c# - 从任务工厂调度的线程更新 WPF 中的 UI 的正确方法是什么？

Question

我正在尝试从通过 Task.Factory 调度的线程之一更新 UI .我很难正确更新我的 UI。

这是我观察到的行为:

Task.Factory.StartNew(() =>
    {
        // UI does get updated from here.
    }).ContinueWith(task =>
        {
            // UI does *not* get updated from here.
        });

在 Task Factory 调度的线程中更新 UI 的正确方法是什么？ ?

这是我的实际代码供您引用:

private string CurrentProcess
{
    set { _eventAggregator.GetEvent<CurrentProcessUpdatedEvent>().Publish(value); }
}

private double ProgressPercentage
{
    set
    {
        _eventAggregator.GetEvent<ProgressPercentageUpdatedEvent>()
                        .Publish(Utilities.GetProgressPercentage(value));
    }
}

TaskScheduler uiScheduler = TaskScheduler.FromCurrentSynchronizationContext();
var tasks = new List<Task<DataTable>>();

string siteCollectionUrl;
string connectionString;

try
{
    Dictionary<string, object> session = ApplicationContext.Current.Session;

    try
    {
        if ((double) session["ProgressPercentage"] > 0) return;
    }
    catch
    {
    }

    siteCollectionUrl = (string) session["SiteCollection"];
    connectionString = (string) session["Database"];
}
catch
{
    return;
}

_eventAggregator.GetEvent<IsProcessingChangedEvent>().Publish(true);
CurrentProcess = "Loading resources.";

Task<DataTable> spTask = Task<DataTable>.Factory.StartNew(() =>
    {
        using (ChannelFactory<ISharePointService> service = Utilities.GetSharePointService())
        {
            ISharePointService sharePointService = service.CreateChannel();
            DataTable spDatatable = sharePointService.GetResources(siteCollectionUrl);

            Task.Factory.StartNew(() => { ProgressPercentage = 10; }, CancellationToken.None, TaskCreationOptions.None, uiScheduler);

            return spDatatable;
        }
    });

tasks.Add(spTask);

Task<DataTable> buildTableTask = Task<DataTable>.Factory.ContinueWhenAll(tasks.ToArray(), t =>
    {
        DataTable spDatatable = t[0].Result;

        double percent = 10/spDatatable.Rows.Count;

        var columnMap = new Dictionary<string, string>
            {
                {"IsValid", null},
                {"Reason", null},
                {"SPID", "ID"},
                {"DBID", "EXTID"},
                {"Name", "Title"},
                {"Account", "SharePointAccount"},
                {"Email", "Email"},
                {"Generic", "Generic"},
                {"Department", "Department"},
                {"TempDept", "TempDept"},
                {"Role", "Role"},
                {"TempRole", "TempRole"},
                {"HolidaySchedule", "HolidaySchedule"},
                {"WorkHours", "WorkHours"}
            };

        DataTable spResources = BuildDataTable(columnMap);

        foreach (DataRow dataRow in spDatatable.Rows)
        {
            DataRow row = spResources.NewRow();

            foreach (var pair in columnMap)
            {
                try
                {
                    row[pair.Key] = dataRow[pair.Value];
                }
                catch
                {
                }
            }

            spResources.Rows.Add(row);

            Task.Factory.StartNew(() => { ProgressPercentage = percent; }, CancellationToken.None, TaskCreationOptions.None, uiScheduler);
        }

        return spResources;
    });

tasks.Add(buildTableTask);

Task<DataTable> dbTask = Task<DataTable>.Factory.StartNew(() =>
    {
        using (var sqlConnection = new SqlConnection(connectionString))
        {
            using (var sqlCommand = new SqlCommand(SQL, sqlConnection))
            {
                sqlConnection.Open();
                using (SqlDataReader sqlDataReader = sqlCommand.ExecuteReader())
                {
                    var dataTable = new DataTable();
                    dataTable.Load(sqlDataReader);

                    Task.Factory.StartNew(() => { ProgressPercentage = 10; }, CancellationToken.None, TaskCreationOptions.None, uiScheduler);

                    return dataTable;
                }
            }
        }
    });

tasks.Add(dbTask);

Task.Factory.ContinueWhenAll(tasks.ToArray(), t =>
    {
        DatabaseResources = t[2].Result;
        DataTable sharePointResources = t[1].Result;

        if (sharePointResources != null)
        {
            int resourceIndex = 1;
            int totalResources = sharePointResources.Rows.Count;
            double percentPoint = 70/totalResources;

            foreach (DataRow row in sharePointResources.Rows)
            {
                DataRow currentRow = row;

                Task.Factory.StartNew(() =>
                    {
                        CurrentProcess = string.Format("[{0}/{1}] Processing: {2}",
                                                        resourceIndex++, totalResources,
                                                        currentRow["Name"]);
                    }, CancellationToken.None, TaskCreationOptions.None, uiScheduler);

                bool isValid = true;
                var reasons = new List<string>();

                DataRow[] dataRows =
                    _databaseResources.Select(string.Format("ResourceID = {0}", row["DBID"]));
                if (dataRows.Any())
                {
                    DataRow dataRow = dataRows[0];

                    string tempDept = (row["TempDept"] ?? string.Empty).ToString();
                    string dept = (row["Department"] ?? string.Empty).ToString();

                    string tempRole = (row["TempRole"] ?? string.Empty).ToString();
                    string role = (row["Role"] ?? string.Empty).ToString();

                    string hs = (row["HolidaySchedule"] ?? string.Empty).ToString();
                    string dbhs = (dataRow["HolidaySchedule"] ?? string.Empty).ToString();

                    string wh = (row["WorkHours"] ?? string.Empty).ToString();
                    string dbwh = (dataRow["WorkHours"] ?? string.Empty).ToString();

                    if (string.IsNullOrEmpty(dept))
                    {
                        if (!dept.Equals(tempDept))
                        {
                            isValid = false;
                            reasons.Add("Department does not match Temp Dept");
                        }
                    }

                    if (string.IsNullOrEmpty(role))
                    {
                        if (!role.Equals(tempRole))
                        {
                            isValid = false;
                            reasons.Add("Role does not match Temp Role");
                        }
                    }

                    if (string.IsNullOrEmpty(hs))
                    {
                        if (!hs.Equals(dbhs))
                        {
                            isValid = false;
                            reasons.Add("Holiday Schedule does not match Holiday Schedule from database");
                        }
                    }

                    if (string.IsNullOrEmpty(wh))
                    {
                        if (!wh.Equals(dbwh))
                        {
                            isValid = false;
                            reasons.Add("Work Hours does not match Work Hours from database");
                        }
                    }
                }
                else
                {
                    isValid = false;
                    reasons.Add("Resource does not exist in database");
                }

                row["IsValid"] = isValid;
                row["Reason"] = string.Join("\n", reasons.ToArray());

                Task.Factory.StartNew(() => { ProgressPercentage = percentPoint; }, CancellationToken.None, TaskCreationOptions.None, uiScheduler);
            }

            SharePointResources = sharePointResources;
        }

        _eventAggregator.GetEvent<ProgressPercentageUpdatedEvent>()
                        .Publish(Utilities.ResetProgressPercentage());
        _eventAggregator.GetEvent<IsProcessingChangedEvent>().Publish(false);
    });

Answer 1

// UI does get updated from here

您应该启动 new Action(() =>通过 DispatcherObject在 WPF 中

Task.Factory.StartNew(() =>
    {
        // UI does get updated from here
        this.Dispatcher.BeginInvoke(new Action(() => 
        {

请搜索 Alexandra Rusina 的系列“.NET Framework 4 中的并行编程”的“ Part 1 - Getting Started”中的最后一行

我相信你会进一步享受这个引用的所有续集。

Part 2- Task Cancellation演示如何改用任务调度程序:

var ui = TaskScheduler.FromCurrentSynchronizationContext();
Task.Factory.ContinueWhenAll(tasks.ToArray(),
    result =>
    {
        var time = watch.ElapsedMilliseconds;
        label1.Content += time.ToString();
    }, CancellationToken.None, TaskContinuationOptions.None, ui);

代替:

Task.Factory.ContinueWhenAll(tasks.ToArray(),
      result =>
      {
          var time = watch.ElapsedMilliseconds;
          this.Dispatcher.BeginInvoke(new Action(() =>
              label1.Content += time.ToString()));
      });  

回应评论

"First of all, I am using PRISM. So, in my ViewModwl I have to use Dispatcher.Current.BeginInvoke --- I tried that. It did not help"

请查看 "Is WPF Dispatcher the solution of multi threading problems?" 的答案与在 Prism 中使用调度程序和访问 UI 相关:

// Not a UI component
public class MyDomainService : IMyDomainService
{
   private readonly IDispatcher _dispatcher;

   public MyDomainService(IDispatcher dispatcher) 
   {
      _dispatcher = dispatcher;
   }

   private void GotResultFromBackgroundThread()
   {
       _dispatcher.Dispatch(() => DoStuffOnForegroundThread());
   }
}

" You need to make sure you are invoking on the actual UI Dispatcher, not necessarily the Current "

您可以参与 the PRISM event aggregator确保您在 UI 线程或基本 Dispatcher.CheckAccess Method

如果你使用 TaskScheduler，那么你应该得到 TaskScheduler.FromCurrentSynchronizationContext在 UI 线程上(例如，在 Window.Loaded 事件处理程序中，您将双击您的表单)并传递/共享到/与任务。