Prevent continue Typing in TextBox When a Char is Entered

Question

I have a textbox which user should type a price in it. I need to prevent continue typing if price starts with 0. For example user can not type "000" or "00009".

I tried this on KeyPress, but nothing!

if (txt.Text.StartsWith("0"))
       return; Or e.Handeled = true;

Refusing to allow any typing when the price starts with 0 seems like a poor user experience - notably, they may want to type a backspace to *remove* the character if they entered it in error. A softer approach that highlights the text box and refuses to submit the entire form, whilst allowing edits/corrections would usually be preferred. — Damien_The_Unbeliever, Nov 07 '16 at 07:54
Yes User can backspace and delete, but if it starts with 0 it can not type another char. — Inside Man, Nov 07 '16 at 07:55
Should it be `e.Handeled = true`? [Reference](http://stackoverflow.com/a/2591284/1050927), and you may need to check user input `numeric` instead of control character (backspace, delete...) — Prisoner, Nov 07 '16 at 08:05

score 2 · Accepted Answer · answered Nov 07 '16 at 08:13

try this:

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    //only allow digit and (.) and backspace
    if ((e.KeyChar < '0' || e.KeyChar > '9') && e.KeyChar != '\b' && e.KeyChar != '.')
    {
        e.Handled = true;
    }

    var txt = sender as TextBox;

    //only allow one dot
    if (txt.Text.Contains('.') && e.KeyChar == (int)'.')
    {
        e.Handled = true;
    }

    //if 0, only allow 0.xxxx
    if (txt.Text.StartsWith("0")
        && !txt.Text.StartsWith("0.")
        && e.KeyChar != '\b'
        && e.KeyChar != (int)'.')
    {
        e.Handled = true;
    }
}

instead of `e.KeyChar != '\b'` it is better to use `!char.IsControl(e.KeyChar)` — Inside Man, Nov 07 '16 at 13:20

score 0 · Answer 2 · answered Nov 07 '16 at 07:57

0

You could use the TextChanged-event for this.

private void textBox1_TextChanged(object sender, EventArgs e)
{
    if (this.textBox1.Text == "0") this.textBox1.Text = "";
}

This will only work, if the TextBox is empty on startup.

answered Nov 07 '16 at 07:57

Wudge

357
1
6
14

I do not want to empty the text box after entering 0 at start. I just want to prevent continue typing in this situation. – Inside Man Nov 07 '16 at 08:00
You can still use text changed – Henrik Bøgelund Lavstsen Nov 07 '16 at 08:02

score 0 · Answer 3 · answered Nov 07 '16 at 08:07

0

I solved it Myself:

private void txtPrice_KeyPress(object sender, KeyPressEventArgs e)
{
    if (txtPrice.Text.StartsWith("0") && !char.IsControl(e.KeyChar))
    {
        e.Handled = true;
        return;
    }
}

answered Nov 07 '16 at 08:07

Inside Man

4,194
12
59
119

Prevent continue Typing in TextBox When a Char is Entered

3 Answers3