Generic List Find using lambda expression in c#

Question

I have this code:

List<Visibility> ListVisibility = new List<Visibility>();
    public class Visibility
    {
        public int ShpNo;
        public int QtyShp;
        public int NumPallets;
        public string ETA;            
    }

Visibility item = ListVisibility.Find(VisibItem => VisibItem.ETA == e.Day.Date.ToShortDateString());

But the above Find is not returning any Item, when there is an item that matches that condition.

What could be wrong here?

Are you sure there is a match for the exact string returned by ToShortDateString? — user27414
– user27414, Commented Nov 28, 2012 at 17:39
If you can refactor to use a DateTime for ETA instead of a string, comparisons will be easier. — user27414
– user27414, Commented Nov 28, 2012 at 17:40

Alexei Levenkov · Accepted Answer · 2012-11-28 17:46:26Z

4

Most likely string match does not find a match. Change code to compare dates as Date portions of DateTime and it will have better chance to work.

item => DateTime.Parse(item.ETA).Date == e.Day.Date

Sample is assuming e.Day is DateTime. Also you may need to handle "item.ETA is not valid date/empty" case (i.e. by using DateTime.TryParse) to match original behavior.

edited Nov 28, 2012 at 17:46

answered Nov 28, 2012 at 17:40

Alexei Levenkov

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Comments

user7116 · Accepted Answer · 2012-11-28 17:41:49Z

2

Any number of things come to mind, but two that seem most likely:

Is the string in Visibility.ETA trimmed of leading and trailing whitespace?
Does the case of the string in Visibility.ETA match that of DateTime.ToShortDateString()?

If you change your condition to:

var date = e.Day.Date.ToShortDateString();
var vis = list.Find(
    v => String.Compare(v.ETA, date, StringComparison.OrdinalIgnoreCase) == 0);

Does it find the item you're looking for? If not you should consider whether or not you need to convert ETA to a DateTime.

answered Nov 28, 2012 at 17:41

user7116

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Comments

Preston Guillot · Accepted Answer · 2012-11-28 17:51:36Z

1

Occam's razor: Your assumption that there is an item that matches your condition is incorrect.

You can verify that the method works with a simple test (this uses NUnit).

[Test]
public void TestFind()
{
     var etaValue = DateTime.Now.Date.ToShortDateString();
     var visibilities = new List<Visibility> { new Visibility { ETA = etaValue } };
     var foundItem = visibilities.Find(x => x.ETA == etaValue);
     Assert.That(foundItem, Is.Not.Null);
}

answered Nov 28, 2012 at 17:51

Preston Guillot

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