在 VB.NET 中转换为 List(Of T)
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Casting to List(Of T) in VB.NET
提问by CrispinH
In C# it's possible to cast to List<T>- so if you have:
在 C# 中，可以强制转换为List<T>- 所以如果你有：
List<Activity> _Activities;
List<T> _list;
The following will work:
以下将起作用：
_list = _Activities as List<T>;
but the translated line with VB.NET which is:
但是 VB.NET 的翻译行是：
_list = TryCast(_Activities, List(Of T))
throws a compilation error. So I've had a good hunt around and experimented with LINQ to find a way round this to no avail. Any ideas anyone?
引发编译错误。因此，我四处寻找并尝试了 LINQ 以找到解决此问题的方法，但无济于事。任何人的想法？
Thanks
谢谢
Crispin
克里斯平
回答by Hans Passant
I repro, this should technically be possible. Clearly the compiler doesn't agree. The workaround is simple though:
我重复，这在技术上应该是可能的。显然编译器不同意。不过解决方法很简单：
Dim _Activities As New List(Of Activity)
Dim o As Object = _Activities
Dim tlist = TryCast(o, List(Of T))
Or as a one-liner:
或者作为单线：
Dim tlist = TryCast(CObj(_Activities), List(Of T))
The JIT compiler should optimize the temporary away so it doesn't cost anything.
JIT 编译器应该优化临时的，这样它就不会花费任何费用。
回答by Jay Riggs
You can use the generic List.ConvertAllmethod.
您可以使用通用List.ConvertAll方法。
Given a List the method will return a List of a different type using a converter function you supply.
给定一个 List，该方法将使用您提供的转换器函数返回一个不同类型的 List。
The MSDN article I linked has an excellent example.
我链接的 MSDN 文章有一个很好的例子。
回答by Nate
I always use DirectCast(object, type)
我总是用 DirectCast(object, type)
