如何使用ReactiveUI正确取消ViewModel去激活上的任务？

using System;
using System.Reactive;
using System.Reactive.Disposables;
using System.Reactive.Linq;
using System.Threading;
using ReactiveUI;

public class MyViewModel : ReactiveObject, ISupportsActivation
{
    private CancellationTokenSource _cancellationTokenSource;

    public ViewModelActivator Activator { get; }

    public MyViewModel()
    {
        Activator = new ViewModelActivator();

        this.WhenActivated(disposables =>
        {
            _cancellationTokenSource = new CancellationTokenSource();
            var cancellationToken = _cancellationTokenSource.Token;

            // 在需要执行任务的方法中使用cancellationToken

            // 示例：执行一个耗时操作
            Observable.Start(async () =>
            {
                // 模拟耗时操作
                await Task.Delay(TimeSpan.FromSeconds(5), cancellationToken);

                // 检查是否需要取消任务
                cancellationToken.ThrowIfCancellationRequested();

                // 继续执行任务
                await Task.Delay(TimeSpan.FromSeconds(3), cancellationToken);

                // 检查是否需要取消任务
                cancellationToken.ThrowIfCancellationRequested();

                // 继续执行任务
                // ...
            })
            .Subscribe()
            .DisposeWith(disposables);

            // 在Deactivate方法中取消任务
            this.WhenDeactivated(() =>
            {
                _cancellationTokenSource?.Cancel();
                _cancellationTokenSource?.Dispose();
                _cancellationTokenSource = null;
            });
        });
    }
}