英文:
Unable to cast to object
问题
我有一个代码：
var result = BOBase.Search(Mapper.SourceBrowserType, searchCriteria);
var list = new List<IBO>(result.OfType<IBO>());
但我需要能够向列表中添加许多元素。我尝试过：
var list = new List<IBO>();
var result = BOBase.Search(Mapper.SourceBrowserType, searchCriteria);
list.Add((IBO)result.OfType<IBO>());
这导致错误：
无法将类型为 ''<OfTypeIterator>d__95`1[BO.IBO]'' 的对象转换为类型 ''BO.IBO''。
如何解决这个问题？
英文:
I had a code:
var result = BOBase.Search(Mapper.SourceBrowserType, searchCriteria);
var list = new List<IBO>(result.OfType<IBO>());
But I need to be able to add many elements in a list. I tried:
var list = new List<IBO>();
var result = BOBase.Search(Mapper.SourceBrowserType, searchCriteria);
list.Add((IBO)result.OfType<IBO>());
Which results in an error:
Unable to cast object of type '<OfTypeIterator>d__95`1[BO.IBO]' to type 'BO.IBO'.
How to resolve this?
答案1
得分: 3
"OfType"将返回一个集合：IEnumerable<TResult>。问题在于，您试图将整个集合转换为单个元素。因此出现错误消息。
转换已经由"OfType"调用执行。您需要使用不同的添加方法。它被称为AddRange。
> 将指定集合的元素添加到List<T>的末尾。
list.AddRange(result.OfType<IBO>());
英文:
OfType will return a collection: IEnumerable<TResult>. The problem is that you try to cast this entire collection to a single element. Hence the error message.
The cast is already performed by the OfType call. You would need a different adding method. It is called AddRange.
> Adds the elements of the specified collection to the end of the List<T>.
list.AddRange(result.OfType<IBO>());
答案2
得分: 1
第二个代码片段应使用 AddRange，无需额外转换为 IBO：
> 将指定集合的元素添加到 List<T> 的末尾。
var list = new List<IBO>();
var result = BOBase.Search(Mapper.SourceBrowserType, searchCriteria);
list.AddRange(result.OfType<IBO>());
请注意，这两个代码片段将执行相同的操作。如果只有一个源集合，只需使用第一个。
英文:
The second snippet should use AddRange without extra casting to IBO:
> Adds the elements of the specified collection to the end of the List<T>.
var list = new List<IBO>();
var result = BOBase.Search(Mapper.SourceBrowserType, searchCriteria);
list.AddRange(result.OfType<IBO>());
Note that both snippets will doe the same. If you have only one source collection then just use the first one.
答案3
得分: 0
只需使用期望一个 IEnumerable<IBO> 参数的构造函数，无需额外的 Add*** 调用：
var list = new List<IBO>(result.OfType<IBO>());
但我需要能够在列表中添加许多元素。
实际上，上述代码正是如此：它将指定类型的所有元素添加到您新创建的列表中。
或者可以使用以下方式：
var list = result.OfType<IBO>().ToList();
英文:
You don't need an extra Add***-call, just use the constructor that expects an IEnumerable<IBO>:
var list = new List<IBO>(result.OfType<IBO>());
> But I need to be able to add many elements in a list.
In fact the above does exactly that: it adds all the elements of the specified type into your newly created list.
Alternativly use this:
var list = result.OfType<IBO>().ToList();
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