WPF/C#：程序关闭的三种模式

<Window x:Class="ApplicationShutdown.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:ApplicationShutdown"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525" Loaded="MainWindow_Loaded">
    <DockPanel>
        <StackPanel DockPanel.Dock="Top" Orientation="Horizontal">
            <Label HorizontalAlignment="Left">Shutdown Mode:</Label>
            <ComboBox HorizontalAlignment="Left" Name="shutdownModeListBox" />
        </StackPanel>
        <StackPanel DockPanel.Dock="Top" Orientation="Horizontal">
            <Label HorizontalAlignment="Left">Application Exit Code (for explicit shutdown):</Label>
            <TextBox HorizontalAlignment="Left" Name="appExitCodeTextBox">0</TextBox>
        </StackPanel>
        <Button DockPanel.Dock="Top" Click="newWindowButton_Click">New Window</Button>
        <Button DockPanel.Dock="Top" Click="explicitShutdownButton_Click">Shutdown Explicitly (Passing Exit Code)</Button>
        <Canvas />
    </DockPanel>
</Window>

using System;
using System.Windows;
using System.Windows.Controls;
namespace ApplicationShutdown
{
    /// <summary>
    ///     Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
        private void MainWindow_Loaded(object sender, RoutedEventArgs e)
        {
            shutdownModeListBox.Items.Add("OnLastWindowClose");
            shutdownModeListBox.Items.Add("OnExplicitShutdown");
            shutdownModeListBox.Items.Add("OnMainWindowClose");
            shutdownModeListBox.SelectedValue = "OnLastWindowClose";
            shutdownModeListBox.SelectionChanged +=
                shutdownModeListBox_SelectionChanged;
            Application.Current.ShutdownMode = ShutdownMode.OnLastWindowClose;
        }
        private void shutdownModeListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            Application.Current.ShutdownMode =
                (ShutdownMode) Enum.Parse(typeof (ShutdownMode), shutdownModeListBox.SelectedValue.ToString());
        }
        private void newWindowButton_Click(object sender, RoutedEventArgs e)
        {
            (new ChildWindow()).Show();
        }
        private void explicitShutdownButton_Click(object sender, RoutedEventArgs e)
        {
            var exitCode = 0;
            int.TryParse(appExitCodeTextBox.Text, out exitCode);
            Application.Current.Shutdown(exitCode);
        }
    }
}

<Window x:Class="ApplicationShutdown.ChildWindow"
        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:ApplicationShutdown"
        mc:Ignorable="d"
        Title="ChildWindow" Height="300" 
        Width="300"     
        Closing="ChildWindow_Closing" 
        Closed="ChildWindow_Closed">
    <Grid/>
</Window>

using System;
using System.ComponentModel;
using System.Windows;
namespace ApplicationShutdown
{
    /// <summary>
    ///     Interaction logic for ChildWindow.xaml
    /// </summary>
    public partial class ChildWindow : Window
    {
        public ChildWindow()
        {
            InitializeComponent();
        }
        private void ChildWindow_Closing(object sender, CancelEventArgs e)
        {
            Console.WriteLine(@"Closing");
            var result = MessageBox.Show("Allow Shutdown?", "Application Shutdown Sample",
                MessageBoxButton.YesNo,
                MessageBoxImage.Question);
            e.Cancel = (result == MessageBoxResult.No);
        }
        private void ChildWindow_Closed(object sender, EventArgs e)
        {
            Console.WriteLine(@"Closed");
        }
    }
}