C# edit for number and uppercase letters

13y5.2kVisual Basic .NET

In a C# 2010 desktop application, I want a textbox field to contain only letters in upper case. In addition, I want to allow for numbers. Any other values are not valid for this textbox field.

Thus can you show me code on how to setup the edit for uppercase letters and numbers only in the textbox?

10 Replies

Know the answer? Post it — somebody with the same question will find it here.

Iftikar Hussain13y ago
Hi,
You can use Leave event of the textbox to check your input. It work for both copy paste and normal typing.

this.textBox1.Leave += new System.EventHandler(this.textBox1_TextLeave);

private void textBox1_TextLeave(object sender, EventArgs e)
{
var text = textBox1.Text.Trim();
if (Regex.IsMatch(text, @"^[A-Z0-9]+$"))
{
// Do something here
}
else
{
MessageBox.Show("Doesn't match pattern");
}
}

Regards,
Iftikar
0
Vulpes13y ago
Unless you use a custom textbox, preventing the user from pasting invalid characters into a textbox isn't easy and many developers just give it up and disable pasting altogether or allow the user to paste anything in and then validate it when focus leaves the textbox.

If you use a custom text box (i.e. one which derives from the standard textbox), then all you have to do is to trap the WM_PASTE message, examine the clipbpoard contents and reject them if they're invalid. However, you then have to remember to use the custom textbox when you need the functionality in question.

The KeyChar property returns a char i.e. the unicode character corresponding to the key or combination of keys pressed. As the most commonly used characters are those in the ASCII range you can get their codes from examining an ASCII table:

http://www.asciitable.com/

Alternatively, you can use a char literal instead of its code:

if ((e.KeyChar >= '0' && e.KeyChar <= '9') || (e.KeyChar >= 'A' && e.KeyChar <= 'Z') || e.KeyChar == '\b') return;
0
dc13y ago
The code youy have listed below,Try handling the TextBox's KeyPress event as follows:

        private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
        {
            if ((e.KeyChar >= 48 && e.KeyChar <= 57) || (e.KeyChar >= 65 && e.KeyChar <= 90) || e.KeyChar == 8) return;
            e.Handled = true;
        }

Can you tell me where I can look to see what the various values of e.KeyCar means?
0
dc13y ago
Why would I want to prevent a user from copying and pasting results into the testbox? if they copy and paste, the answer would be more correct.
0
Iftikar Hussain13y ago
what is not working? you need to validate onclick of the button. please tell what pattern is valid and invalid.

Regards,
Iftikar
0
Vulpes13y ago
No, handling the KeyPress event won't prevent the user from copying and pasting invalid characters into the TextBox.

However, the easiest way to deal with this is to disable pasting altogether either from the context menu (by right clicking the TextBox) or from the keyboard by pressing either Control-V or Shift-Insert.

This can be done as follows:

public Form1()
{
InitializeComponent();
textBox1.ContextMenu = new ContextMenu(); // effectively disables context menu
}

private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
if ((e.Control && e.KeyCode == Keys.V) || (e.Shift && e.KeyCode == Keys.Insert))
{
e.SuppressKeyPress = true;
}
}

Regarding Iftikar's approach (i.e. post entry validation), the regular expression is not quite right. It should be:

if (Regex.IsMatch(text, @"^[A-Z0-9]+$"))

If you want to allow the TextBox to be left blank, replace + with *
0
dc13y ago
Will keypress work if the user copies and pastes the value into the textbook field
0
dc13y ago
The following code is not working: if (Regex.IsMatch(text, @"^[A-Z](\d)+$"))

How would yu change the code?
0
Iftikar Hussain13y ago
Hi,
You can do this by using Regular Expression

private void button1_Click(object sender, EventArgs e)
{
var text = textBox1.Text.Trim();
if (Regex.IsMatch(text, @"^[A-Z](\d)+$"))
{
// Do something here
}
else
{
MessageBox.Show("Doesn't match pattern");
}
}

Valid - A123, ABC1, ABC111, ABC3783782, AOEIS292999
Invalid - abc, 123, abc123, Abc123

Regards,
Iftikar
0
Vulpes13y ago
Try handling the TextBox's KeyPress event as follows:

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
if ((e.KeyChar >= 48 && e.KeyChar <= 57) || (e.KeyChar >= 65 && e.KeyChar <= 90) || e.KeyChar == 8) return;
e.Handled = true;
}
0