T＆GT;不能从IEnumerable＆LT转换;到ICollection的＆LT; T＆GT; [英] Cannot convert from an IEnumerable<T> to an ICollection<T>

问题描述

我定义如下：

public ICollection<Item> Items { get; set; }

当我运行此code：

Items = _item.Get("001");

我得到以下信息：

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?)

有人能解释什么，我做错了。我很困惑的 间可枚举，集合和使用了ToList差（）

Can someone explain what I am doing wrong. I am very confused about the difference between Enumerable, Collections and using the ToList()

补充信息

后来在我的code我有以下几点：

Later in my code I have the following:

for (var index = 0; index < Items.Count(); index++) 

我会好起来的定义项目作为一个IEnumerable

Would I be okay to define Items as an IEnumerable?

推荐答案

的ICollection＆LT; T＆GT; 从继承了IEnumerable＆LT; T＆GT; 这样的结果分配

IEnumerable<T> Get(string pk)

到的ICollection＆LT; T＆GT; 有两种方法

// 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();

第二选项是更灵活，但具有大得多的性能影响。另一种选择是存储结果为的IEnumerable＆LT; T＆GT; 除非你需要用的ICollection＆LT添加了额外的功能; T＆GT; 接口。

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.

您的循环

for (var index = 0; index < Items.Count(); index++)

适用于一个的IEnumerable＆LT; T＆GT; ，但效率不高;每次调用计数（）需要的完全的枚举的所有元素。无论是使用集合和计数属性（不带括号），或者将其转换成一个foreach循环：

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)

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