CODEWITHSUNDEEP
c#reflection
Phil Peace
Phil Peace

Reputation: 753

Adding an item to a generic List<T> with Reflection

Edit: Move along please, nothing to see here.

The solution to this question had nothing to do with Reflection and everything to do with me not paying attention to the implementation of the collection property in a base class.

I'm trying to add an item to a collection using Reflection using the following method:

public void AddReferenceToCollection(object targetResource, string propertyName, object resourceToBeAdded)
{
    Type targetResourceType = targetResource.GetType();
    PropertyInfo collectionPropertyInfo = targetResourceType.GetProperty(propertyName);

    // This seems to get a copy of the collection property and not a reference to the actual property
    object collectionPropertyObject = collectionPropertyInfo.GetValue(targetResource, null);
    Type collectionPropertyType = collectionPropertyObject.GetType();
    MethodInfo addMethod = collectionPropertyType.GetMethod("Add");

    if (addMethod != null)
    {
        // The following works correctly (there is now one more item in the collection), but collectionPropertyObject.Count != targetResource.propertyName.Count
        collectionPropertyType.InvokeMember("Add", System.Reflection.BindingFlags.InvokeMethod, null, collectionPropertyObject, new[] { resourceToBeAdded });
    }
    else
    {
        throw new NotImplementedException(propertyName + " has no 'Add' method");
    }
}

However, it appears that the call to targetResource.GetType().GetProperty(propertyName).GetValue(targetResource, null) returns a copy of targetResource.propertyName and not a reference to it and so the subsequent call to collectionPropertyType.InvokeMember affects the copy and not the reference.

How can I add the resourceToBeAdded object to the propertyName collection property of the targetResource object?

Upvotes: 1

Views: 2666

Answers (1)

Magnus
Magnus

Reputation: 46919

Try this:

public void AddReferenceToCollection(object targetResource, string propertyName, object resourceToBeAdded)
{
    var col = targetResource.GetType().GetProperty(propertyName).GetValue(targetResource, null) as IList;
    if(col != null)
        col.Add(resourceToBeAdded);
    else
        throw new InvalidOperationException("Not a list");
}

Edit: Test usage

void Main()
{

    var t = new Test();
    t.Items.Count.Dump(); //Gives 1
    AddReferenceToCollection(t, "Items", "testItem");
    t.Items.Count.Dump(); //Gives 2
}
public class Test
{
    public IList<string> Items { get; set; }

    public Test()
    {
        Items = new List<string>();
        Items.Add("ITem");
    }
}

Upvotes: 4

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