将不同类型的通用对象添加到通用列表中

本文介绍了将不同类型的通用对象添加到通用列表中的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

是否可以将不同类型的通用对象添加到列表中？如下。

Is it possible to add different type of generic objects to a list?. As below.

public class ValuePair<T> { public string Name { get; set;} public T Value { get; set; }

并说我拥有所有这些对象...

and let say I have all these objects...

ValuePair<string> data1 = new ValuePair<string>(); ValuePair<double> data2 = new ValuePair<double>(); ValuePair<int> data3 = new ValuePair<int>();

我想将这些对象保存在通用列表中，例如

I would like to hold these objects in a generic list.such as

List<ValuePair> list = new List<ValuePair>(); list.Add(data1); list.Add(data2); list.Add(data3);

有可能吗？

推荐答案

通常，您必须使用 List< object> 或创建非通用基类，例如

In general, you'd have to either use a List<object> or create a non-generic base class, e.g.

public abstract class ValuePair { public string Name { get; set;} public abstract object RawValue { get; } } public class ValuePair<T> : ValuePair { public T Value { get; set; } public object RawValue { get { return Value; } } }

然后，您可以拥有 List< ValuePair> ; 。

现在，有一个 例外：C＃4中的协变/反变量类型。例如，您可以编写：

Now, there is one exception to this: covariant/contravariant types in C# 4. For example, you can write:

var streamSequenceList = new List<IEnumerable<Stream>>(); IEnumerable<MemoryStream> memoryStreams = null; // For simplicity IEnumerable<NetworkStream> networkStreams = null; // For simplicity IEnumerable<Stream> streams = null; // For simplicity streamSequenceList.Add(memoryStreams); streamSequenceList.Add(networkStreams); streamSequenceList.Add(streams);

这不适用于您的情况，因为：

This isn't applicable in your case because:

• 您正在使用泛型类，而不是接口
• 您无法将其更改为泛型协变量接口，因为您有 T 进入了API的和出
• 您将值类型用作类型参数，而这些值类型不适用于泛型变量（因此 IEnumerable< int> 不是 IEnumerable< object> ）

• You're using a generic class, not an interface
• You couldn't change it into a generic covariant interface because you've got T going "in" and "out" of the API
• You're using value types as type arguments, and those don't work with generic variable (so an IEnumerable<int> isn't an IEnumerable<object>)