How do I check if a given value is a generic list?

小开

Probably the best way would be to do something like this:

IList list = value as IList;


if (list != null)
{
// use list in here
}

This will give you maximum flexibility and also allow you to work with many different types that implement the IList interface.

小开

if(value is IList && value.GetType().GetGenericArguments().Length > 0)
{


}

小开

最佳答案

using System.Collections;


if(value is IList && value.GetType().IsGenericType) {


}

小开

 bool isList = o.GetType().IsGenericType
&& o.GetType().GetGenericTypeDefinition() == typeof(IList<>));

小开

public bool IsList(object value) {
return value is IList
|| IsGenericList(value);
}


public bool IsGenericList(object value) {
var type = value.GetType();
return type.IsGenericType
&& typeof(List<>) == type.GetGenericTypeDefinition();
}

小开

For you guys that enjoy the use of extension methods:

public static bool IsGenericList(this object o)
{
var oType = o.GetType();
return (oType.IsGenericType && (oType.GetGenericTypeDefinition() == typeof(List<>)));
}

So, we could do:

if(o.IsGenericList())
{
//...
}

小开

Based on Victor Rodrigues' answer, we can devise another method for generics. In fact, the original solution can be reduced to only two lines:

public static bool IsGenericList(this object Value)
{
var t = Value.GetType();
return t.IsGenericType && t.GetGenericTypeDefinition() == typeof(List<>);
}


public static bool IsGenericList<T>(this object Value)
{
var t = Value.GetType();
return t.IsGenericType && t.GetGenericTypeDefinition() == typeof(List<T>);
}

小开

Here's an implementation that works in .NET Standard, and works against interfaces:

    public static bool ImplementsGenericInterface(this Type type, Type interfaceType)
{
return type
.GetTypeInfo()
.ImplementedInterfaces
.Any(x => x.GetTypeInfo().IsGenericType && x.GetGenericTypeDefinition() == interfaceType);
}

And here are the tests (xunit):

    [Fact]
public void ImplementsGenericInterface_List_IsValidInterfaceTypes()
{
var list = new List<string>();
Assert.True(list.GetType().ImplementsGenericInterface(typeof(IList<>)));
Assert.True(list.GetType().ImplementsGenericInterface(typeof(IEnumerable<>)));
Assert.True(list.GetType().ImplementsGenericInterface(typeof(IReadOnlyList<>)));
}


[Fact]
public void ImplementsGenericInterface_List_IsNotInvalidInterfaceTypes()
{
var list = new List<string>();
Assert.False(list.GetType().ImplementsGenericInterface(typeof(string)));
Assert.False(list.GetType().ImplementsGenericInterface(typeof(IDictionary<,>)));
Assert.False(list.GetType().ImplementsGenericInterface(typeof(IComparable<>)));
Assert.False(list.GetType().ImplementsGenericInterface(typeof(DateTime)));
}

小开

I'm using the following code:

public bool IsList(Type type) => type.IsGenericType && (
(type.GetGenericTypeDefinition() == typeof(List<>))
|| (type.GetGenericTypeDefinition() == typeof(IList<>))
);