How do you concatenate Lists in C#?

If I have:

List<string> myList1;
List<string> myList2;

myList1 = getMeAList();
// Checked myList1, it contains 4 strings

myList2 = getMeAnotherList();
// Checked myList2, it contains 6 strings

myList1.Concat(myList2);
// Checked mylist1, it contains 4 strings... why?

I ran code similar to this in Visual Studio 2008 and set break points after each execution. After myList1 = getMeAList();, myList1 contains four strings, and I pressed the plus button to make sure they weren't all nulls.

After myList2 = getMeAnotherList();, myList2 contains six strings, and I checked to make sure they weren't null... After myList1.Concat(myList2); myList1 contained only four strings. Why is that?

Solution 1:

Concat returns a new sequence without modifying the original list. Try myList1.AddRange(myList2).

Solution 2:

Try this:

myList1 = myList1.Concat(myList2).ToList();

Concat returns an IEnumerable<T> that is the two lists put together, it doesn't modify either existing list. Also, since it returns an IEnumerable, if you want to assign it to a variable that is List<T>, you'll have to call ToList() on the IEnumerable<T> that is returned.

Solution 3:

targetList = list1.Concat(list2).ToList();

It's working fine I think so. As previously said, Concat returns a new sequence and while converting the result to List, it does the job perfectly.