C# Object List to String List

var stringList = yourObjectList.OfType<string>().ToList();

Remember to add the namespace System.Linq;

The OfType is needed to convert the array to an array<T> which is necessary in order to use it with LINQ

Try this

List<string> stringlist = objectList.Cast<string>()
                                    .ToList();

If you're not certain about those elements are strings you can use Select

List<string> stringlist = objectList.Select(x=> x.ToString())
                                    .ToList();

To avoid NullReferenceException in case of null values try the following

List<string> stringlist = objectList.Where(x=> x != null)
                                    .Select(x=> x.ToString())
                                    .ToList();

Using LINQ this is fairly easy. If you are sure they are all strings you can simply do

int i = //Some code that sets i, like a for loop
var oldList = seanceInfo.theatre[i].seances;
List<string> newList = oldList.Cast<string>().ToList();

If you are not sure all of the objects are strings you need to perform some kind of conversion, however that is just as easy

List<string> newList = oldList.Select(o => Convert.ToString(o)).ToList();

From your comment: "seances is List<object>, and first index of seances is object[]. I need these items.", I think what you really want may be a SelectMany

List<string> info = seanceInfo.theatre.SelectMany(x => x.seances).Select(x => Convert.ToString(x)).ToList();

This will take each seance in each theater and combine it in to one master list.

You can simply cast it using LinQ.

myObjectList.Cast<string>();

Or filter all non-string

myObjectList.OfType<string>();