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c#reflectionlistgenerics
Jason
Jason

Reputation:

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

public bool IsList(object value)
    {
        Type type = value.GetType();
        // Check if type is a generic list of any type
    }

What's the best way to check if the given object is a list, or can be cast to a list?

Upvotes: 122

Views: 113683

Answers (9)

Yashar Aliabbasi
Yashar Aliabbasi

Reputation: 2719

I'm using the following code:

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

Upvotes: 6

James Couvares
James Couvares

Reputation: 1783

using System.Collections;

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

}

Upvotes: 122

Jeff Siemens
Jeff Siemens

Reputation: 81

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)));
    }

Upvotes: 8

Victor Rodrigues
Victor Rodrigues

Reputation: 11713

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())
{
 //...
}

Upvotes: 164

user1618054
user1618054

Reputation:

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>);
}

Upvotes: 6

Atif Aziz
Atif Aziz

Reputation: 36618

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();
}

Upvotes: 7

BFree
BFree

Reputation: 103742

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

}

Upvotes: 5

Eoin Campbell
Eoin Campbell

Reputation: 44268

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

Upvotes: 18

Andrew Hare
Andrew Hare

Reputation: 351456

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.

Upvotes: 1

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