如何在vb.net中使用DispatcherOperationCallback

Question

我在使用 DispatcherOperationCallback 将 c# 转换为 vb.net 时遇到问题。

我尝试根据 将 c# 匿名转换为 vb 的帮助来转换它。 net

我正在使用 VS2010。

我有这样的 c# 代码：

    public void Callback(Contract contract)
    {
        Dispatcher.BeginInvoke(DispatcherPriority.Normal,
              (DispatcherOperationCallback)delegate(object arg)
              {
                  Contract obj = (Contract)arg;
                  txtRequest.Text = HandleArgument(obj);                      
                  return null;
              }, contract);
    }

在我尝试像这样更改为 vb.net 之后，

Public Sub Callback(ByVal contract As Contract) Implements IServiceCallback.Callback

    Dispatcher.BeginInvoke(New DispatcherOperationCallback(Sub(arg As Object)
                                                           txtRequest.Text = HandleArgument(DirectCast(arg, Contract))
                                                           End Sub), DispatcherPriority.Normal, contract)

End Sub

但它不起作用。 vs2010显示“嵌套子没有与委托兼容的签名“委托函数DispatcherOperationCallback(arg As Object) As Object”

谢谢您的帮助。

Answer 1

只需阅读错误消息：

nested sub does not have a signature that is compatible with delegate 
  "Delegate Function DispatcherOperationCallback(arg As Object) As Object

因此，您应该相应地更改代码。

Public Sub Callback(ByVal contract As Contract) Implements IServiceCallback.Callback
    Dispatcher.BeginInvoke(
      New DispatcherOperationCallback(
          Function(arg As Object)
              txtRequest.Text = HandleArgument(DirectCast(arg, Contract))
              Return Nothing ' // you need to check what should be returned here '
          End Function), 
         DispatcherPriority.Normal, 
         contract)
End Sub