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Is there a method in c# to check if a string is a valid hexadecimal number?

I wanted to add a manual hexadecimal input for a C# repository of mine, I had no way of verifying if the user's input was a legitimate ARGB hexadecimal value the user had entered into the textbox or if it was a garbage hexadecimal number. Does anyone have a potential solution to this?

You can just use regex:
string pattern = #"^0[xX][0-9a-f]{8}$";
string input = "0x1a2b3C";
Match m = Regex.Match(input, pattern, RegexOptions.IgnoreCase);
if (m.Success)
{...}

So, I did a very inefficient method, I started off by making a pastebin with every single valid ARGB hex code, I then wrote the following:
WebClient Checker = new WebClient();
string List = Checker.Downloadstring("https://pastebin.com/raw/link");//link would be the pastebin
string Input = this.TextBox.Text;
if (List.Contains(Input))
{
//submit write file code here
}
else
{
System.Windows.Messagebox.Show("The Input Was Not Valid! Please Input A Valid ARGB Code!", "Error!");
}
This method ended up working for me. It isn't recommended but does the job right.

Regex for string without spacial characters or spaces [duplicate]

How do I check a string to make sure it contains numbers, letters, or space only?

In C# this is simple:
private bool HasSpecialChars(string yourString)
{
return yourString.Any(ch => ! char.IsLetterOrDigit(ch));
}

The easiest way it to use a regular expression:
Regular Expression for alphanumeric and underscores
Using regular expressions in .net:
http://www.regular-expressions.info/dotnet.html
MSDN Regular Expression
Regex.IsMatch
var regexItem = new Regex("^[a-zA-Z0-9 ]*$");
if(regexItem.IsMatch(YOUR_STRING)){..}

string s = #"$KUH% I*$)OFNlkfn$";
var withoutSpecial = new string(s.Where(c => Char.IsLetterOrDigit(c)
|| Char.IsWhiteSpace(c)).ToArray());
if (s != withoutSpecial)
{
Console.WriteLine("String contains special chars");
}

Try this way.
public static bool hasSpecialChar(string input)
{
string specialChar = #"\|!#$%&/()=?»«#£§€{}.-;'<>_,";
foreach (var item in specialChar)
{
if (input.Contains(item)) return true;
}
return false;
}

String test_string = "tesintg#$234524##";
if (System.Text.RegularExpressions.Regex.IsMatch(test_string, "^[a-zA-Z0-9\x20]+$"))
{
// Good-to-go
}
An example can be found here: http://ideone.com/B1HxA

If the list of acceptable characters is pretty small, you can use a regular expression like this:
Regex.IsMatch(items, "[a-z0-9 ]+", RegexOptions.IgnoreCase);
The regular expression used here looks for any character from a-z and 0-9 including a space (what's inside the square brackets []), that there is one or more of these characters (the + sign--you can use a * for 0 or more). The final option tells the regex parser to ignore case.
This will fail on anything that is not a letter, number, or space. To add more characters to the blessed list, add it inside the square brackets.

Use the regular Expression below in to validate a string to make sure it contains numbers, letters, or space only:
[a-zA-Z0-9 ]

You could do it with a bool. I've been learning recently and found I could do it this way. In this example, I'm checking a user's input to the console:
using System;
using System.Linq;
namespace CheckStringContent
{
class Program
{
static void Main(string[] args)
{
//Get a password to check
Console.WriteLine("Please input a Password: ");
string userPassword = Console.ReadLine();
//Check the string
bool symbolCheck = userPassword.Any(p => !char.IsLetterOrDigit(p));
//Write results to console
Console.WriteLine($"Symbols are present: {symbolCheck}");
}
}
}
This returns 'True' if special chars (symbolCheck) are present in the string, and 'False' if not present.

A great way using C# and Linq here:
public static bool HasSpecialCharacter(this string s)
{
foreach (var c in s)
{
if(!char.IsLetterOrDigit(c))
{
return true;
}
}
return false;
}
And access it like this:
myString.HasSpecialCharacter();

private bool isMatch(string strValue,string specialChars)
{
return specialChars.Where(x => strValue.Contains(x)).Any();
}

Create a method and call it hasSpecialChar with one parameter
and use foreach to check every single character in the textbox, add as many characters as you want in the array, in my case i just used ) and ( to prevent sql injection .
public void hasSpecialChar(string input)
{
char[] specialChar = {'(',')'};
foreach (char item in specialChar)
{
if (input.Contains(item)) MessageBox.Show("it contains");
}
}
in your button click evenement or you click btn double time like that :
private void button1_Click(object sender, EventArgs e)
{
hasSpecialChar(textbox1.Text);
}

While there are many ways to skin this cat, I prefer to wrap such code into reusable extension methods that make it trivial to do going forward. When using extension methods, you can also avoid RegEx as it is slower than a direct character check. I like using the extensions in the Extensions.cs NuGet package. It makes this check as simple as:
Add the [https://www.nuget.org/packages/Extensions.cs][1] package to your project.
Add "using Extensions;" to the top of your code.
"smith23#".IsAlphaNumeric() will return False whereas "smith23".IsAlphaNumeric() will return True. By default the .IsAlphaNumeric() method ignores spaces, but it can also be overridden such that "smith 23".IsAlphaNumeric(false) will return False since the space is not considered part of the alphabet.
Every other check in the rest of the code is simply MyString.IsAlphaNumeric().

Based on #prmph's answer, it can be even more simplified (omitting the variable, using overload resolution):
yourString.Any(char.IsLetterOrDigit);

No special characters or empty string except hyphen
^[a-zA-Z0-9-]+$

C# strip out not needed data using REGEX or something different

So i'm trying to strip data from a string because I have in WPF a "preset" input which looks like __,___, now a user must input something like 30,589, but when a user just gives in 5 or 50, it needs to strip the rest (keeping the ,) to propperly make a float of the input value. The code that I have right now looks like this;
if (inp_km.Text == "__,___")
{
team_results.results[inp_tour_part.SelectedIndex].km =
float.Parse("00,000",
NumberStyles.AllowDecimalPoint,
CultureInfo.GetCultureInfo("nl-NL")); // Give the new value
}
else
{
team_results.results[inp_tour_part.SelectedIndex].km =
float.Parse(inp_km.Text,
NumberStyles.AllowDecimalPoint,
CultureInfo.GetCultureInfo("nl-NL")); // Give the new value
}
But this code just check wether the input is left blank or not... Could someone help me out?
Edit
So I've included a screen, this is the input lay-out a user gets;
Os you can see, the inputs are 'pre-filled', the content of such an input is a "string", so, let's say, I type into the first input just 5;
Then the value (retreived in C# by input_name.Text) is 5_:__, but that's a "wrong" value and you can't fill in such things, how could I check if there still is a : or _ in the input.
Also, the bottom input is the same, but then it needs to be filled in completely.

So you want to check either the input is in one of the two forms: 12,345 or 12:34.
This can be done using Regex very easily.
static void Main(string[] args)
{
var inputComma = "12,345";
var inputColon = "98:76";
Regex regexComma = new Regex(#"^\d{2},\d{3}$");
Regex regexColon = new Regex(#"^\d{2}:\d{2}$");
var matchComma = regexComma.Match(inputComma);
if (matchComma.Success)
{
Console.WriteLine(inputComma);
}
Console.WriteLine();
var matchColon = regexColon.Match(inputColon);
if (matchColon.Success)
{
Console.WriteLine(inputColon);
}
Console.ReadLine();
}
NOTE:
You haven't quite clarified the valid formats for your input. The above will evaluate to true strictly for 12,345 format if commas are present (i.e., two digits followed by a comma followed by three digits), and for colon, only numbers of the format 12:34 (two digits before and after the colon) only.
You might want to modify your Regex based on your exact criteria.

Replacing _x with string.empty using Regex.Replace

I have a string "region_2>0" where I want to replace _2 with string.empty using Regex.
My expression is ((_)[^_]*)\w(?=[\s=!><]) which in both Regulator and Expresso gives me _2. However, the code(c#):
Regex.Match(legacyExpression, "((_)[^_]*)\\w(?=[\\s=!><])").Value
gives me "_2>0", which also causes the replace to be wrong (It returns "region" since removing the whole "_2>0" instead of "_2". The result I want is "region>0". Shouldn't the code and the regex programs give the same results? And how can I get it to work?
(Note the string is not static, it could be in many different forms, but the rule is I want to replace the last _X in the string with string.empty.
Thanks!

I copied your code as is into the new project:
static void Main(string[] args)
{
var legacyExpression = "region_2>0";
var rex = Regex.Match(legacyExpression, "((_)[^_]*)\\w(?=[\\s=!><])").Value;
Console.WriteLine(rex);
Console.ReadKey();
}
The output is _2.

I think this could work
(_\d+)

Allow user to only input text?

how do I make a boolean statement to only allow text? I have this code for only allowing the user to input numbers but ca'nt figure out how to do text.
bool Dest = double.TryParse(this.xTripDestinationTextBox.Text, out Miles);
bool MilesGal = double.TryParse(this.xTripMpgTextBox.Text, out Mpg);
bool PriceGal = double.TryParse(this.xTripPricepgTextBox.Text, out Price);

Update: looking at your comment I would advise you to read this article:
User Input Validation in Windows Forms
Original answer: The simplest way, at least if you are using .NET 3.5, is to use LINQ:
bool isAllLetters = s.All(c => char.IsLetter(c));
In older .NET versions you can create a method to do this for you:
bool isAllLetters(string s)
{
foreach (char c in s)
{
if (!char.IsLetter(c))
{
return false;
}
}
return true;
}
You can also use a regular expression. If you want to allow any letter as defined in Unicode then you can use this regular expression:
bool isOnlyLetters = Regex.IsMatch(s, #"^\p{L}+$");
If you want to restrict to A-Z then you can use this:
bool isOnlyLetters = Regex.IsMatch(s, #"^[a-zA-Z]+$");

You can use following code in the KeyPress event:
if (!char.IsLetter(e.KeyChar)) {
e.Handled = true;
}

You can use regular expression, browse here: http://regexlib.com/

You can do one of a few things.
User Regular Expression to check that the string matches your concept of 'Text' only
Write some code that checks each character against a list of valid characters. Or even use char.IsLetter()
Use the MaskedTextBox and set a custom mask to limit input to text only characters

I found hooking up into the text changed event of a textbox and accepting/rejecting the changes an acceptable solution. To "only allow text" is a rather vague definition, but you may as well check if your newly added text (the next char) is a number or not and simply reject all numbers/disallowed characters. This will make users feel they can only enter characters and special characters (like dots, question marks etc.).
private void UTextBox_TextChanged(object sender, EventArgs e)
{
string lastCharacter = this.Text[this.Text.Length-1].ToString();
MatchCollection matches = Regex.Matches(lastCharacter, "[0-9]", RegexOptions.None);
if (matches.Count > 0) //character is a number, reject it.
{
this.Text = Text.Substring(0, Text.Length-1);
}
}