Friday, February 1, 2008

Using "DHTML Calendar" with ASP.NET AJAX

Yesterday I lost 2 hours of my life trying to find why AJAX client library function "Date.parseInvariant(value, format)" does not work.

This is a beautiful function allows us to convert strings into Date objects in javascript. It allows us to specify exact format of a string in .NET way.

For example:

Date.parseInvariant("01/12/2008", "dd/MM/yyyy") will return valid date pointing to 1st of December 2008, and

Date.parseInvariant("01/12/20081", "dd/MM/yyyy") will return null ! Yes this is wonderful feature - there is no NaN result, no crazy dates - everything right like in .NET(almost everything :) )


But the function did not work. I debugged the Ajax library script and found the problem on the line:

        var result = new Date();
        if (year === null) {
            year = result.getFullYear();
        if (month === null) {
            month = result.getMonth();
        if (date === null) {
            date = result.getDate();
                result.setFullYear(year, month, date);
                if (result.getDate() !== date) return null;
                if ((weekDay !== null) && (result.getDay() !== weekDay)) {
            return null;

After execution of line

result.setFullYear(year, month, date);

the result date was not equal to date we just assigned it!

After long searches and guesses I have found the following script block in javascript file used by "The DHTML Calendar" by :

Date.prototype.__msh_oldSetFullYear = Date.prototype.setFullYear;
Date.prototype.setFullYear = function(y) {
    var d = new Date(this);
    if (d.getMonth() != this.getMonth())


The "Object patch" patched too much. It replaced setFullYear standard Date javascript function with it's own, completely ignoring two additional parameters that are passed into it.


I solved it by removing the "patch" - commenting it out. It worked for me, as I tested no critical functionality was broken for simple calendar dates selection. You can try to remove/replace the "patch" with more care, I just want to point to this problem with this post.

And in the end I want to thank the team - the calendar is great control anyway. I like it and use in my personal projects. Just yesterday was a little angry about this issue :P.


Hope this helps.

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Anonymous said...

Very helpful, thanks !!!

Sune said...

Thanks. I was struggling with this problem myself.