带接口的字典声明错误 [英] Declaration Error of Dictionary with Interface

问题描述

我试图声明一个字典有一个字符串作为键，一个对象是一个值。我在接口的帮助下声明了它。这是我的代码

Hi,

I tried to declare a dictionary have a string as the key and an object a the value. I declared it with the help of the interfaces. This is my code

ICollection<KeyValuePair<string, ICollection<DemoProperty>>> Test = new Dictionary<string, List<DemoProperty>>();

它得到了转换错误。



但是当我声明如下时没有错误

Its getting the coversion Error.

But there is no Error when I declare as below

ICollection<KeyValuePair<string, ICollection<DemoProperty>>> Test = new List<KeyValuePair<string, ICollection<DemoProperty>>>();

我知道这可以声明如下

and I know this can declare as below also

Dictionary<string, ICollection<DemoProperty>> Test = new Dictionary<string, ICollection<DemoProperty>> 

第一个陈述的确切错误是什么，如何进行第一次陈述。希望大家都能理解我的问题。

What is the exact error on the first statement and how can I proceed with the first statatement. Hope you all understand my questions.

推荐答案

你不能在字典声明中重铸价值类型：

You cannot recast the value type at declaration of the dictionary:

ICollection<keyvaluepair><string,>>> Test = new Dictionary<string,>>();

Test.Add(new KeyValuePair<string,>>("a",new List<demoproperty>()));

</demoproperty></keyvaluepair>

如果可以，那么您将无法添加任何 ICollection ，只有列表< demoproperty> 这不是你的声明所说的





您可以将 ICollection< x> 实例化为词典< x> ，因为词典< tkey，tvalue> ;继承ICollection< tkey，tvalue>但是如果你改变泛型类型，那么它们将不匹配。

If you could then you would not be able to add any ICollection, only List<demoproperty> which is not what your declaration states


You can instantiate an ICollection<x> as a Dictionary<x> because Dictionary<tkey,tvalue>; inherits ICollection<tkey,tvalue> but if you change the generic types then they won't match.

在你的第一个声明中，你使用List而不是ICollection。这适用：

In your first declaration you use List instead of ICollection. This works:

ICollection<KeyValuePair<string, ICollection<DemoProperty>>> Test = new Dictionary<string, ICollection<DemoProperty>>();

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