Question

我有这样的方法

public void LoadProgrammeListFromChannel(TVDailyScheduleParam scheduleParam, Action callback)
        {
            string url = Helper.GetProgrammeUrl(scheduleParam.Day, scheduleParam.Channel.Id); //1//
            WebClient client = new WebClient(); //2//

            client.OpenReadCompleted += new OpenReadCompletedEventHandler((sender, e) => //3//
            {//5//
                if (e.Error != null)
                    return;

                try
                {
                    _programmeList.Clear();
                    _programmeList = DataService.GetProgrammeList(e.Result);
                    // call method in MainVM to update View
                    callback();
                }
                finally
                {
                    // close file stream
                    e.Result.Close();
                }
            });

            client.OpenReadAsync(new Uri(url, UriKind.Absolute)); //4//
        }

我有这样的照片

LoadWhatsonProgrammeCommand = new RelayCommand(()=>
            {
                foreach (TVDailyScheduleParam param in _tvDailyScheduleVM.ChannelList.Select(c => new TVDailyScheduleParam(DateTime.Today, c, false)))
                {
                    TVDailyScheduleParam param2 = param;

                    _tvDailyScheduleVM.LoadProgrammeListFromChannel(param2, ()=>
                    {
                        RaisePropertyChanged(TV_DAILY_SCHEDULE_VM);
                    });

                    _tvDailyScheduleVM.GetWhatsonProgramme(param2, ()=>
                    {
                        RaisePropertyChanged(TV_DAILY_SCHEDULE_VM);
                    });
                }
            });

现在我调用命令时。首先，它运行_tvDailyScheduleVM.LoadProgrammeListFromChannel并调用LoadProgrammeListFromChannel方法。

在LoadProgrammeListFromChannel方法中，它从1开始运行 - > 2 - ＆gt; 3.在3，它没有完成，它运行到4然后回到命令并继续运行_tvDailyScheduleVM.GetWhatsonProgramme。

但_programmeList in LoadProgrammeListFromChannel未更新，因此GetWhatsonProgramme无法准确运行。

如何在运行LoadProgrammeListFromChannel之前返回_programmeList以运行3更新_tvDailyScheduleVM.GetWhatsonProgramme？

Answer 1

您描述的行为是“按设计”。您的方法LoadProgrammeListFromChannel进行异步调用。这意味着在您的方法中，序列是1 - > 2 - ＆gt; 3 - ＆gt; 4 - ＆gt;返回 - ＆gt;在调用函数中执行代码 - ＆gt;那么晚些时候5然后回调。

结果LoadProgrammeListFromChannel和GetWhatsonProgramme并行执行。因此，如果GetWhatsonProgramme需要始终才能在LoadProgrammeListFromChannel之后运行，您将有权将GetWhatsonProgramme移至您的回调方法中，即

LoadWhatsonProgrammeCommand = new RelayCommand(()=> {
    var channelList = _tvDailyScheduleVM
                          .ChannelList
                          .Select(c => new TVDailyScheduleParam(
                              DateTime.Today, 
                              c, 
                              false
                          ));

    foreach (TVDailyScheduleParam param in channelList) {
        TVDailyScheduleParam param2 = param;

        _tvDailyScheduleVM.LoadProgrammeListFromChannel(param2, ()=> {
            RaisePropertyChanged(TV_DAILY_SCHEDULE_VM);

            _tvDailyScheduleVM.GetWhatsonProgramme(param2, ()=> {
                RaisePropertyChanged(TV_DAILY_SCHEDULE_VM);
            });
        });
    }
});

或者，您可以订阅ViewModel的PropertyChangedEvent，如果TV_DAILY_SCHEDULE_VM属性已更改，请从那里调用GetWhatsonProgramme，尽管这可能不太合适。

在继续在同一命令中运行第二个方法之前，在第一个方法中更新实例

1 个答案: