namespace System.ComponentModel
{
    // Notifies clients that a property value has changed.
    public interface INotifyPropertyChanged
    {
        // Occurs when a property value changes.
        event PropertyChangedEventHandler? PropertyChanged;
    }
}

public class NativeViewModel : INotifyPropertyChanged
{
    private string _name;

    public string Name
    {
        get => _name;
        set
        {
            if (_name != value)
            {
                _name = value;
                OnPropertyChanged();
            }
        }
    }
    protected virtual void OnPropertyChanged([CallerMemberName] string? propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

<StackPanel>
    <TextBox Text="{Binding Name}" />
</StackPanel>

#nullable enable

using System.ComponentModel;
using System.Windows.Markup;

namespace System.Windows.Input
{
    //
    // 摘要:
    //     Defines a command.
    [TypeConverter("System.Windows.Input.CommandConverter, PresentationFramework, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, Custom=null")]
    [ValueSerializer("System.Windows.Input.CommandValueSerializer, PresentationFramework, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, Custom=null")]
    public interface ICommand
    {
        //
        // 摘要:
        //     Occurs when changes occur that affect whether or not the command should execute.
        event EventHandler? CanExecuteChanged;

        //
        // 摘要:
        //     Defines the method that determines whether the command can execute in its current
        //     state.
        //
        // 參數(shù):
        //   parameter:
        //     Data used by the command. If the command does not require data to be passed,
        //     this object can be set to null.
        //
        // 返回結(jié)果:
        //     true if this command can be executed; otherwise, false.
        bool CanExecute(object? parameter);
        //
        // 摘要:
        //     Defines the method to be called when the command is invoked.
        //
        // 參數(shù):
        //   parameter:
        //     Data used by the command. If the command does not require data to be passed,
        //     this object can be set to null.
        void Execute(object? parameter);
    }
}

public class NativeViewModel
{
    public ICommand GreetCommand { get; }

    public NativeViewModel()
    {
        // 使用自定義的 RelayCommand 需要自己實(shí)現(xiàn)
        GreetCommand = new RelayCommand();
    }
}

// 需要實(shí)現(xiàn)的簡(jiǎn)單命令類
public class RelayCommand : ICommand
{
    // 略
}

<StackPanel>
    <Button Content="Say Hello" Command="{Binding GreetCommand}" />
</StackPanel>

using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;

// 3. 使用 [ObservableObject] 特性或繼承 ObservableObject
[ObservableObject]
public partial class ToolkitViewModel
{
    // 4. 使用 [ObservableProperty] 標(biāo)記字段，自動(dòng)生成名為 "Name" 的屬性
    [ObservableProperty]
    [NotifyCanExecuteChangedFor(nameof(GreetCommand))] // 當(dāng) Name 改變時(shí)，通知 GreetCommand 重新驗(yàn)證
    private string _name;

    [ObservableProperty]
    private string _greeting;

    // 5. 使用 [RelayCommand] 自動(dòng)生成名為 GreetCommand 的 ICommand 屬性
    [RelayCommand(CanExecute = nameof(CanGreet))]
    private void Greet()
    {
        Greeting = $"Hello from Toolkit, {Name}!";
    }

    private bool CanGreet() => !string.IsNullOrWhiteSpace(Name);
}

using ReactiveUI;
using System.Reactive.Linq;

// 6. 繼承 ReactiveObject
public class ReactiveViewModel : ReactiveObject
{
    // 7. 使用 [Reactive] 特性或 WhenAnyValue
    private string _name;
    public string Name
    {
        get => _name;
        set => this.RaiseAndSetIfChanged(ref _name, value);
    }

    private readonly ObservableAsPropertyHelper<string> _greeting;
    public string Greeting => _greeting.Value;

    // 8. 使用 ReactiveCommand 創(chuàng)建命令
    public ReactiveCommand<Unit, Unit> GreetCommand { get; }

    public ReactiveViewModel()
    {
        // 判斷命令何時(shí)可執(zhí)行：當(dāng) Name 不為空時(shí)
        var canGreet = this.WhenAnyValue(x => x.Name, name => !string.IsNullOrWhiteSpace(name));

        // 創(chuàng)建命令
        GreetCommand = ReactiveCommand.CreateFromTask(
            execute: async () => { /* 可以執(zhí)行異步操作 */ return $"Hello from ReactiveUI, {Name}!"; },
            canExecute: canGreet // 綁定可執(zhí)行條件
        );

        // 9. 將命令的執(zhí)行結(jié)果（一個(gè)IObservable<string>）訂閱到 Greeting 屬性
        _greeting = GreetCommand.ToProperty(this, x => x.Greeting, initialValue: "Waiting...");

        // 另一種更直接的寫法（不通過命令結(jié)果）:
        // GreetCommand = ReactiveCommand.Create(() => { Greeting = $"Hello from ReactiveUI, {Name}!"; }, canGreet);
        // 但上面那種方式展示了將 IObservable 流轉(zhuǎn)換為屬性的強(qiáng)大能力。
    }
}