How to make textbox to accept only hexadecimal values

Question

1.40/5 (2 votes)

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hi,
i have a textbox on form and i want to make the textbox to accept only hexadecimal values,which means values from 0 to 9 and a to f.
how to do it.please help me.

What I have tried:

i have tried using [a-zA-Z] regularexpressions.it was unable

Posted 9-Aug-16 23:52pm

Member 12659926

Updated 10-Aug-16 4:54am

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3 solutions

Solution 1

C#

private void TextBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
	if (IsHexadecimal(Strings.Chr(e.KeyValue)) == false && e.KeyCode != Keys.Back) {
		e.Handled = true;
		e.SuppressKeyPress = true;
	}
}

public bool IsHexadecimal(string strInput)
{

	System.Text.RegularExpressions.Regex myRegex = new System.Text.RegularExpressions.Regex("^[a-fA-F0-9]+$");
	//boolean variable to hold the status
	bool isValid = false;
	if (string.IsNullOrEmpty(strInput)) {
		isValid = false;
	} else {
		isValid = myRegex.IsMatch(strInput);
	}
	//return the results
	return isValid;
}

private void TextBox1_TextChanged(object sender, System.EventArgs e)
{
	if (IsHexadecimal(TextBox1.Text) == false && string.IsNullOrWhiteSpace(TextBox1.Text) == false) {
		TextBox1.Clear();
		MessageBox.Show("Invalid Content");
	}
}

Posted 10-Aug-16 0:13am

CHANDRA SEKHARA GUPTA

Comments

charmyvora 10-Aug-16 6:30am

System.Text.RegularExpressions.Regex myRegex = new System.Text.RegularExpressions.Regex("^[a-fA-F0-9]+$");
string text = textBox1.Text;
bool isHex = myRegex.IsMatch(text);
if (!isHex)
{
textBox1.Text = text.Substring(0, text.Length - 1);
textBox1.SelectionStart = textBox1.Text.Length;
}

Member 12659926 10-Aug-16 6:39am

if I delete the text in textbox it was giving exception saying that length cannot be zero,wat to do for this

charmyvora 10-Aug-16 6:55am

This is simple logic, just have if on text change and skip whole logic when blank.

Member 12659926 10-Aug-16 6:59am

if I do that textbox will accept all alphabets.

Member 12659926 10-Aug-16 6:59am

I have place the code in textbox1_textchanged() is that right

charmyvora 10-Aug-16 7:04am

Yes... Here is perfect code for you. Will avoid your exception as well

private void textBox1_TextChanged(object sender, EventArgs e)
{
System.Text.RegularExpressions.Regex myRegex = new System.Text.RegularExpressions.Regex("^[a-fA-F0-9]+$");
string text = textBox1.Text;
bool isHex = myRegex.IsMatch(text);
if (!isHex && text.Length > 0)
{
textBox1.Text = text.Substring(0, text.Length - 1);
textBox1.SelectionStart = textBox1.Text.Length;
}
}

Member 12659926 10-Aug-16 7:07am

thanks for reply,now textbox Is accepting a to z,i need upto f only

charmyvora 10-Aug-16 7:08am

z!! I do not think my code do that. please recheck.

charmyvora 10-Aug-16 7:09am

Your reg expression is wrong. Kindly copy paste my code in solution below

Member 12659926 10-Aug-16 6:30am

private void TextBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
if (IsHexadecimal(Strings.Chr(e.KeyValue)) == false && e.KeyCode != Keys.Back) {
e.Handled = true;
e.SuppressKeyPress = true;
}
}
In this Strings.Chr is showing as error.i am using visual studio 2012.

charmyvora 10-Aug-16 7:05am

Do not do on key down. see above comment

W∴ Balboos, GHB 10-Aug-16 6:44am

One modification I would make in the above solution logic: simply always replace the contents of the textbox with the regex-processed string - no need to test if it actually did anything to the original string - much simpler logic and 100% as effective.

charmyvora 10-Aug-16 7:06am

I have posted as a separate solution. Please comment there

Member 12659926 10-Aug-16 7:07am

thanks for reply,now textbox Is accepting a to z,i need upto f only

Member 12659926 10-Aug-16 7:09am

sorry,i made small mistake,its working fine,thank u so much

charmyvora 10-Aug-16 7:10am

Thanks. Please rate my solution when you see it

Solution 2

C#

private void textBox1_TextChanged(object sender, EventArgs e)
        {
            System.Text.RegularExpressions.Regex myRegex = new System.Text.RegularExpressions.Regex("^[a-fA-F0-9]+$");
            string text = textBox1.Text;
            bool isHex = myRegex.IsMatch(text);
            if (!isHex && text.Length > 0)
            {
                textBox1.Text = text.Substring(0, text.Length - 1);
                textBox1.SelectionStart = textBox1.Text.Length;
            }

}

Posted 10-Aug-16 0:56am

charmyvora

Updated 10-Aug-16 1:05am

v2

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BillWoodruff · Accepted Answer · 2016-08-10T04:54:00

There is a much simpler way to do this:

C#

public const string HexLetters = "0123456789abcdefABCDEF\b"; // \b is the BackSpace character

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    if (! HexLetters.Contains(e.KeyChar)) e.Handled = true;
}

The KeyPress EventHandler is fired after the KeyDown Event, and gives us an easy way to get the character of the key that was pressed.

If the current character is not in the set of characters we want to allow, then setting e.Handled = true; in the KeyPress EventHandler will stop the current character from being "passed on" to other possible subscribers.