やりたいこと

USBデバイスが抜き差しされたタイミングで、ViewModelのコマンドを実行する。

実装

USB抜き差し時にコマンドを実行するビヘイビアを作成する。

ビヘイビア

using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Interop;

namespace Sample {
    public class DeviceChangeBehavior {
        private static readonly uint WM_DEVICECHANGE = 0x0219;

        public static DependencyProperty CommandProperty
            = DependencyProperty.RegisterAttached(
                "Command",
                typeof(ICommand),
                typeof(DeviceChangeBehavior),
                new PropertyMetadata(Command_PropertyChanged)
            );

        public static void SetCommand(FrameworkElement element, ICommand value)
            => element.SetValue(CommandProperty, value);

        public static ICommand GetCommand(FrameworkElement element)
            => (ICommand)element.GetValue(CommandProperty);

        private static Dictionary<FrameworkElement, ICommand> _commands
            = new Dictionary<FrameworkElement, ICommand>();

        private static void Command_PropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) {
            var element = d as FrameworkElement;
            if (element == null) return;

            if (e.NewValue != null) {
                element.Loaded += FrameworkElement_Loaded;
                _commands.Add(control, e.NewValue as ICommand);
            } else {
                element.Loaded -= FrameworkElement_Loaded;
                var handle = ((HwndSource)HwndSource.FromVisual(element)).Handle;
                var source = HwndSource.FromHwnd(handle);
                source.RemoveHook(WndProc);
                _commands.Remove(element);
            }
        }

        private static void FrameworkElement_Loaded(object sender, RoutedEventArgs e) {
            var element = sender as FrameworkElement;
            if (element == null) return;

            //ロード完了後でないとハンドラを登録できない
            var handle = ((HwndSource)HwndSource.FromVisual(element)).Handle;
            var source = HwndSource.FromHwnd(handle);

            source.AddHook(WndProc);
        }

        private static IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled) {
            if (msg != WM_DEVICECHANGE)
                return IntPtr.Zero;

            _commands
                .Select(x => new { ((HwndSource)HwndSource.FromVisual(x.Key))?.Handle, Command = x.Value })
                .Where(x => x.Handle == hwnd && x.Command.CanExecute(null))
                .ForEach(x => x.Command.Execute(null));

            return IntPtr.Zero;
        }
    }
}

使い方

XAML

<Window x:Class="Sample.MainView"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:Sample"
        local:DeviceChangeBehavior.Command="{Binding XXXCommand}"
        Title="MainView" Height="300" Width="300">
    <Grid>
        <TextBox />
    </Grid>
</Window>

Window以外にも指定できるが、ルート要素に指定するのが無難。