检查List中是否存在不区分大小写的字符串

Question

I have an error with my List. Let me show you my idea: I have a loop, when finish loop 1, value will add to List, and it will continue when finish loop. Finally, i will a List that include all value in each loop.

Then, i want to check if value is exist in List. If exist, i will do something.

Example:

Loop 1: List: A

Loop 2: List: A,B

Loop 3: List: A,B,A

Because value A is Exist in List. Then, i will do some thing if A exist in List

List<string> list = new List<string>();
foreach (DataRow r in dt.Rows)
{
  string Url = r["Url"].ToString();
  list.Add(Url);
  if (list.Contains(Url, StringComparer.OrdinalIgnoreCase))
    {
      //dosomething
    }
}

But nothing happen. Wish you help me improve my code. Thanks !!!

Answer 1

Try like this

if(list.Where(o=> string.Equals(Url, o, StringComparison.OrdinalIgnoreCase)).Any())
{
   // Exists in the list
}

Or

if(list.FindIndex(o=> string.Equals(Url, o, StringComparison.OrdinalIgnoreCase))>-1){

  // Exists in the list
}

Answer 2

Better approach would be using the List methods Exists or Contains , checkout the following program:

List<string> l = new List<string>();
l.Add("Madrid");
l.Add("Barcelona");
l.Add("NewYork");
l.Add("Chicago");  
if(l.Exists(x=>string.Equals(x,"Chicago",StringComparison.OrdinalIgnoreCase))){
    Console.WriteLine("Done !!");
}

In case of Exist, you can ignore the case using the StringComparison enumeration, but that's not the case for Contains , where you need to take care of the case, or else you need custom IComparer to ignore the case