在reactiveuiviewmodel (ReactiveObject)中取消异步任务

本文关键字：取消 异步 任务 reactiveuiviewmodel ReactiveObject | 更新日期: 2023-09-27 18:07:38

我目前正在试验ReactiveUI(5.5.1)，我已经创建了一个ViewModel (ReactiveObject的子类)，它作为自动完成用于位置搜索(改编自mikebluestein/ReactiveUIDemo on github)。每次查询文本更改时，将调用一个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，DoSearchAsync(string query, CancellationToken cancellationToken)是可取消的，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。在这个特定的用例中取消请求似乎有点过分，但是我想知道在这个reactiveUI/async-Task场景中如何启用取消。

代码:

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;
}

}

在reactiveuiviewmodel (ReactiveObject)中取消异步任务

X没有内置这个功能，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));

更新ReactiveUI 9。x:

定义属性
// using ReactiveUI.Fody
[Reactive]
public ReactiveCommand<TQuery, IEnumerable<TResult> SearchCommand { get; set; }
private CompositeDisposable Disposables { get; } = new CompositeDisposable();
构造函数中的

// hook up the command
var searchCommand = ReactiveCommand.CreateFromTask<TQuery, IEnumerable<TResult>>((query, ct) => DoSearchAsync(query, ct)));
SearchCommand = searchCommand;
// don't forget to subscribe and dispose
searchCommand
    .Subscribe(result => Result = result)
    .DisposeWith(Disposables);

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