ForEach Extension Method for ListItemCollection

Question

I implemented an ExtensionMethod which basically works as ForEach-Loop, my Implementation looks like this:

public static void ForEach(this ListItemCollection collection, Action<ListItem> act )
{
    foreach (ListItem item in collection)
        act(item);
}

However, I'd like the method to stop looping after the first time a specific condition is met.

Here's how I currently use it:

ddlProcesses.Items.ForEach(item => item.Selected = item.Value == Request["Process"]?true:false);

The Problem with this is that there can only be one item inside the DropDownList which matches this requirement, but the loop is being finished anyway, what would be the least ugly way to solve this problem?

Thanks.

If you are not experimenting **ddlProcesses.Items.FindByValue(Request["Process"]).Selected = true;** would be the simplest thing to do — V4Vendetta, Apr 29 '11 at 10:52
@V4Vendetta: Sorry, no such task in OP's question. But in fact, he will need this later, i guess. But everything up to him :) — abatishchev, Apr 29 '11 at 11:01
@abatishchev Maybe he does or not still there is **ClearSelection()** which does the trick — V4Vendetta, Apr 29 '11 at 11:03

score 5 · Accepted Answer · answered Apr 29 '11 at 10:45

You can take a Func<ListItem, bool> instead of an Action<ListItem> and break the loop if it returns true:

public static void ForEach(this ListItemCollection collection,
    Func<ListItem, bool> func)
{
    foreach (ListItem item in collection) {
        if (func(item)) {
            break;
        }
    }
}

You can use it like this:

ddlProcesses.Items.ForEach(
    item => item.Selected = (item.Value == Request["Process"]));

score 2 · Answer 2 · edited Apr 29 '11 at 10:49

2

public static void ForEach(this ListItemCollection collection, Action<ListItem> act )
{
    foreach (ListItem item in collection)
    {
        act(item);
        if(condition) break;
    }
}

edited Apr 29 '11 at 10:49

abatishchev

98,240
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answered Apr 29 '11 at 10:47

Gabriel

1,435
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Where does condition come from? – Peter Lillevold Apr 29 '11 at 10:53
@abatischev this is from OP " I'd like the method to stop looping after the first time a specific condition is met." – Gabriel Apr 29 '11 at 10:54
@Peter the OP could place his condition there ... I've just wanted to let him know that you can stop a foreach loop with a break; – Gabriel Apr 29 '11 at 10:56

score 1 · Answer 3 · edited May 23 '17 at 12:12

1

First do this:

IEnumerable<ListItem> e = ddlProcesses.Items.OfType<ListItem>(); // or Cast<ListItem>()

to get generic collection.

Then use can roll your own, generic extension method:

public static void ForEach<T>(this IEnumerable<T> collection, Action<T> action)
{
    foreach (T item in collection) action(item);
}

public static void ForEach<T>(this IEnumerable<T> collection, Func<T> func)
{
    foreach (T item in collection) if (func(item)) return;
}

Anyway, cache lookup result:

var process = Request["Process"];

e.ForEach(i => i.Selected = i.Value == process);

edited May 23 '17 at 12:12

Community

1
1

answered Apr 29 '11 at 10:46

abatishchev

98,240
88
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433

e.ToList() results in copying the whole list into a new List instance before iterating. This may not be desirable. – Peter Lillevold Apr 29 '11 at 10:55

score 1 · Answer 4 · answered Apr 29 '11 at 11:16

Your requirements are not 100% clear. Do you need to process all items to set them to false except the only one which matches the condition or do you just want to find the with the right condition or do you want to apply a function until a condition is met?

Only do something to an item the first time the condition matches

public static void ApplyFirst(this ListItemCollection collection,
                      Action<ListItem> action, Func<ListItem, bool> predicate)
{
    foreach (ListItem item in collection) 
    {
       if (predicate(item))
       {
           action(item);
           return;
       }
    }
}

Do something to an item everytime a condition matches

public static void ApplyIf(this ListItemCollection collection,
                      Action<ListItem> action, Func<ListItem, bool> predicate)
{
    foreach (ListItem item in collection) 
    {
       if (predicate(item))
       {
           action(item);
       }
    }
}

Do something to all items until a condition matches

public static void ApplyUntil(this ListItemCollection collection,
                      Action<ListItem> action, Func<ListItem, bool> predicate)
{
    foreach (ListItem item in collection) 
    {
       action(item);
       if (predicate(item))
       {
           return;
       }
    }
}

ForEach Extension Method for ListItemCollection

4 Answers4

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