCount;  
				MenuItem menuItem = new MenuItem();  
				menuItem.Tag = window;  
				menuItem.Header = window.Title;  
				menuItem.Click += new RoutedEventHandler(menuItem_Click);  
				this.windowMenuItem.Items.Add(menuItem);  
			}  
		}  
  
		//Activate the window when the menu item is clicked  
		private void menuItem_Click(object sender, RoutedEventArgs e)  
		{  
			MenuItem menuItem = (MenuItem)sender;  
			((Window)menuItem.Tag).Activate();  
		}  
  
		//When the New button is clicked,  
		//a new window is created and the current window content is set as the window title  
		private void newWindowMenuItem_Click(object sender, RoutedEventArgs e)  
		{  
			Window win1 = new Window();  
			win1.Height = 300;  
			win1.Width = 300;  
			++newWindowCount;  
			win1.Content = win1.Title = "This is the" + newWindowCount.ToString().PadLeft(2, '0') + "mchild window.";  
			win1.Show();  
		}  
  
		private void exitMenuItem_Click(object sender, RoutedEventArgs e)  
		{  
			Application.Current.MainWindow.Close();  
		}  
	}  
}  

Best Regards,
Jiale

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