I need to know the timezone for a certain language which I get from the current culture info object.
I can not use 3rd party libs like nodatime.
What property of the CultureInfo.CurrentCulture is important when I enumerate through all system time zones and want to get the right timezone?
If all you've got is culture, that's basically some string like: MX (Spanish Mexico), es-CO (Spanish Columbia), and fr-CA (French Canada) then you just have to correspond each on of these to a timezone, except no such one to one relationship exists. So no. You can roughly know the timezone (as pointed out in comments), fr-CA is all in the same timezone, but MX is in four (MX isn't enough information to gauge timezone).
So you don't have enough data to know, what can you do. If you need to know their timezone on the server side try geo-location:
How can I find a user's GEO Location using ASP.NET?
However, if it's just the web page that needs to know, try putting that logic in the JavaScript which is executing on their machine.
Or you could just... ask them.
Related
I am storing all the DateTime fields as UTC time. When a user requests a web page, I would like to take his preferred local timezone (and not the local timezone of the server machine) and automatically display all the DateTime fields in all the web forms as local dates.
Of course, I could apply the conversion on every DateTime.ToString() call in every form or implement some helper utility but it is a time consuming task, and also there are some 3rd party components which are tricky to configure with custom DateTime display templates.
Essentially, I would like to make the DateTime class to behave as follows:
from this moment on for this web request,
whenever some code calls DateTime.ToString(), convert it to the local time
using the timezone offset given at the very beginning of the web request,
but if possible, please keep .NET core library DateTime.ToString() calls intact
(I don't want to mess up event logging timestamps etc.)
Is there any way to do it?
BTW, I am using ASP.NET MVC 4, if it matters.
You can't do directly what you asked for, but I will suggest some alternatives. As Nicholas pointed out, there is nothing in HTTP that would give you the time zone directly.
Option 1
First, decide which type of time zone data you want to work with. There are two different types available, either the Microsoft time zones that you can access with the TimeZoneInfo class, or the IANA/Olson time zones that the rest of the world uses. Read here for more info. My recommendation would be the latter, using the implementation provided by NodaTime.
Then determine which time zone you want to convert to. You should allow your user a setting somewhere to pick their time zone.
You might show a drop-down list to pick one of several time zones, or you might do something more useful, like display a map of the world that they can click to select their time zone. There are several libraries that can do this in Javascript, but my favorite is this one.
You might want to guess a default time zone to use, so you can be as close to accurate as possible before they pick from the list (or map). There is a great library for this called jsTimeZoneDetect. It will interrogate the browser's clock and make a best guess assumption of what time zone it might be. It is fairly good, but it is still just a guess. Don't use it blindly - but do use it to determine a starting point. Update You can now also do this with moment.tz.guess(), in the moment-timezone component of moment.js.
Now that you know the time zone of the user, you can use that value to convert your UTC DateTime values to that local time zone. Unfortunately, there is nothing you can set on the thread that will do that. When you change the system time zone, it is global for all processes and threads. So you have no choice but to pass the time zone to each and every place you are sending it back. (I believe this was your main question.) See this almost duplicate here.
Before you convert it to a string, you will need to also know the user's locale (which you can get from the Request.UserLanguages value). You can assign it to the current thread, or you can pass it as a parameter to the DateTime.ToString() method. This doesn't do any time zone conversion - it just makes sure that the numbers are in the correct position, using the correct separators, and the appropriate language for names of weekdays or months.
Option 2
Don't convert it to local time on the server at all.
Since you said you are working with UTC values, make sure their .Kind property is Utc. You should probably do this when you load from your database, but if you have to you can do it manually:
myDateTime = DateTime.SpecifyKind(myDateTime, DateTimeKind.Utc);
Send it back to the browser as pure UTC, in an invariant format like ISO8601. In other words:
myDateTime.ToString("o"); // example: "2013-05-02T21:01:26.0828604Z"
Use some JavaScript on the browser to parse it as UTC. It will automatically pick up the local time settings of the browser. One way is to use the built-in Date object in JavaScript, like this:
var dt = new Date('2013-05-02T21:01:26.0828604Z');
However, this will only work in newer browsers that support the ISO-8601 format. Instead, I recommend using the moment.js library. It is consistent across browsers, and it has better support for ISO dates, and localization. Plus you get a lot of other useful parsing and formatting functions.
// pass the value from your server
var m = moment('2013-05-02T21:01:26.0828604Z');
// use one of the formats supported by moment.js
// this is locale-specific "long date time" format.
var s = m.format('LLLL');
The advantage of Option 1 is that you can work with times in any time zone. If you can ask the user for their timezone from a dropdown list, then you need not use any Javascript.
The advantage of Option 2 is that you get the browser to do some of the work for you. This is the best way to go if you're sending out raw data, such as making AJAX calls to a WebAPI. However, JavaScript is only aware of UTC and the browser's local time zone. So it doesn't work so well if you need to convert to other zones.
You should also be aware that if you choose Option #2, you may be affected by a flaw in the design of ECMAScript 5.1. This comes into play if you are working with dates that are covered by a different set of daylight saving time rules than are currently in effect. You can read more in this question, and on my blog.
It would be so much easier if we had some time zone information in the HTTP headers, but unfortunately we don't. These are a lot of hoops to jump through, but it's the best way to have both flexibility and accuracy.
The short answer is that you can't. HTTP doesn't require (or even provide a standard way) for the user agent (browser) to provide local time or timezone information in the HTTP request.
You either need to
ask the user for their preferred time zone, or
have client-side javascript report it to you somehow (cookie? ajax? other?)
Bear in mind that a client-side javascript solution isn't perfect, either. Javascript disabled (or non-existent, for some browsers). Javascript might not have access to timezone information. Etc.
I am storing all the DateTime fields as UTC time. When a user requests a web page, I would like to take his preferred local timezone (and not the local timezone of the server machine) and automatically display all the DateTime fields in all the web forms as local dates.
Of course, I could apply the conversion on every DateTime.ToString() call in every form or implement some helper utility but it is a time consuming task, and also there are some 3rd party components which are tricky to configure with custom DateTime display templates.
Essentially, I would like to make the DateTime class to behave as follows:
from this moment on for this web request,
whenever some code calls DateTime.ToString(), convert it to the local time
using the timezone offset given at the very beginning of the web request,
but if possible, please keep .NET core library DateTime.ToString() calls intact
(I don't want to mess up event logging timestamps etc.)
Is there any way to do it?
BTW, I am using ASP.NET MVC 4, if it matters.
You can't do directly what you asked for, but I will suggest some alternatives. As Nicholas pointed out, there is nothing in HTTP that would give you the time zone directly.
Option 1
First, decide which type of time zone data you want to work with. There are two different types available, either the Microsoft time zones that you can access with the TimeZoneInfo class, or the IANA/Olson time zones that the rest of the world uses. Read here for more info. My recommendation would be the latter, using the implementation provided by NodaTime.
Then determine which time zone you want to convert to. You should allow your user a setting somewhere to pick their time zone.
You might show a drop-down list to pick one of several time zones, or you might do something more useful, like display a map of the world that they can click to select their time zone. There are several libraries that can do this in Javascript, but my favorite is this one.
You might want to guess a default time zone to use, so you can be as close to accurate as possible before they pick from the list (or map). There is a great library for this called jsTimeZoneDetect. It will interrogate the browser's clock and make a best guess assumption of what time zone it might be. It is fairly good, but it is still just a guess. Don't use it blindly - but do use it to determine a starting point. Update You can now also do this with moment.tz.guess(), in the moment-timezone component of moment.js.
Now that you know the time zone of the user, you can use that value to convert your UTC DateTime values to that local time zone. Unfortunately, there is nothing you can set on the thread that will do that. When you change the system time zone, it is global for all processes and threads. So you have no choice but to pass the time zone to each and every place you are sending it back. (I believe this was your main question.) See this almost duplicate here.
Before you convert it to a string, you will need to also know the user's locale (which you can get from the Request.UserLanguages value). You can assign it to the current thread, or you can pass it as a parameter to the DateTime.ToString() method. This doesn't do any time zone conversion - it just makes sure that the numbers are in the correct position, using the correct separators, and the appropriate language for names of weekdays or months.
Option 2
Don't convert it to local time on the server at all.
Since you said you are working with UTC values, make sure their .Kind property is Utc. You should probably do this when you load from your database, but if you have to you can do it manually:
myDateTime = DateTime.SpecifyKind(myDateTime, DateTimeKind.Utc);
Send it back to the browser as pure UTC, in an invariant format like ISO8601. In other words:
myDateTime.ToString("o"); // example: "2013-05-02T21:01:26.0828604Z"
Use some JavaScript on the browser to parse it as UTC. It will automatically pick up the local time settings of the browser. One way is to use the built-in Date object in JavaScript, like this:
var dt = new Date('2013-05-02T21:01:26.0828604Z');
However, this will only work in newer browsers that support the ISO-8601 format. Instead, I recommend using the moment.js library. It is consistent across browsers, and it has better support for ISO dates, and localization. Plus you get a lot of other useful parsing and formatting functions.
// pass the value from your server
var m = moment('2013-05-02T21:01:26.0828604Z');
// use one of the formats supported by moment.js
// this is locale-specific "long date time" format.
var s = m.format('LLLL');
The advantage of Option 1 is that you can work with times in any time zone. If you can ask the user for their timezone from a dropdown list, then you need not use any Javascript.
The advantage of Option 2 is that you get the browser to do some of the work for you. This is the best way to go if you're sending out raw data, such as making AJAX calls to a WebAPI. However, JavaScript is only aware of UTC and the browser's local time zone. So it doesn't work so well if you need to convert to other zones.
You should also be aware that if you choose Option #2, you may be affected by a flaw in the design of ECMAScript 5.1. This comes into play if you are working with dates that are covered by a different set of daylight saving time rules than are currently in effect. You can read more in this question, and on my blog.
It would be so much easier if we had some time zone information in the HTTP headers, but unfortunately we don't. These are a lot of hoops to jump through, but it's the best way to have both flexibility and accuracy.
The short answer is that you can't. HTTP doesn't require (or even provide a standard way) for the user agent (browser) to provide local time or timezone information in the HTTP request.
You either need to
ask the user for their preferred time zone, or
have client-side javascript report it to you somehow (cookie? ajax? other?)
Bear in mind that a client-side javascript solution isn't perfect, either. Javascript disabled (or non-existent, for some browsers). Javascript might not have access to timezone information. Etc.
Like DateTime.Now gives us current date and time with respect to current system.
How can we find Current Time of different culture i.e different timezone using c# asp.net???
I find SystemTimeToTzSpecificLocalTime Function but how can i used this one???
If you're using .NET 3.5 or later, you can use TimeZoneInfo:
TimeZoneInfo otherZone = ...;
DateTime otherZoneTimeNow = TimeZoneInfo.ConvertTime(DateTime.UtcNow, otherZone);
You need to be somewhat careful using TimeZoneInfo - different DateTime "kinds" do different things - you should read the docs for any call you make carefully. (I recently blogged about the problems with DateTime... TimeZoneInfo basically has to handle the ambiguity.)
You can use a service, like the Yahoo! Web Services API, to pull this information and more. You can get time zone, local time, population, etc. with the Yahoo! Web Services API. The biggest drawback to that approach is the maximum daily hit count.
You can check out this link for more details:
http://developer.yahoo.com/flash/maps/classreference/com/yahoo/maps/webservices/geocoder/GeocoderResult.html
From what I have researched it is not possible to change the Timezone of a thread. So my question is why can't you?
I would have thought switching your application's culture to a specific country would also switch this, seems like expected behaviour IMO.
Edit
After revising I can see the reason why it probably shouldn't be mapped 1:1 by default. However, I still feel it would be a nice feature to be able to change the Timezone per thread.
They aren't a 1:1 so they're not really connected. If you set the current culture to en-US, which timezone is that? :)
Several countries have more than 1 timezone, so setting the culture (which is not country specific either for that matter), doesn't really have much to do with the timzone.
Culture is one thing, time zone is another. Suppose you're a South African citizen working in New York, USA. Obviously you want your time zone to be EST (GMT -5), since that's where you are; from what you're suggesting, however, then if you also set your culture to "af-ZA," as you might want to, doing so would automatically change your time zone to GMT +2.
I have used PInvoke to change the TimeZone of my Clients System. Instead of that Iwould like to change TimeZone of my Application only. Is there a workaround for this.
Can you simply store the timezone information in memory? You should be able to also serialize this data so that it is persisted between application executions.
This way, your application can exist in a timezone entirely of your choosing, independent of your machine's time (and location).
The TimeZone class should be a good starting point for what you need to do.
No, this is not possible. The time zone setting is system-wide. .NET does not provide any way to change the local time zone on a per-application basis.