我正在尝试调用 Web 服务并让我的代码等待该服务返回结果（或超时）。我的项目是 Silverlight 5，带有使用 .NET 4.0 的 Web 服务，我在 VS 2012 下使用 Microsoft.Bcl.Async.1.0.16\lib\sl4\Microsoft.Threading.Tasks.dll ... 任务运行这个项目。 Extensions.dll ... 和 Extensions.Silverlight.dll。
这就是我一直在做的事情并且它正在工作，但我正在尝试弄清楚如何更改我的代码，以便我可以使用 Async/Await 进程。Web 服务引用配置为在所有引用的程序集中返回 ObservableCollection 和 Generic.Dictionary 以及 Reuse 类型。
我需要转换为 Async/Await 的一些代码：
Private _Units As Collections.ObjectModel.ObservableCollection(Of DC.SL.Services.WebServiceUnit.Units)
Public Property Units() As Collections.ObjectModel.ObservableCollection(Of DC.SL.Services.WebServiceUnit.Units)
Get
Return _Units
End Get
Set(ByVal value As Collections.ObjectModel.ObservableCollection(Of DC.SL.Services.WebServiceUnit.Units))
_Units = value
OnPropertyChanged(New PropertyChangedEventArgs("Units"))
End Set
End Property
Public Sub ReadUnits()
Try
' Client is required
If Not Me.Client Is Nothing Then
' User is required
If Not Me.User Is Nothing Then
' Must be a real Client
If Me.Client.ClientID > 0 Then
' My have a sites
If Not Me.Site Is Nothing Then
' Call the web service relative to where this application is running
Dim webServiceURI As New Uri("../WebServices/Unit.svc", UriKind.RelativeOrAbsolute)
Dim webServiceAddress As New EndpointAddress(webServiceURI)
' Setup web Service proxy
Dim wsUnits As New DC.SL.Services.WebServiceUnit.UnitClient
wsUnits.Endpoint.Address = webServiceAddress
' Add event handler so we can trap for web service completion
AddHandler wsUnits.LoadsCompleted, AddressOf LoadUnitsCompleted
' Call web service to get Sites the user has access to
wsUnits.LoadsAsync(Me.Client, Me.Site.SiteID, Me.Size.SizeID, Me.RentalType.RentalTypeID, Me.UnitState)
End If
End If
End If
End If
Catch ex As Exception
Dim Problem As New DC.SL.Tools.Errors(ex)
End Try
End Sub
Private Sub LoadUnitsCompleted(ByVal sender As Object, ByVal e As DC.SL.Services.WebServiceUnit.LoadsCompletedEventArgs)
Try
If Not IsNothing(e.Result) Then
Me.Units = e.Result
If Me.Units.Count > 0 Then
Me.Unit = Me.Units.Item(0)
End If
End If
Catch ex As Exception
Dim Problem As New DC.SL.Tools.Errors(ex)
End Try
End Sub
仍然没有让这个工作......这是我现在所拥有的，但问题仍然存在...... UI线程执行继续并且不等待Web服务调用完成。
调用代码：
ReadUnitsAsync().Wait(3000)
这是更新的代码：
Public Async Function ReadUnitsAsync() As Task(Of Boolean)
Dim Results As Object = Await LoadReadUnitsAsync()
Return True
End Function
Public Function LoadReadUnitsAsync() As Task(Of System.Collections.ObjectModel.ObservableCollection(Of DC.SL.Services.WebServiceUnit.Units))
LoadReadUnitsAsync = Nothing
Dim tcs = New TaskCompletionSource(Of System.Collections.ObjectModel.ObservableCollection(Of DC.SL.Services.WebServiceUnit.Units))
' Client is required
If Not Me.Client Is Nothing Then
' User is required
If Not Me.User Is Nothing Then
' Must be a real Client associated
If Me.Client.ClientID > 0 Then
' Only get associated sites IF we don't have any defined
If Not Me.Site Is Nothing Then
' Call the web service relative to where this application is running
Dim webServiceURI As New Uri("../WebServices/Unit.svc", UriKind.RelativeOrAbsolute)
Dim webServiceAddress As New EndpointAddress(webServiceURI)
' Setup Site web Service proxy
Dim wsUnits As New DC.SL.Services.WebServiceUnit.UnitClient
wsUnits.Endpoint.Address = webServiceAddress
' Add event handler so we can trap for web service completion
AddHandler wsUnits.LoadUnitsCompleted, Sub(s, e)
If e.Error IsNot Nothing Then
tcs.TrySetException(e.Error)
ElseIf e.Cancelled Then
tcs.TrySetCanceled()
Else
tcs.TrySetResult(e.Result)
End If
End Sub
'' Set Busy Status
'BusyStack.Manage(ProcessManager.StackAction.Add, "ReadUnits", Me.IsWorking, Me.IsWorkingMessage)
' Call web service to get Sites the user has access to
wsUnits.LoadUnitsAsync(Me.Client, Me.Site.SiteID, Me.Size.SizeID, Me.RentalType.RentalTypeID, Me.UnitState)
Return tcs.Task
End If
End If
End If
End If
End Function
所以这里是最终的代码（缩写），似乎可以达到我的目标（也就是在继续之前等待 Web 服务完成）。
Public Class UIUnits
Implements INotifyPropertyChanged, IDataErrorInfo
Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
Public Async Sub OnPropertyChanged(ByVal e As PropertyChangedEventArgs)
Dim propertyEventHandler As PropertyChangedEventHandler = PropertyChangedEvent
Try
If propertyEventHandler IsNot Nothing Then
RaiseEvent PropertyChanged(Me, e)
Select Case e.PropertyName
Case "Size"
Await ReadUnitsAsync()
DoSomethingElseAfterWebServiceCallCompletes()
Case Else
End Select
End If
Catch ex As Exception
Dim problem As New DC.SL.Tools.Errors(ex)
End Try
End Sub
...
Private _Units As Collections.ObjectModel.ObservableCollection(Of DC.SL.Services.WebServiceUnit.Units)
Public Property Units() As Collections.ObjectModel.ObservableCollection(Of DC.SL.Services.WebServiceUnit.Units)
Get
Return _Units
End Get
Set(ByVal value As Collections.ObjectModel.ObservableCollection(Of DC.SL.Services.WebServiceUnit.Units))
_Units = value
OnPropertyChanged(New PropertyChangedEventArgs("Units"))
End Set
End Property
...
Public Async Function ReadUnitsAsync() As Task(Of Boolean)
Me.Units = Await LoadReadUnitsAsync()
Return True
End Function
...
Public Function LoadReadUnitsAsync() As Task(Of System.Collections.ObjectModel.ObservableCollection(Of DC.SL.Services.WebServiceUnit.Units))
LoadReadUnitsAsync = Nothing
Dim tcs = New TaskCompletionSource(Of System.Collections.ObjectModel.ObservableCollection(Of DC.SL.Services.WebServiceUnit.Units))
' Client is required
If Not Me.Client Is Nothing Then
' User is required
If Not Me.User Is Nothing Then
' Must be a real Client associated
If Me.Client.ClientID > 0 Then
' Only get associated sites IF we don't have any defined
If Not Me.Site Is Nothing Then
' Call the web service relative to where this application is running
Dim webServiceURI As New Uri("../WebServices/Unit.svc", UriKind.RelativeOrAbsolute)
Dim webServiceAddress As New EndpointAddress(webServiceURI)
' Setup web Service proxy
Dim wsUnits As New DC.SL.Services.WebServiceUnit.UnitClient
wsUnits.Endpoint.Address = webServiceAddress
' Add event handler so we can trap for web service completion
AddHandler wsUnits.LoadUnitsCompleted, Sub(s, e)
If e.Error IsNot Nothing Then
tcs.TrySetException(e.Error)
ElseIf e.Cancelled Then
tcs.TrySetCanceled()
Else
tcs.TrySetResult(e.Result)
End If
End Sub
' Call web service
wsUnits.LoadUnitsAsync(Me.Client, Me.Site.SiteID, Me.Size.SizeID, Me.RentalType.RentalTypeID, Me.UnitState)
Return tcs.Task
End If
End If
End If
End If
End Function