WPFでMVVMを学ぶ：基本からMVVM Toolkitでの簡潔な実装まで

namespace WpfTest.Model;

public class Person
{
	public string? Name { get; set; }
	public string? Email { get; set; }
	public int Age { get; set; }
}

public class UserVM : INotifyPropertyChanged
{
    // プロパティの変更を通知するイベント
	public event PropertyChangedEventHandler? PropertyChanged;

    // イベントを呼び出すメソッド
	private void OnPropertyChanged(string propertyName)
	{
		PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
	}
}

// イベントなどは省略
public class UserVM : INotifyPropertyChanged
{
    // （略）イベント定義

    // テキストボックスに入力されたユーザー名用プロパティ
	private string? userName;
	public string? UserName
	{
		get { return userName; }
		set
		{
			userName = value;
			OnPropertyChanged(nameof(UserName));
		}
	}

    // ユーザー情報用プロパティ
	private Person person = default!;
	public Person Person
	{
		get { return person; }
		set
		{
			person = value;
			OnPropertyChanged(nameof(Person));
		}
	}

}

public partial class Main : Window
{
	public Main()
	{
		InitializeComponent();
        // DIとしてVMを受け取りDataContextにセットする
		DataContext = App.Current.Services.GetService<UserVM>();
	}
}

<Window x:Class="WpfTest.View.Main"
　　　　　（略）
        xmlns:local="clr-namespace:WpfTest.View"
        xmlns:vm="clr-namespace:WpfTest.ViewModel"
        mc:Ignorable="d"
        d:DataContext="{d:DesignInstance vm:UserVM}"
        Title="Main" Height="450" Width="800">

    <Grid Width="400">
        <Grid.RowDefinitions>
          （略）
        </Grid.RowDefinitions>

        <Grid Grid.Row="0">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="7*"/>
                <ColumnDefinition Width="3*"/>
            </Grid.ColumnDefinitions>
            <TextBox Text="{Binding UserName}" Grid.Column="0" Style="{StaticResource FormInput}"/>
            <Button Grid.Column="1" Style="{StaticResource Common}" Content="検索"/>
        </Grid>

        <Grid Grid.Row="1">
            <GroupBox Header="結果" Style="{StaticResource GroupBox_Common}">
                <StackPanel>
                    // ResultTextもUserNameなどと同様にViewModelにプロパティを作成しておく
                    <TextBlock Text="{Binding ResultText}" />
                    <TextBlock Text="{Binding Person.Name}" />
                    <TextBlock Text="{Binding Person.Email}"/>
                    <TextBlock Text="{Binding Person.Age}" />
                </StackPanel>
            </GroupBox>
        </Grid>
    </Grid>
</Window>

public class UserCommand : ICommand
{
	public UserVM UserVM { get; set; }

	public UserCommand(UserVM vm) => UserVM = vm;

	public event EventHandler? CanExecuteChanged
	{
		add { CommandManager.RequerySuggested += value; }
		remove { CommandManager.RequerySuggested -= value; }
	}

	public bool CanExecute(object? parameter) => true;

	public void Execute(object? parameter)
	{
        // ViewModelに以下のメソッドを作成
		UserVM.GetPersonInfo(parameter as string ?? "");
	}
}

public class UserVM : INotifyPropertyChanged
{

	private readonly IPersonInfo pi;

	public UserCommand UserCommand { get; set; }

	public UserVM(IPersonInfo personInfo)
	{
		UserCommand = new UserCommand(this);
		pi = personInfo;
	}

	public void GetPersonInfo(string name)
	{
		Person = pi.Get(name);
		if (string.IsNullOrEmpty(person.Name))
		{
			ResultText = "該当なし";
		}
		else
		{
			ResultText = "1件";
		}
	}

}

public class PersonInfo : IPersonInfo
{

	private List<Person> _people = new List<Person>()
	{
		new Person{Name = "Test1",Age=10,Email="aaa.com"},
		new Person{Name = "Test2",Age=20,Email="bbb.com"},
		new Person{Name = "Test3",Age=30,Email="ccc.com"},
	};

	public Person Get(string name)
	{
		return _people.Find(n => n.Name == name) ?? new();
	}
}

<Button Grid.Column="1" Command="{Binding UserCommand}" CommandParameter="{Binding UserName}" ・・・/>

internal partial class ToolkitVM : ObservableObject
{
	private readonly IPersonInfo _pi;
	public ToolkitVM(IPersonInfo personInfo)
	{
		_pi = personInfo;
	}

	[ObservableProperty]
	private string? _userName;
	[ObservableProperty]
	private string? _resultText;

	[ObservableProperty]
	private Person _person = default!;

	[RelayCommand]
	private void GetPersonInfo(string name)
	{
		Person = _pi.Get(name);
		if (string.IsNullOrEmpty(Person.Name))
		{
			ResultText = "該当なし";
		}
		else
		{
			ResultText = "1件";
		}
	}

}

// Microsoft.Extensions.DependencyInjectionをインストール

namespace WpfTest;

/// <summary>
/// Interaction logic for App.xaml
/// </summary>
public partial class App : Application
{
	public App()
	{
		Services = ConfigureServices();
		this.InitializeComponent();
	}
	public new static App Current => (App)Application.Current;

	public IServiceProvider Services { get; } = default!;

	private static IServiceProvider ConfigureServices()
	{
		var services = new ServiceCollection();
		services.AddSingleton<IPersonInfo, PersonInfo>();
		services.AddTransient<UserVM>();
		services.AddTransient<ToolkitVM>();

		return services.BuildServiceProvider();
	}

}