datepicker: Add support for passing IOS8601 strings to datepicker regardless of the DateAdapter

[mahmood-sajjadi]

Bug, feature request, or proposal:

Bug

What is the expected behavior?

Initial value in text field is empty string and Date picket required an input text field which means should accept empty string as not defined value, or is user want to remove value, should be able to remove text field value

What is the current behavior?

in master code
in this PR : 8bb54ca
in this file:
https://github.com/angular/material2/blob/master/src/lib/datepicker/datepicker-input.ts#L119

an empty string is not an acceptable value and it is raising the following error:
Datepicker: value not recognized as a date object by DateAdapter.

What are the steps to reproduce?

Just add
formControlName="birthdate"
to input field in datepicker and sround it by formGroup

this is plunker example:
http://plnkr.co/edit/bhswcOgSB36yqD6Yr8nF?p=preview

please open chrome console to see the warning an error

What is the use-case or motivation for changing an existing behavior?

Using datepicker in form group

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

angular 4.3.2
material 2.0.0-beta.8-5967f6e

Is there anything else we should know?

It was working fine before that PR becuse the condition was
if (!value)
which is working as expected with empty string

[mmalerba]

We no longer support setting the value of the datepicker to something that is not a Date object, such as a string. If you want the datepicker to start off empty just use null instead of '': http://plnkr.co/edit/2mvkFihkfvEeX2Yhkmuw?p=preview

[nicholasjativa]

@mmalerba what would be a solution, then, in an instance where we previously would get a Date string from somewhere (like Firebase) and we try to set the value of a datepicker using setValue(aDateString)? I guess its possible to do setValue(newDate(aDateString)), however, that wouldn't work when copying an entire object (from a backend) to a formGroup using setValue(anObj). Thanks.

[mmalerba]

@nicholasjativa Hmm interesting I had not considered that case. The reason I removed the ability to use strings is because it was possible to put locale-sensitive strings in your code, e.g. 1/2/2017. Currently you would have to transform the response object to change the fields to actual Date objects. I could maybe add back the ability to accept ISO 8601 strings only

[nicholasjativa]

@mmalerba a fix like that would be great.

[mmalerba]

Reopening this to track the fix discussed above

[johnrjj]

Allowing ISO 8601 strings by default would be extremely useful

[another-guy]

What is the official decision on whether ISO8601 based dates will or will not be supported?

At the moment, I have to use a custom DataAdapter that seems to do the job, but should I even focus on that or wait till next version of the angular/material2? Gist with the custom adapter, please feel free to review: https://gist.github.com/another-guy/adc2d9d731af7693fdbfab21b1e227a9#file-iso8601datestringadapter-ts

Personally, I believe that using Date as the first class object is not quite right for datepicker since it represents a DateTime object rather than Date only.

[mmalerba]

@another-guy I will add the ability to pass ISO8601 strings to the datepicker and have it convert them into the appropriate object to for the DateAdapter but there are no current plans to add a ISO8601DateAdapter