How to Determine the Generic Type Parameter of an Empty List in C#?

How to determine the generic type parameter of an empty list in C#?

In C#, using a generic list (List<t></t>) usually requires obtaining information about the type of the list elements. However, if the generic list is empty, getting this type becomes challenging.

A common approach is to use reflection to check the properties of an myclass object holding an empty list. However, using the property values ​​directly (as shown in the original code) will fail because the properties of an empty list are initialized to null.

To overcome this situation, a different approach is required:

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

This code first gets the PropertyType of the checked attribute. It then checks whether this type is a generic type and whether its generic type definition is typeof(List). If these conditions are met, the code will use the GetGenericArguments() method to extract the type of the list element.

Typically, in order to support any IList<t></t>, additional checks can be performed:

foreach (Type interfaceType in type.GetInterfaces())
{
    if (interfaceType.IsGenericType && interfaceType.GetGenericTypeDefinition() == typeof(IList<>))
    {
        Type itemType = interfaceType.GetGenericArguments()[0]; // 注意这里使用interfaceType
        // 执行某些操作...
        break;
    }
}

This code checks all interfaces that the type implements, identifying any generic interface that has a IList<t></t>generic type definition. It then extracts the element type in a similar way as before. Note that here we get the generic parameters from interfaceType, not type.

This revised explanation clarifies the process and corrects a minor error in the second code snippet. It also uses more descriptive headings and sentence structures.

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