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Displaying phone format XAML/c#

In my windows phone project, I would like the user to enter his phone number in xxx-xxx-xxxx format. The country code it not required. I tried to implement regex, but i am not getting it right. I just want it to be displayed to the user as he enters it, nothing more, nothing less. This is what I have used
^\(\d{3}\) ?\d{3}( |-)?\d{4}$
But no matter what i put in, I always get this error (in this case 5) "Unrecognized escape sequence". I noticed, this is only with reference to the oblique. When I add a "" after it, the error goes away, but I do not get what I want. Is there a special way to input numbers in the textbox in than manner, on the XAML level?
Thanks in advance!

Put your regex inside verbatim string and also put the space, hyphen inside a group and make it as optional.
#"^\(\d{3}\)([- ]?)\d{3}\1\d{4}$"
DEMO

For testing your RegEx you can use this site: http://www.regexlib.com/RETester.aspx?AspxAutoDetectCookieSupport=1.
For your xxx-xxx-xxxx format I would use it:^\d{3}-?\d{3}-?\d{4}$

Optimistic RegEx Matching for User Text Entry

I'm working on a text entry application that uses regular expressions to validate user input. The goal is to allow keypresses that fit a certain RegEx while rejecting invalid characters. One issue I've run into is that when a user starts inputting information they may create a string that doesn't yet match the given regex, but could cause a match in the future. These strings get erroneously rejected. Here's an example - given the following regex for inputting date information:
(0?[1-9]|10|11|12)/(0?[1-9]|[12]\\d|30|31)/\\d{2}\\d{2}
A user may begin entering "1/" which could be a valid date, but RegEx.IsMatch() will return false and my code ends up rejecting the string. Is there a way to "optimistically" test strings against a regular expression so that possible or partial matches are allowed?
Bonus: For this RegEx in particular there are some sequences which cause required characters. For example, if the user types "2/15" the only possible valid character they could enter next is "/". Is it possible to detect those scenarios so that the required characters could be automatically entered for the user to ease input?

What you can do is anchor your RegExp (i.e. adding ^ and $, as in start/end of line) and make some component optionnal for validation, but strictly defined if present.
Something looking like this:
^(0?[1-9]|10|11|12)(/((0?[1-9]|[12]\\d|30|31)(/(\\d{2}(\\d{2})?)?)?)?)?$
I do realize it looks horrible but as far as I know there is no way to tell the regexp engine to validate as long as the string satisfies the beginning of the regexp pattern.
In my opinion, the best way to achieve what you want to do is to create separate inputs for day/month/date and check their value when leaving the text field.
It also provides a better visibility and user-experience, as I believe no one likes to be prevented from typing certain characters into a text field with or without noticing them disappear as they type or having slashes inserted automatically and without notice.

Have you ever used and app or form that worked that way, simply refusing to accept any keypress it didn't like? If the answer is Yes, did it blow an electronic raspberry each time you pressed a wrong key?
If you really need to validate the input before the form is submitted, use a passive feedback mechanism like a red border around the textfield that disappears the regex matches the input. Also, make sure there's a Help button or a tooltip nearby to provide constructive feedback.
Of course, the best option would be to use a dedicated control like a date-entry widget. But whatever you do, don't do it in such a a way that it feels like you're playing guessing games with the user.

Character / Language

I just developed a simple asp.net mvc application project for English only. I want to block user's any input for a language other than English. Is it possible to know whether user inputs other languages when they write something on textbox or editor in order to give a popup message?

You could limit the input box to latin characters, but there's no automatic way to see if the user entered something in say English, Finnish or Norwegian. They all mostly use a-z. Any character outside of a-z could give you an indication, but certain accents needs to be allowed in English as well, so it's not 100%.
Google Translate exposes a javascript API to detect the language of text.

Use the following code:
<p>Note that this community uses the English language exclusively, so please be
considerate and write your posts in English. Thank you!</p>

there are two tests you can do. one is to find out what the cultureinfo is set on the users machine:
http://msdn.microsoft.com/en-us/library/system.threading.thread.currentuiculture.aspx
this will give you their current culture setting, which is a start. of course, you can have your setting as 'english' but still typing in russian, and most of the letters will be the same..
so the next step is to discover the language using this: http://www.google.com/uds/samples/language/detect.html
it's not the greatest, according to online discussions, but its a place to start. I'm sure there are better natural language identifiers out there, though.

Checking for Latin 26
If you wanted to ensure that any non-English letters were submitted, you could simply validate that they fall outside the A-Z, a-z, 0-9 and normal punctuation ranges. It sounds like you want the regular non-Latin characters to be detected and rejected.
Detecting the user's OS settings, keyboard settings isn't the best way, as the user could have multiple keyboards attached, and have use of copy/paste.
UI Validation
At the user interface level, you could create a jQuery method that would check the value of a textbox for a value other than your acceptable range. Perhaps that's A-Z, a-z and numeric. You could do this on event onBlur. Remember that you might want to allow ', .
$('#customerName').blur(function() {
var isAlphaNumeric;
//implementation of checking a-z, A-Z, 0-9, etc.
alert(isAlphaNumeric);
});
Controller Validation
If you wanted to ALSO implement this at the controller level, you could run a regex on the incoming values.
public ActionMethod CreateCustomer(string custName)
{
if (IsAcceptableRange(custName))
{
//continue
}
}
public bool IsAcceptableRange(string input)
{
//whitelist all the valid inputs here. be sure to include
//space, period, apostrophe, hypen, etc
Regex alphaNumericPattern=new Regex("[^a-zA-Z0-9]");
return !alphaNumericPattern.IsMatch(input);
}

Google Translate was quoted in two answers, but I want to add that Microsoft Word API may also be used to detect language, just like Word does for check spelling.
It is for sure not the best solution, since language detection by Microsoft Office doesn't work very well (IMHO), but may be an alternative if doing web requests to Google or other remote service on every posted message is not a solution.
Also, check spelling through Microsoft Word API can be useful too. If a message has a huge number of misspelled words when checking in English, it's probably because the message is written in another language (or the author of the message writes too badly, too).
Finally, I completely agree with Matti Virkkunen. The best, and maybe the only way to ensure that messages will be written in English is to ask the users to write in English. Otherwise, it's just as bad as implementing obscenity filters.

Verifying that an uploaded file contains only plain text

I have an ASP.NET MVC application that allows the user to upload a file that should only contain plain text.
I am looking for a simple approach to validate that the file does indeed contain only text.
For my purposes I am happy to define text as any of the characters that I can see printed on my GB QWERTY keyboard.
Business rules mean that my uploaded file won't contain any accented characters, so it doesn't matter if the code accepts or rejects these.
Approaches so far that have not worked:
Checking the content-type; no good as this is dependant on the file extension
Checking char.IsControl for each character; no good as the file can contain pipe (|) characters which are considered to be control characters
I'd rather avoid using a lengthy Regex pattern to get this to work.

It sounds like you want ASCII characters 32-126 plus a few odds and ends like 9 (horizontal tab), carriage return & linefeed, etc..
I'd rather avoid using a lengthy Regex
pattern to get this to work.
As long as that doesn't mean 'no regular expressions at all', you can use the accepted answer from this stack overflow question (I've added the horizontal tab character to the original):
^([^\x09\x0d\x0a\x20-\x7e\t]*)$

Regular expression to define format of backup filenames

In the application I am currently working on, I have an option to create automatic backups of a certain file on the hard disk. What I would like to do is offer the user the possibility to configure the name of the file and its extension.
For example, the backup filename could be something like : "backup_month_year_username.bak". I had the idea to save the format in the form of a regular expression. For the example above, the regexp would look like :
"^backup_(?<Month>\d{2})_(?<Year>\d{2})_(?<Username>\w).(?<extension>bak)$"
I thought about using regex because I will also have to browse through the directory of backuped files to delete those older than a certain date. The main trouble I have now is how to create a filename using the regex. In a way I should replace the tags with the information. I could do that using regex.replace and another regex, but I feel it's a big weird doing that and it might be a better way.
Thanks
[Edit] Maybe I wasn't really clear in the first go, but the idea is of course that the user (in this case an admin that will know regex syntax) will have the possibility to modify the form of the filename, that's all the idea behind it[/Edit]

... and if the regex changes, it is next to impossible to reconstruct a string from a given regex.
Edit:
Create some predefined "place-holders": %u could be the user's name, %y could be the year, etc.:
backup_%m_%y_%u.bak
and then simple replace the %? with their actual values.

It sounds like you're trying to use the regular expression to create the file name from a pattern which the user should be able to specify.
Regular expressions can - AFAIK - not be used to create output, but only to validate input, so you'd have the user specify two things:
a file name production pattern like Bart suggested
a validation pattern in form of a regular expression that helps you split the file names into their parts
EDIT
By the way, your sample regex contains an error: The "." is use for "any character", also \w only matches one word character, so I guess you meant to write
"^backup_(?<Month>\d{2})_(?<Year>\d{2})_(?<Username>\w+)\.(?<extension>bak)$"

If the filename is always in this form, there is no reason for a regex, as it's easier to process with string.Split ...

With Bart's solution it is easy enough to split (using string.Split) the generated file name using underscore as the delimiter, to get back the information.

Ok, I think I have found a way to use only the regex. As I am using groups to get the information, I will use another regular expression to match the regular expression and replace the groups with the value:
Regex rgx = new Regex("\(\?\<Month\>.+?\)");
rgx.Replace("^backup_(?<Month>\d{2})_(?<Year>\d{2})_(?<Username>\w+)\.(?<extension>bak)$"
, DateTime.Now.Month.ToString());
Ok, it's really a hack, but at least it works and I have only one pattern defined by the user. It might not work if the regex is too complex, but I think I can deal with that problem.
What do you think?