DispatcherTimer WPF 异步

Question

每次定时器调用时 UpdateDocumentsListFromServer UI 冻结 3 秒。如何在 .net 3.5 下以异步方式更新列表？

视图模型：

public class ShippingDocumentsRegisterViewModel : ViewModelBase
    {
        ShippingDocumentsModel model = new ShippingDocumentsModel();

        DispatcherTimer timer = new DispatcherTimer();

        BackgroundWorker BW = new BackgroundWorker();

        public ShippingDocumentsRegisterViewModel()
        {
            timer = new DispatcherTimer();
            timer.Tick += new EventHandler(UpdateDocumentsListFromServer);
            timer.Interval = new TimeSpan(0, 0, 10);
            timer.Start();

            this.Columns = model.InitializeColumns();
            BW.DoWork += UpdateDocumentsList;
            BW.RunWorkerAsync();
        }

        public void UpdateDocumentsList(object o, EventArgs args)
        {
            this.ShippingDocuments = model.GetDocuments();
        }

        public void UpdateDocumentsListFromServer(object o, EventArgs args)
        {
            // Taking a lot of time. How to do it async?
            var tempDocuments = model.GetDocumentsFromServer();
            foreach (var item in tempDocuments)
            {
                this.shippingDocuments.Add(item);
            }
            //
        }

        private ObservableCollection<ShippingDocument> shippingDocuments;

        public ObservableCollection<ShippingDocument> ShippingDocuments
        {
            get
            {
                return shippingDocuments;
            }

            private set
            {
                shippingDocuments = value;
                RaisePropertyChanged("ShippingDocuments");
            }
        }

        public ObservableCollection<ShippingDocumentColumDescriptor> Columns { get; private set; }

    }

GetDocumentsFromServer 看起来像

    public ObservableCollection<ShippingDocument> GetDocumentsFromServer()
    {
        System.Threading.Thread.Sleep(3000);
        return new ObservableCollection<ShippingDocument> { new ShippingDocument { Name = "Test" } };
    }

Answer 1

使用常规 Timer 并且只分配对 shippingDocuments 的访问。

Answer 2

如评论中所述，您可以使用 Timers 而不是 DispatcherTimer。 DispactherTimer 将访问 UIThread，其中 Timer 使用与线程池不同的线程。

此外，您可以从不同的线程向 UIThread 分派一个动作

Application.Current.Dispatcher.BeginInvoke(new Action(() =>
           {
               //Do some UI stuffs                   
           }));

希望对您有所帮助。

Answer 3

您还可以使用向 UI

报告进度的后台工作者

public ShippingDocumentsRegisterViewModel()
{

    BW.DoWork += UpdateDocumentsListFromServer;
    BW.RunWorkerCompleted += BW_RunWorkerCompleted;

    BW.WorkerReportsProgress = true;
    BW.ProgressChanged += UpdateGui;
    BW.RunWorkerAsync();
}
public void UpdateGui(object o, EventArgs args)
{
    foreach (var item in tempDocuments)
    {
        this.shippingDocuments.Add(item);
    }
}
public void UpdateDocumentsListFromServer(object o, EventArgs args)
{

    while (true) {
        System.Threading.Thread.Sleep(3000);

        tempDocuments = GetDocumentsFromServer();
        BW.ReportProgress(0);

    }
}

int num = 0;
public ShippingDocument[] GetDocumentsFromServer()
    {
        System.Threading.Thread.Sleep(3000);
        return new ShippingDocument[1] { new ShippingDocument { Name = "Test" + num++} };
    }

private ShippingDocument[] tempDocuments = new ShippingDocument[0];

Answer 4

只需使用 Task 和 Async/Await 将其卸载到新线程，如下所示：

public async void UpdateDocumentsListFromServer(object o, EventArgs args)
        {
            // This will execute async and return when complete
            await Task.Run(()=>{
              var tempDocuments = model.GetDocumentsFromServer();
              foreach (var item in tempDocuments)
              {
                  this.shippingDocuments.Add(item);
              }
            });
            //
        }

请记住，此更新是在与 UI 不同的线程上进行的。所以不允许触及 UI 线程上的任何东西，否则你会遇到线程问题。因此，如果 shippingDocuments 是在 UI 线程上创建的并且不是线程安全的，您可以改为 return 一个项目集合，然后添加它们：

public async void UpdateDocumentsListFromServer(object o, EventArgs args)
        {
            // Execute on background thread and put results into items
            var items = await Task.Run(()=>{
              var tempDocuments = model.GetDocumentsFromServer();                  
              return tempDocuments;
            });
            //add occurs on UI thread.
            this.shippingDocuments.AddRange(tempDocuments);
        }

DispatcherTimer WPF 异步

DispatcherTimer WPF async

c#

wpf

asynchronous

.net-3.5