c#-在ReactiveUI ViewModel中取消异步任务(ReactiveObject)

我目前正在使用ReactiveUI(5.5.1)进行实验,并创建了一个ViewModel(ReactiveObject的子类),它可以自动完成位置搜索(改编自mikebluestein/ReactiveUIDemo on github).每次查询文本更改时,都会调用REST服务,该服务返回所提交查询的匹配位置.

问题：正如您在下面的代码中看到的那样,可以取消DoSearchAsync(string query,CancellationToken cancelestToken),但是,我不确定如何(以及在​​代码中的位置)实际取消任何搜索-因此使用CancellationToken.None atm.在这种特定用例中取消请求似乎是一个过大的杀手,但我想知道无论如何在这种reactUI / async-Task场景中如何启用取消.

码：

public class ReactiveLocationSearchViewModel : ReactiveObject {

readonly ReactiveCommand searchCommand = new ReactiveCommand();

public ReactiveCommand SearchCommand { get { return searchCommand; } }

string query;

public string Query
{
    get { return query; }
    set { this.RaiseAndSetIfChanged(ref query, value); }
}

public ReactiveList<Location> ReactiveData { get; protected set; }

public ReactiveLocationSearchViewModel()
{
    ReactiveData = new ReactiveList<Location>();
    var results = searchCommand.RegisterAsyncTask<List<Location>>(async _ => await DoSearchAsync(query, CancellationToken.None));

    this.ObservableForProperty<ReactiveLocationSearchViewModel, string>("Query")
        .Throttle(new TimeSpan(700))
        .Select(x => x.Value).DistinctUntilChanged()
        .Where(x => !String.IsNullOrWhiteSpace(x))
        .Subscribe(searchCommand.Execute);

    results.Subscribe(list =>
    {
        ReactiveData.Clear();
        ReactiveData.AddRange(list);
    });
}

private async Task<List<Location>> DoSearchAsync(string query, CancellationToken cancellationToken)
{
    // create default empty list
    var locations = new List<Location>();

    // only search if query is not empty
    if (!string.IsNullOrEmpty(query))
    {
        ILocationService service = ServiceContainer.Resolve<ILocationService>();
        locations = await service.GetLocationsAsync(query, cancellationToken);
    }

    return locations;
}

}

解决方法:

RxUI 5.x没有内置的功能,但是很容易伪造：

var results = searchCommand.RegisterAsync<List<Location>>(
    _ => Observable.StartAsync(ct => DoSearchAsync(query, ct)));

在RxUI v6中,这是内置的：

searchCommand = ReactiveCommand.CreateAsyncTask(
    (_, ct) => DoSearchAsync(query, ct));

标签：cancellation,reactiveui,c,mvvm
来源： https://codeday.me/bug/20191121/2053328.html