如何创建列表 <unknown type at compile time> 并通过System.Reflection.PropertyInfo复制项目

Question

I have come across something pretty complex. I would be obliged if anyone can help.

1) I have to create a List<> of unknown type at compile time. That I have already achieved.

 Type customList = typeof(List<>).MakeGenericType(tempType);
 object objectList = (List<object>)Activator.CreateInstance(customList);

"temptype" is the custom type thats been already fetched.

2) Now I have PropertyInfo object which is that list from which I have to copy all items to the the instance that I have just created "objectList"

3) Then I need to iterate and access the items of "objectList" as if it were a "System.Generic.List".

Cutting long story short, using reflection I need to extract a property that is a list and have it as an instance for further use. Your suggestions would be appreciated. Thanks in Advance.

Umair

Answer 1

Many of the .NET generic collection classes also implement their non-generic interfaces. I'd make use of these to write your code.

// Create a List<> of unknown type at compile time.
Type customList = typeof(List<>).MakeGenericType(tempType);
IList objectList = (IList)Activator.CreateInstance(customList);

// Copy items from a PropertyInfo list to the object just created
object o = objectThatContainsListToCopyFrom;
PropertyInfo p = o.GetType().GetProperty("PropertyName");
IEnumerable copyFrom = p.GetValue(o, null);
foreach(object item in copyFrom) objectList.Add(item); // Will throw exceptions if the types don't match.

// Iterate and access the items of "objectList"
// (objectList declared above as non-generic IEnumerable)
foreach(object item in objectList) { Debug.WriteLine(item.ToString()); }

Answer 2

I came up with something similar. I borrowed the SetProperties() method from NullSkull and wrote a simple method that calls the NullSkull SetProperties() :

    public static List<U> CopyList<T, U>(List<T> fromList, List<U> toList)
    {
        PropertyInfo[] fromFields = typeof(T).GetProperties();
        PropertyInfo[] toFields = typeof(U).GetProperties();
        fromList.ForEach(fromobj =>
        {
            var obj = Activator.CreateInstance(typeof(U));
            Util.SetProperties(fromFields, toFields, fromobj, obj);
            toList.Add((U)obj);
        });

        return toList;
    }

...so with one line of code I can retrieve a List<desired class> populated with matching values by name from List<source class> as follows:

List<desired class> des = CopyList(source_list, new List<desired class>());

As far as performance goes, I didn't test it, as my requirements call for small lists.

Answer 3

Do you think this would help you? Efficient way of updating a collection from another collection