这是根据数据库值在C＃高亮列表框中将字符串传递给List的更好方法

Question

I would appreciate if someone can tell me what is the better way of defining list and passing a string to it

I am not sure which one to use or which one is better from performance point of view

var selection = "28,2,10,30,100,51";
List<string> categories = selection.Split(',').ToList();
List<string> categories = new List<string>(selection.Split(',')); 

I actually want to highlight the Listbox items based on database selection

after creating my list i loop through them & use following code to highlight the selection in the multi-selection list-box in asp.net

foreach (ListItem item in lstCatID.Items)
{
    if (categories.Contains(item.Value))
        item.Selected = true;
}

Is the the best way to do it or it can be done in any other way to enhance performance.

Answer 1

ToList internally calls the List constructor taking an argument of type IEnumerable so for both of your cases it would be same.

You should see: Reimplementing LINQ to Objects: Part 20 - ToList (Jon Skeet)

You may be wondering why we even need ToList, if we could just create a list by calling the constructor directly. The difference is that in order to call a constructor, you need to specify the element type as the type argument.

It would be better for you if you can time them both using Stopwtach to see the difference, Also first make sure your code works and then worry about the performance. Usually performance optmization for this kind of task results in negligible improvements.

Answer 2

If you are just using it to read value try using IEnumerable<string> instead if List<string> which is lighter and restrictive than list. When you use IEnumerable, you give the compiler a chance to defer work until later, possibly optimizing along the way. SO while using Linq expressions like contains that you are using here IEnumerable probably is the best bet. Apart from this many a times during desin pattern when you want to transfer list of items between 2 objects again IEnumerable is a best bet since it is more restrictive.

var selection = "28,2,10,30,100,51";          
IEnumerable<string> categories = selection.Split(',');

foreach (ListItem item in lstCatID.Items)
{
  if (categories.Contains(item.Value))
     item.Selected = true;
}