C#泛型列表<T>如何获取T的类型？

C# generic list <T> how to get the type of T?

提问by

I'm working on a reflection project, and now I'm stuck.

我正在做一个反射项目，现在我被卡住了。

If I have an object of myclassthat can hold a List<SomeClass>, does anyone know how to get the type as in the code below if the property myclass.SomListis empty?

如果我有一个myclass可以容纳 a的对象，List<SomeClass>如果属性myclass.SomList为空，有没有人知道如何获取下面代码中的类型？

List<myclass> myList = dataGenerator.getMyClasses();
lbxObjects.ItemsSource = myList; 
lbxObjects.SelectionChanged += lbxObjects_SelectionChanged;

private void lbxObjects_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    Reflect();
}

Private void Reflect()
{
    foreach (PropertyInfo pi in lbxObjects.SelectedItem.GetType().GetProperties())
    {
        switch (pi.PropertyType.Name.ToLower())
        {
            case "list`1":
            {           
                // This works if the List<T> contains one or more elements.
                Type tTemp = GetGenericType(pi.GetValue(lbxObjects.SelectedItem, null));

                // but how is it possible to get the Type if the value is null? 
                // I need to be able to create a new object of the type the generic list expect. 
                // Type type = pi.getType?? // how to get the Type of the class inside List<T>?
                break;
            }
        }
    }
}

private Type GetGenericType(object obj)
{
    if (obj != null)
    {
        Type t = obj.GetType();
        if (t.IsGenericType)
        {
            Type[] at = t.GetGenericArguments();
            t = at.First<Type>();
        } 
        return t;
    }
    else
    {
        return null;
    }
}

采纳答案by Marc Gravell

Type type = pi.PropertyType;
if(type.IsGenericType && type.GetGenericTypeDefinition()
        == typeof(List<>))
{
    Type itemType = type.GetGenericArguments()[0]; // use this...
}

---

---

More generally, to support any IList<T>, you need to check the interfaces:

更一般地，要支持 any IList<T>，您需要检查接口：

foreach (Type interfaceType in type.GetInterfaces())
{
    if (interfaceType.IsGenericType &&
        interfaceType.GetGenericTypeDefinition()
        == typeof(IList<>))
    {
        Type itemType = type.GetGenericArguments()[0];
        // do something...
        break;
    }
}

回答by GaryJL

Marc's answer is the approach I use for this, but for simplicity (and a friendlier API?) you can define a property in the collection base class if you have one such as:

Marc 的答案是我为此使用的方法，但为了简单起见（和更友好的 API？），如果您有以下属性，您可以在集合基类中定义一个属性：

public abstract class CollectionBase<T> : IList<T>
{
   ...

   public Type ElementType
   {
      get
      {
         return typeof(T);
      }
   }
}

I have found this approach useful, and is easy to understand for any newcomers to generics.

我发现这种方法很有用，并且对于泛型的任何新手来说都很容易理解。

回答by Colonel Panic

Given an object which I suspect to be some kind of IList<>, how can I determine of whatit's an IList<>?

给定一个对象，我怀疑是某种的IList<>，我怎么能确定的东西它是一个IList<>？

Here's a reliable solution. My apologies for length - C#'s introspection API makes this suprisingly difficult.

这是一个可靠的解决方案。我很抱歉，因为 C# 的内省 API 使这变得非常困难。

/// <summary>
/// Test if a type implements IList of T, and if so, determine T.
/// </summary>
public static bool TryListOfWhat(Type type, out Type innerType)
{
    Contract.Requires(type != null);

    var interfaceTest = new Func<Type, Type>(i => i.IsGenericType && i.GetGenericTypeDefinition() == typeof(IList<>) ? i.GetGenericArguments().Single() : null);

    innerType = interfaceTest(type);
    if (innerType != null)
    {
        return true;
    }

    foreach (var i in type.GetInterfaces())
    {
        innerType = interfaceTest(i);
        if (innerType != null)
        {
            return true;
        }
    }

    return false;
}

Example usage:

用法示例：

    object value = new ObservableCollection<int>();
Type innerType;
TryListOfWhat(value.GetType(), out innerType).Dump();
innerType.Dump();

Returns

退货

True
typeof(Int32)

回答by Colonel Panic

Given an object which I suspect to be some kind of IList<>, how can I determine of whatit's an IList<>?

给定一个对象，我怀疑是某种的IList<>，我怎么能确定的东西它是一个IList<>？

Here's the gutsy solution. It assumes you have the actual object to test (rather than a Type).

这是勇敢的解决方案。它假设您有要测试的实际对象（而不是 a Type）。

public static Type ListOfWhat(Object list)
{
    return ListOfWhat2((dynamic)list);
}

private static Type ListOfWhat2<T>(IList<T> list)
{
    return typeof(T);
}

Example usage:

用法示例：

object value = new ObservableCollection<DateTime>();
ListOfWhat(value).Dump();

Prints

印刷

typeof(DateTime)