We've been trying to figure out how to compare two calendar dates in C# ASP.NET.
The problem we have is that when a customer uses the calendar, they can choose to set it back in time.
Example:
2015-09-23 to 2015-08-23 <- this is something we don't want, it is set back in time.
How do we check if the start date is later than the end date.
We have seen someone using CDate? Which we did not understand how to use this.
We have tried to just remove the "-" from a string, convert it to an int and then calculate if the answer is less than 0.
But this was a big workaround. Is there an official or better way to do this?
If any more information is needed, feel free to ask!
You can use the CompareValidator in ASP.Net
<asp:CompareValidator ID="myID" ControlToCompare="StartDate"
ControlToValidate="EndDate" Type="Date" Operator="GreaterThanEqual"
ErrorMessage="The dates are not correct." runat="server"></asp:CompareValidator>
or else
DateTime d1 = new DateTime(2015, 9, 1);
DateTime d2 = new DateTime(2015, 8, 2);
if (d1 < d2)
{
//error
}
Easy enough. I assume its only the date part you are interested in and not the time. The DateTime.CompareTo() method compares two dates and returns one of the following integer values:
-1 Less Than
0 Equal To
1 Greater Than
Using this and the Current Date we can easily tell if the given date is in the past. This method will take a date string, like the one provide in your example, and compare it to the current date (ignoring the time element) and return true if the given date is in the past, or false if it is equal to or greater than the current date.
private bool IsDateInThePast(string inputDate)
{
DateTime dt = DateTime.Parse(inputDate);
return dt.CompareTo(DateTime.Parse(DateTime.Now.ToShortDateString())) < 0;
}
Obviously, you might want to add some validation and/or exception handling to handle an invalid input string.
Related
I have a function which convert date to my formatdate and compare it to CurrentDate.
It worked well when I test it with date is a date in Octorber compare to today (16/10/2013)
But if date is a date in November, the value return is true which means date < currentdate. I dont know why, anyone can explain it to me ? Thanks so much.
function IsPast(date) {
var fullDate = new Date();
var twoDigitMonth = fullDate.getMonth() + 1 + "";
if (twoDigitMonth.length == 1) twoDigitMonth = "0" + twoDigitMonth;
var twoDigitDate = fullDate.getDate() + "";
if (twoDigitDate.length == 1) twoDigitDate = "0" + twoDigitDate;
var currentDate = twoDigitDate + "/" + twoDigitMonth + "/" + fullDate.getFullYear();
var startDate = $.fullCalendar.formatDate(date, 'dd/MM/yyyy');
if (startDate <= currentDate) {return true;}
return false;
}
If you are being passed a Date object (and that seems to be what you get), then you can simply do:
function isPast(date) {
return new Date() > date;
}
If date isn't a date object, convert it to one first.
Note that identifiers starting with a capital letter are, by convention, reserved for constructors.
Edit: When I first read your question, I saw that you were using day first dates and jumped to my conclusion without really taking in your code. I've taken a closer look, and it appears my initial conclusion is just a red herring. The real problem is that you are taking two dates, converting them both to strings, and then trying to compare them. That's just silly - it will only tell you which string comes first alphabetically. Even sillier, is that for one of the dates you manually construct the string, but for the other one, you use a date formatting function. Why wouldn't you just use the date formatting function for both dates?
RobG's answer is correct and should be accepted.
When I see the date "01/11/2013", I read it as January 11, 2013, whereas you read it as 1 November, 2013. See the predicament the JavaScript engine is in when it tries to parse that date?*
When parsing JavaScript dates, I like to use year first dates, as these are unambiguous as far as I know. Everybody interprets "2013/11/01" as 2013 November 1. Including every JavaScript Date implementation I've seen.
Change your date format to be unambiguous.
*Frankly, I'm surprised you are seeing that behavior. I would expect that your system would be configured to expect day first dates and that the JavaScript engine would use those settings to properly parse the date. But, I'm not that surprised.
I am trying to check if the selected month is already past.
if (Convert.ToDateTime(DDMonths.SelectedItem.Text).Month > DateTime.Now.Month)
{
//logic here if date is not in the past
}
DDMonths.SelectedItem.Text value is April
However I am getting the following Format exception error:
String was not recognized as a valid DateTime.
You can parse the month by name with the following:
DateTime.ParseExact(DDMonths.SelectedItem.Text, "MMMM", CultureInfo.CurrentCulture ).Month
However, you'd be better off making the Value of each element in DDMonths the integer value corresponding to the month instead, if possible.
Convert.ToDateTime cannot understand your date format, you need to use DateTime.ParseExact instead:
if(DateTime.ParseExact(DDMonths.SelectedItem.Text, "MMMM", CultureInfo.CurrentCulture).Month > DateTime.Now.Month) {
...
}
it means that your line
Convert.ToDateTime(DDMonths.SelectedItem.Text)
is giving you error. You should use
DateTime.ParseExact(DDMonths.SelectedItem.Text,"MMMM",CultureInfo.InvariantCulture);
So the Text of your DropDownList-Item is not convertible to DateTime with the current culture. So maybe you are showing the month-name (what i assume) or the error is more subtiel. You could use the ListItem.Value to store the datetime in a specific format, for example:
"yyyyMMdd" -> "20130726"
Then you can parse it in this way:
var dt = DateTime.ParseExact("20130726", "yyyyMMdd", CultureInfo.InvariantCulture);
If you want to allow the monthname:
dt = DateTime.ParseExact("July", "MMMM", CultureInfo.InvariantCulture);
Since you are just looking for the number of the month, why parse it to a DateTime at all? You can just get it from the DateTimeFormatInfo directly:
string input = "April";
var months = DateTimeFormatInfo.CurrentInfo.MonthNames;
var monthNumber = 1 + Array.FindIndex(months, x => x.Equals(input, StringComparison.CurrentCultureIgnoreCase));
if (monthNumber > DateTime.Now.Month)
{
// ...
}
Do think about what you want to do if it is currently April. Depending on what you are doing, you may want to compare using >=.
Also, if you are writing a desktop application, this code (and the others) are just fine. But if you are writing a web application and this code is running server-side, then you have two additional concerns:
The culture should match the input. You may need to use a different culture, or the InvariantCulture.
You are comparing to DateTime.Now - which will be in the server's time zone. So if a user in another part of the world uses this on the 1st of their new month while your server is still on the prior day, then your comparison will fail.
You should be using a ParseExact variant of DateTime
DateTime.ParseExact("April", "MMMM", CultureInfo.InvariantCulture).Month // outputs 4
you should also try using the Value (DDMonths.SelectedItem.Value) component and fill it as needed
The work I'm doing consists on finding out one's astral sign, so I put a dateTimePicker to select the date of birth, but now I'm not sure how I will get the data from that dateTimePicker to check which sign is it...
Like for example, from january first to february 14th you are this sign, from this to that you're... you know what I mean.
You are not concerned about the year. You just need the month and day values:
DateTimePicker dtp = new DateTimePicker();
int month = dtp.Value.Month;
int day = dtp.Value.Day;
Then, you can do if-else statements around the various astral signs:
if (month >= 3 && day >= 20 && month < 4 && day <21 )
{
return AstralSign.Aries;
}
else if (/* some other sign */)
{
// ...
}
You can create an enum for the signs as well:
enum AstralSign
{
...
Aries
...
}
There is no built-in functionality in DateTimePicker for achieving this. You will have to either go for if-else approach or a switch statement to find out which sign a particular date belongs to..
If your DateTimePicker was called dateTimePicker, you could do it like this:
DateTime pickedDate = new DateTime(dateTimePicker.Value.Year, dateTimePicker.Value.Month, dateTimePicker.Value.Day);
And then you could use pickedDate as you want.
There is nothing in built in for Zodiac signs , so i would recommend you building your own list for the Zodiac signs.
Comparing a date falls in which zodia part you can go along with DayOfYear part of the Datetime value selected in the DatePicker (dateTimePicker1.Value)
So 0 to 46 could be your first zodiac and compare this with the DayOfYear part and you will have your Zodiac sign (else year would be a problem while comparing DateTime objects)
The DateTimePicker has a property Value. This contains the selected date by the user.
If you like to get informed when the user made his selection, simply subscribe to the ValueChanged property.
Afterwards simply compare if the the given date falls within the range of any astral sign.
To get the astral sign i would built up a nested dictionary Dictionary<int, Dictionary<int, AstralSign>> which could then be access by
selectedSign = astralSigns[pickedDate.Month][pickedDate.Day];
Say I have these two DateTime objects:
var dt1 = new DateTime(1900,12,1,1,1,1);
var dt2 = new DateTime(1900, 12, 1, 1, 59, 1);
Obviously if I do DateTime.Compare(dt1,dt2) the method will return a value indicating they do not equal the same (because of the 59/minute component).
If I only want comparison with precision restricted to a certain value (i.e. same day - dont care about hours/minutes etc) is the best way to do this just to rebuild each datetime object?
I.e.
DateTime.Compare(new DateTime(dt1.Year,dt1.Month,dt1.Day,1,1,1),new DateTime(dt2.Year,dt2.Month,dt2.Day,1,1,1))
or is there a smarter way to do this?
There is already a built in function to get the Date from a DateTime, namely the Date property:
DateTime.Compare(dt1.Date,dt2.Date)
In theory you could compare year, month and day in that order instead of building a new DateTime, but since DateTime is a small struct building it is rather cheap, causes no heap allocations etc. And the code is much more readable.
If you just want the same date, just compare the Date properties:
dt1.Date == dt2.Date
If you need down to the same hour, or up to the same month, you need to use the constructors as you've shown.
The same day is easy - just use the Date property:
dt1.Date.CompareTo(dt2.Date)
For other granularities you would probably need to manually build different values though.
For the following code, I would expect result to equal 2, because the MSDN states that 'd' "Represents the day of the month as a number from 1 through 31. A single-digit day is formatted without a leading zero.".
DateTime myDate = new DateTime( 2009, 6, 4 );
string result = myDate.ToString( "d" );
However, result is actually equal to '6/4/2009' - which is the short-date format (which is also 'd'). I could use 'dd', but that adds a leading zero, which I don't want.
To indicate that this is a custom format specifier (in contrast to a standard format specifier), it must be two characters long. This can be accomplished by adding a space (which will show up in the output), or by including a percent sign before the single letter, like this:
string result = myDate.ToString("%d");
See documentation
Rather than using string formatting strings, how about using the Day property
DateTime myDate = new DateTime(2009,6,4)
int result = myDate.Day;
Or if you really needed the result in string format
string result = myDate.Day.ToString();
If you are looking to get a specific date part out of a date object rather than a formatted representation of the date, I prefer to use the properties (Day, Month, Year, DayOfWeek, etc.) It makes reading the code a bit easier (particularly if someone else is reading/maintaining it that doesn't have the various formatting codes memorized)