如何填充列表 <String> 使用Winforms中的Listbox控件中已存在的值

Question

I have a listbox which has a couple of values and is already populated (from user input). Later in my program I want to take these values from the listbox and populate them to a List collection.

One of the approach is of course to iterate through the items of the listbox and populate the List collection one by one (in a loop) using Add method.

But is there a better more efficient way to do this in one shot meaning all the items of the listbox get copied over to a List collection.

I also looked at the AddRange method but that doesnt seem to help.

Any suggestions for this?

Answer 1

It's not necessarily more efficient (in terms of speed/memory), but you can save some typing via LINQ:

List<string> items = listBox.Items.Cast<object>()
                            .Select(item => item.ToString()).ToList();

Answer 2

If it must be a List<string> , I think you will have to enumerate the items and add them to a list (since you are concerned about the efficiency of LINQ). If you can use a string[] , you could use the CopyTo method:

string[] destination = new string[listBox1.Items.Count];
listBox1.Items.CopyTo(destination, 0);

Answer 3

No there isn't a more efficient way.

If anything existed it would simply abstract away what you will be doing anyways via an extension method or other means and could have the possibility of making your code less readable.

The CopyTo method does exist via the ObjectCollection on the Items property which could then be LINQ'ed to a List<T> .

        ListBox lb = new ListBox();
        object[] items = new object[lb.Items.Count];
        lb.Items.CopyTo(items, 0);

Answer 4

The ItemCollection class implements IList , you'll need to cast the items in the collection to String since it's not a generic collection, but you already have a "List collection" of the items.

If you really need a copy of the items in collection then no, there isn't going to be a more efficient way. There are plenty of ways to implement syntatic sugar so that the code is more concise, but ultimately they will all be iterating over the items and creating copies to be added to a new collection.

Answer 5

This seems to be a duplicate of: Most succinct way to convert ListBox.items to a generic list

If you're copying from the listbox, what is populating that list? It might be a better option to go about it that way, versus taking 200k items and moving it over. if you're taking all items in a listbox, populate the List at the same time.

On that note.. really? 200k items in a listbox?. That right there seems a little over the top in a real world application.

Foreach(...) loops are very expensive - even when compiled into IL: http://diditwith.net/2006/10/05/PerformanceOfForeachVsListForEach.aspx

If you are unable to work with LINQ (your using <= VS 2005), this is one of the easier methods of doing it.

    string[] items = new string[listBox1.Items.Count];
    listBox1.Items.CopyTo(items, 0);
    List<string> list = new List<string>(items);

Answer 6

@Aaron McIver, your own method is a bit faster in my opinion. See this link for some performance testing I have done.