标签：index convert ToList Items ICollection IEnumerable Cannot
Cannot convert from an IEnumerable<T> to an ICollection<T>
I have defined the following:
public ICollection<Item> Items { get; set; }When I run this code:
Items = _item.Get("001");I get the following message:
Error 3
Cannot implicitly convert type
'System.Collections.Generic.IEnumerable<Storage.Models.Item>' to
'System.Collections.Generic.ICollection<Storage.Models.Item>'.
An explicit conversion exists (are you missing a cast?)
Can someone explain what I am doing wrong. I am very confused about the difference between Enumerable, Collections and using the ToList()
Added information
Later in my code I have the following:
for (var index = 0; index < Items.Count(); index++) Would I be okay to define Items as an IEnumerable?
回答1
ICollection<T> inherits from IEnumerable<T> so to assign the result of
IEnumerable<T> Get(string pk)
to an ICollection<T> there are two ways.
// 1. You know that the referenced object implements `ICollection<T>`,
// so you can use a cast
ICollection<T> c = (ICollection<T>)Get("pk");
// 2. The returned object can be any `IEnumerable<T>`, so you need to
// enumerate it and put it into something implementing `ICollection<T>`.
// The easiest is to use `ToList()`:
ICollection<T> c = Get("pk").ToList();The second options is more flexible, but has a much larger performance impact. Another option is to store the result as an IEnumerable<T> unless you need the extra functionality added by the ICollection<T> interface.
Additional Performance Comment
The loop you have
for (var index = 0; index < Items.Count(); index++)works on an IEnumerable<T> but it is inefficient; each call to Count() requires a complete enumeration of all elements. Either use a collection and the Count property (without the parenthesis) or convert it into a foreach loop:
foreach(var item in Items)
评论
ICollection<T> can be manipulated (see the doc for details), while an IEnumerable<T> can only be enumerated.
– Anders Abel
Jan 1, 2012 at 11:09
You cannot convert directly from IEnumerable<T> to ICollection<T>. You can use ToList method of IEnumerable<T> to convert it to ICollection<T>
someICollection = SomeIEnumerable.ToList();
标签：index,convert,ToList,Items,ICollection,IEnumerable,Cannot 来源： https://www.cnblogs.com/chucklu/p/16669578.html
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