How Can I Determine the Type `T` of an Empty Generic List in C#?

C# generic listList<T>: Determine the type of T

In C#, a generic list allows you to store elements of a specific type. But what if you need to determine the T type of an empty generic list?

Consider the following scenario:

<code class="language-csharp">List<myclass> myList = dataGenerator.getMyClasses();
lbxObjects.ItemsSource = myList;
lbxObjects.SelectionChanged += lbxObjects_SelectionChanged;</code>

In the lbxObjects_SelectionChanged event, you are using reflection to retrieve information about the properties of the selected object. For a generic list (List<T>), you want to get the type of the elements it holds.

For this you can use the GetGenericType method, this method works if the list contains elements. However, this method fails when the list is empty. To overcome this problem, you need to access the type information whether any elements are present or not.

The solution lies in checking the attribute type stored in pi.PropertyType. The following is the modified code:

<code class="language-csharp">// 如果List<T>包含一个或多个元素，则此方法有效。
Type tTemp = GetGenericType(pi.GetValue(lbxObjects.SelectedItem, null));

// 如果列表为空，使用以下方法获取T的类型
Type type = pi.PropertyType;
if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(List<>))
{
    Type itemType = type.GetGenericArguments()[0];
    // 在此处使用itemType...
}</code>

Alternatively, for more comprehensive support, you can check the interfaces implemented by this type:

<code class="language-csharp">foreach (Type interfaceType in type.GetInterfaces())
{
    if (interfaceType.IsGenericType && interfaceType.GetGenericTypeDefinition() == typeof(IList<>))
    {
        Type itemType = interfaceType.GetGenericArguments()[0];
        // 对itemType执行某些操作...
        break;
    }
}</code>

With these methods, you can effectively determine the Ttype of generic lists, regardless of whether they contain any elements.

This revised output maintains the original image and improves the code formatting for better readability. The key changes are using List<> instead of List in the typeof check for better type matching and improving the overall flow and clarity of the explanation.

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