CODEWITHSUNDEEP
c#asp.netlinq
The Muffin Man
The Muffin Man

Reputation: 20004

Selecting ListBox values against a List

I have a list:

var _books = new List<int> {233,5,20};

And a ListBox with a lot of books (their value is an item id)

How do I take this working code:

var t = from ListItem n in lbBooks.Items 
                    where _books.Contains(int.Parse(n.Value)) 
                    select n;
            foreach(ListItem i in t)
            {
                i.Selected = true;
            }

and convert it to lambda:

lbBooks.Items.Cast<ListItem>()
                .Where(n => _books.Contains(int.Parse(n.Value)))
                .Select(n => n.Selected = true);

Upvotes: 0

Views: 2021

Answers (4)

NinjaNye
NinjaNye

Reputation: 7126

Your not far off, you need to return the whole object and set Selected to true. Something like:

lbBooks.Items.Cast<ListItem>()
                .Where(n => _books.Contains(int.Parse(n.Value)))
                .Select(n => SetSelected(n));

The above .Select can be shortend to .Select(SetSelected); if you prefer

private ListItem SetSelected(ListItem listItem)
{
    listItem.Selected = true;
    return listItem
}

Additionally to save casting you could utilise the SetSelected to handle your casting once you have just the records you want. Your query would then become:

lbBooks.Items.Where(n => _books.Contains(int.Parse(n.Value)))
             .Select(n => SetSelected(n));

private ListItem SetSelected(Item item)
{
    ListItem result = item as ListItem;
    result.Selected = true;
    return result;
}

Upvotes: 1

The Muffin Man
The Muffin Man

Reputation: 20004

Cast to .ToList() and use the `ForEach' operator as so:

lbBooks.Items.Cast<ListItem>()
             .Where(n => _books.Contains(int.Parse(n.Value)))
             .Select(n => n).ToList().ForEach(n=> n.Selected=true);

Upvotes: 0

svick
svick

Reputation: 244757

The best option? Don't. LINQ queries are supposed to be just that – queries. And queries aren't supposed to have side effects. Your approach using foreach is perfectly fine.

If you really wanted, you could create your own extension method ForEach(), similar to the one on List<T>, but I don't think that's a good idea.

Upvotes: 1

Magnus
Magnus

Reputation: 46909

There is no build in ForEach extension method. You can create your own, but I do not see any problem with the code you have.

Upvotes: 0

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