请注意,我在此处了解其他yield in vb.net个问题。
我最近在玩Caliburn。那里有很多很棒的东西,包括co-routines实施。
我正在做的大部分工作都是基于C#的,但现在我也正在为基于Rob small MVVM framework的VB.NET商店创建一个架构指南。
除了使用VB的协同例程外,一切看起来都很顺利。由于使用了VB 10,我们可以尝试类似Bill McCarthy's suggestion:
的内容Public Function Lines(ByVal rdr as TextReader) As IEnumerable(Of String)
Return New GenericIterator(Of String)
(Function(ByRef nextItem As String) As Boolean
nextItem = rdr.ReadLine
Return nextItem IsNot Nothing
End Function)
End Function
我只是无法理解如何在VB中编写一个更复杂的协同常规方法(取自Rob的GameLibrary):
public IEnumerable<IResult> ExecuteSearch()
{
var search = new SearchGames
{
SearchText = SearchText
}.AsResult();
yield return Show.Busy();
yield return search;
var resultCount = search.Response.Count();
if (resultCount == 0)
SearchResults = _noResults.WithTitle(SearchText);
else if (resultCount == 1 && search.Response.First().Title == SearchText)
{
var getGame = new GetGame
{
Id = search.Response.First().Id
}.AsResult();
yield return getGame;
yield return Show.Screen<ExploreGameViewModel>()
.Configured(x => x.WithGame(getGame.Response));
}
else SearchResults = _results.With(search.Response);
yield return Show.NotBusy();
}
任何想法如何实现,或者在VB中使用Caliburn协同例程的任何想法?
修改
Marco向我指出了一个正确的方向。在查看Rob的GameLibrary的Reflector - Visual Basic代码后,我设法修改了Bill McCarthy的GenericIterator,成为一个穷人的状态机:
Private _state As Integer = -1
Public Function MoveNext() As Boolean Implements IEnumerator.MoveNext
_state += 1
Return _func(_Current, _state)
End Function
我们可以像这样使用它:
Public Function ExecuteSearch() As IEnumerable(Of String)
' If we need some variable shared across states, define it here
Dim someSharedStuff As String = String.Empty
' Notice the second lambda function parameter below - state
Return New GenericIterator(Of IResult)
(Function(ByRef nextItem As IResult, state As Integer) As Boolean
Select Case state
Case 0
someSharedStuff = "First state"
nextItem = Show.Busy
Return True
Case 1
nextItem = Show.SomeLoadingScreen
' Do some additional processing here...
Return True
Case 2
' Do something with someSharedStuff variable...
Console.WriteLine(someSharedStuff)
nextItem = PerforSomemWebServiceCall()
Return True
'...
Case 6
nextItem = Show.NotBusy
Return False
End Select
Return False
End Function)
End Function
它绝对不如C#版本那么优雅,但它看起来是可行的。我们将看看这是否有任何问题。如果有人有更好的想法,我会全力以赴。
答案 0 :(得分:3)
据我所知,VB的解决方法依赖于各个步骤的一致性;换句话说,它会重复相同的操作,直到满足退出条件。
相反,Caliburn协同程序在相反的情况下非常有用:与控制代码交错的非同构(和异步)步骤;但这基本上是一台状态机。实际上,Caliburn利用C#编译器获得免费且自动生成的状态机实现;因此,解决方案可能是构建一个简单的手工状态机,就像C#编译器构建的那样(参见http://blogs.msdn.com/wesdyer/archive/2007/03/23/all-about-iterators.aspx)。