1

注意：取决于这个问题

你好。我有一个像这样的视图模型：

public class ViewModel {
    private readonly IPersonService _personService;
    private readonly ObservableCollection<SearchPersonModel> _foundedList;
    private readonly DispatcherTimer _timer;
    private readonly Dispatcher _dispatcher;
    private CancellationTokenSource _tokenSource;

    public SearchPatientViewModel(IPersonService personService) {
        _personService = personService;
        _foundedList = new ObservableCollection<SearchPersonModel>();
        _dispatcher = (/*CurrentApplication*/).Dispatcher;
        _timer = new DispatcherTimer(
            TimeSpan.FromMilliseconds(1000),
            DispatcherPriority.Normal,
            TimerCallBack,
            _dispatcher);
        _tokenSource = new CancellationTokenSource();
    }

    public string Term {
        get { return _term; }
        set {
            // implementing INotifyPropertyChanged
            if(_term== value)
                return;
            _term= value;
            OnPropertyChanged(() => Term);
            tokenSource.Cancel(); // canceling prev search query
            _timer.Stop(); // stop the timer to reset it
            // start it again to do a search query if user change not the term for 1000ms
            _timer.Start(); 
        }
    }

    private void TimerCallBack(object sender, EventArgs e) {
        _timer.Stop();
        _tokenSource = new CancellationTokenSource();
        var task = Task<IEnumerable<SearchPersonModel>>.Factory
            .StartNew(Search, _tokenSource.Token);
        _dispatcher.BeginInvoke((Action)(() => {
            _foundedList.Clear();
            foreach(var item in task.Result)
                _foundedList.Add(item);
        }), DispatcherPriority.Background);
    }

    private IEnumerable<SearchPersonModel> Search() {
        return _personService.DoSearch(this.Term);
    }

}

在IPersonService实现中我这样做：

public class PersonService : IPersonService {
    public IEnumerable<SearchPersonModel> DoSearch(string term){
        System.Threading.Thread.Sleep(10000);
        return some-search-result;
    }
}

但是，我希望在执行搜索查询时，GUI 是免费的。但它冻住了！你知道我的错误在哪里吗？你能帮我吗？提前致谢！

4

1 回答 1

4

问题是评估task.Result将阻塞，直到查询完成。

最简单的选择可能是让Search方法在最后执行_dispatcher.BeginInvoke调用。

另一个选项 - 使用 C# 5 会变得更容易 - 将继续添加到任务中，以便在完成后您可以更新 UI。目前你会使用Task.ContinueWith; 对于 C# 5，您将使用asyncand await。

于 2012-05-10T12:50:06.647 回答