C# 即使列表为空，列表计数也始终返回 1

Question

I'm trying to debug a method in C# but my basic syntax skills here seem to be lacking. The method accepts a list of dates as a comma-separated text string, This string is converted to a list. then processed, However, it seems that even when an empty string is passed to the method. it still outputs 1 when the list is counted.

The code is as follows:

public static int DaysLeft(DateTime endDate, DateTime startDate, Boolean excludeWeekends, String excludeDates)
    {
        int counter = 0;

        List<string> excludeDatesList = new List<string>(excludeDates.Split(','));

        counter = excludeDatesList.Count;

        return counter;
    }

If I pass an empty string in as the excludeDates parameter, it returns 1. If I pass a single date it returns 1. If I pass two dates, it returns 2 etc. So it's kind of working except where there's nothing passed in, when I'd expect it to return 0 but it actually returns 1.

Can anyone point me in the right direction?

Thanks

Answer 1

Even for an empty string, Split will return that string in the array, so the list will be created with... one empty string, producing a .Count of 1. [ Edit : You can call excludeDates.Split(',', StringSplitOption.RemoveEmptyEntries) so that it doesn't.]

To make your function behave as you expect, you should probably try to parse each "date" string returned from Split() , and only increment the counter for valid dates.

Something like this:

    int counter = 0;
    var possibleDates = excludeDates.Split(',');

    foreach (var dateStr in possibleDates)
    {
        // Right now it just counts "good" dates, though could also do something
        //  with each date as well
        DateTime dt;
        if (DateTime.TryParse(dateStr, out dt))
            counter++;
    }

    return counter;

If you're looking for the simplest way, you should just check the parameter to see if it's the empty string, and return 0 in that case:

if (string.IsNullOrEmpty(excludeDates))
    return 0;

Answer 2

Splitting on the character is returning an empty element.

Try using excludeDates.Split(',', StringSplitOptions.RemoveEmptyEntries) instead.

Answer 3

You can use the remove empty entries option.

var blah = "";

var split = blah.Split(new[]{';'}, StringSplitOptions.RemoveEmptyEntries);
var split2 = blah.Split(new[]{';'});

// Returns zero
Console.WriteLine(split.Length);

// Returns one
Console.WriteLine(split2.Length);

Answer 4

That is normal behavior. When there is nothing to split it will return a list with the string itself as the first element which counts as one.

Answer 5

The array returned by String.Split() always has one element in it, even if it is the empty string.

Answer 6

Inserting an empty string into the list will create a list of one element. That element would be your empty string.

Answer 7

The result of calling string.Split on a string that doesn't contain the delimiter (in this case, a comma), is an array containing a single element, namely the original string. This also happens if the string is empty.

The solution is to specify Split to omit empty entries:

List<string> excluseDatesList = new List<string>(excludeDates.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries));

Answer 8

As dlev said.. but to add an example to illustrate, if you pass in the string "," - which is just a comma, then ",".Split(',').Count() will return 2. for ",,,," which is just four commas, you will get back 5 for the count...

Answer 9

if you look at the Split method, it has the following logic:

int num = this.MakeSeparatorList(separator, ref sepList);
if (num == 0 || count == 1)
{
    return new string[]
    {
        this
    };
}

Therefore, even if the string is an empty string it will return a single item in the array.