Textbox don't allow typing " \ " 2 times after each other

Question

I bumped into a problem, i hope someone can help me out :) i got a textbox, and i want to limit users so that it isn't allowed to have two \ after each other. i'm using it for folders. for example: C\temp\test\ now i want to make it not possible to type C\temp\test\\

i've tried searching some around for this problem but i couldn't find anyting like this. so i hope it's possible :)

heres a code of my textbox how it is now

    private void textBox1_TextChanged(object sender, EventArgs e)
    {
        try
        {
            Regex regex = new Regex(@"[^C^D^A^E^H^S^T^]");
            MatchCollection matches = regex.Matches(textBox1.Text);
            if (matches.Count > 0)
            {
                MessageBox.Show("Character niet toegestaan!");
                textBox1.Text = "";
            }

            clsOpslagMedium objOpslag;  // definieert type object 
            objOpslag = new clsOpslagMedium();  // creert opject in memory
            objOpslag.DriveLetterString = textBox1.Text;
        }
        catch (Exception variableEx1)
        {
            MessageBox.Show("Foutmelding: " + variableEx1.Message);
        }
    }

I hope someone can give some examples and that I provided enough information :)

why don't you just use `textBox1.Text.Contains(@"\\")` to test if you got 2 \\next each other ? — Rémi, Jun 19 '13 at 14:25
Sorry pierre, i bumped into a problem and posted it tiwce, i didn't mean to do this — Ricje20, Jun 19 '13 at 14:42
This is a bad idea. First, paths are allowed to contain two backslashes, eg `\\myserver\myshare\mydirectory\myfile.txt`. Second, if you want users to browse folders, **create a folder browser control**, not a text box. Third, you're going to have to write code that handles malformed paths regardless; there are lots more ways to malform a path than just two backslashes, so don't bother restricting the input. Allow all the input and then give a good error message if its bad. Fifth, catching all exceptions is a bad programming practice; catch only the exceptions you intend to handle. — Eric Lippert, Jun 19 '13 at 14:51
Sixth, eliminating double backslashes as people type leads to bad situations. For example, suppose I type `c:\d\e.txt` and then I realize whoops, I meant to write `c:\f\e.txt`, so I put the cursor after the `d`, hit backspace, the double-backslash disappears and now I end up with either `c:\fe.txt` or `c:f\e.txt`, neither of which is what I want. You're trying to be too clever here, and producing a user experience that is frustrating and unpredictable. — Eric Lippert, Jun 19 '13 at 14:54
@EricLippert I think he just poorly worded what he wanted in the original question, he left a comment in keyboardP's answer which makes me think he really just wants to use a `ErrorProvider` and a check on the control's `Validating` event (and I added a answer explaining how to do do). — Scott Chamberlain, Jun 19 '13 at 14:59
It would make things a Ton easier if i could post a screenshot >.< but i don't have enough reputation — Ricje20, Jun 25 '13 at 07:07

keyboardP · Answer 1 · 2013-06-19T14:36:00.293

3

An easy way would be to simply replace the string.

private void textBox1_TextChanged(object sender, EventArgs e)
{
    //get the current cursor position so we can reset it 
    int start = textBox1.SelectionStart;

    textBox1.Text = Regex.Replace(textBox1.Text, @"\\\\+", @"\");

    //make sure the cursor does reset to the beginning
    textBox1.Select(start, 0);
}

The extra code surrounding the replace ensures the cursor doesn't reset to the start of the textbox (which happens when you set the Text property).

edited Jun 19 '13 at 14:36

answered Jun 19 '13 at 14:24

keyboardP

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Would this work if someone pasted "c:\temp\\\" ? – EkoostikMartin Jun 19 '13 at 14:30
Yes, it will replace any number of sequential backslashes with one instance. – keyboardP Jun 19 '13 at 14:32
he could test in in a loop `while (textBox1.Text.Contains(@"\\")){textBox1.Text = Regex.Replace(textBox1.Text, @"\\+", @"\");}` – Rémi Jun 19 '13 at 14:32
Oh, you edited your answer to @"\\+" :) – EkoostikMartin Jun 19 '13 at 14:33
@EkoostikMartin - Just in time :D – keyboardP Jun 19 '13 at 14:36
a textreplace isn't working in my case. i need an error shown up when a user leaves the box when he types more then one \ – Ricje20 Jun 19 '13 at 14:36
1

@Ricje20 - you said "don't allow typing" and "make it not possible to type". So now you are changing the requirements... – EkoostikMartin Jun 19 '13 at 14:38
@Ricje20 Then you'll want `if (Regex.IsMatch(textBox1.Text, @"\\{2,}")) // error` – Nolonar Jun 19 '13 at 14:38
@Ricje20 - Your question stated you wanted to prevent them from typing in two slashes. Nolonar's solution will work if you just want to perform a check. – keyboardP Jun 19 '13 at 14:38
1

I think your patten is matching unnecessary matches, `@"\\\\+"` would be better. You need doubled up because the regex engine needs them escaped too, just like you would need to if you did not include `@` (if you did not include `@` your pattern would need to be `\\\\\\\\+`) – Scott Chamberlain Jun 19 '13 at 14:39
@ScottChamberlain - Thanks for the optimization tip, I've updated the answer. – keyboardP Jun 19 '13 at 14:40

Frank59 · Answer 2 · 2013-06-19T14:50:08.593

0

You need to find all \-sequences (\\,\\\,\\\\, ...) and replace that on \. You can use regex for search sequences

Sample:

      string test=@"c:\\\adas\\dasda\\\\\\\ergreg\\gwege";
       Regex regex = new Regex(@"\\*");


       MatchCollection matches = regex.Matches(test);
        foreach (Match match in matches)
        {
            if (match.Value!=string.Empty)
                test = ReplaceFirst(test, match.Value, @"\");
        }

edited Jun 19 '13 at 14:50

answered Jun 19 '13 at 14:27

Frank59

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can you give a little example? ~thanks for the answer! – Ricje20 Jun 19 '13 at 14:28

score 0 · Accepted Answer · edited May 23 '17 at 10:25

a textreplace isn't working in my case. i need an error shown up when a user leaves the box when he types more then one \

If this is what you really want you need to use a ErrorProvider. Add one to your form then add the following code to the texbox's Validating event and be sure that CausesValidation is true for the textbox

private void textBox1_Validating(object sender, CancelEventArgs e)
{
    if(Regex.IsMatch(textBox1.Text, @"\\\\+"))
    {
        e.Cancel = true;
        errorProvider1.SetError(textbox1, @"\\ Is not allowed");
    }
    else
    {
        errorProvider1.SetError(textbox1, null);
    }
}

This will make a ! show up next to the text box if they type wrong and force them to correct it when they attempt to leave the text box.

Textbox don't allow typing " \ " 2 times after each other

3 Answers3

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