创建带有参数的委托函数

Question

I have the following delegate function in a Unit Test, and it works great

List<Record> RecordSet = FileData.RecordSet;
Record result = RecordSet.Find(
        delegate(Record r)
        {
            return r.UserID == "12345";
        }
    );

and it works great. I need to perform this search multiple times, so I had tried to add it in a function I could call that took the UserID as a parameter, it's VERY similar, but for some reason, ALWAYS returns null.

public Record findRecord(List<Record> RecordSet, string UserID)
{
    Record result = RecordSet.Find(
        delegate(Record r)
        {
            return r.UserID.Trim() == UserID;
        }
    );

    return null;
}

I have also tried it by hard coding "12345" in as the UserID value, that also returns null. What's even stranger is that when I am in debug mode and I look at the values in the RecordSet, I do see the Record with the exact UserID. Yet for some reason, no results, yet the same code and the same data in the first function above returns a result just fine.

Also, FYI, I have fond the LINQ solution to the problem:

Record result = RecordSet.Where(x => x.UserID == "12345").Select(x => x).First();

But I am specifically looking for reasons why the delegate solution is failing

Answer 1

The problem is that your method always returns null , because of this line:

return null;

Replace it with this and you should have better luck:

return result;

However, you can simplify this with a lambda expression which takes a Record and returns a bool . Try this:

return RecordSet.Find(r => r.UserID.Trim() == UserID);