C＃-限制文本框中的某些字符

Question

I am trying to limit the amount of a certain character (in my case a comma (,)) inside my textbox. I want it to only allow max 9 commas in the textbox. If the user attempts to add more commas than 9, it should display a messagebox with the error, and then also not allow the user to enter more into the textbox.

In my application, I allow the user to add 10 tags to a textbox separated by commas.

An example input by the user could look like this: summer,sexy,hot,beautiful,girls,guys,food,music,funny,lol

That is the max limit of tags allowed in the textbox (9 commas). And when they reach that limit, it should block them from typing any more commas. I hope I was clear enough.

Here is my code so far. My textbox is called tagBox.

private void tagBox_TextChanged(object sender, EventArgs e)
        {
            // Allow max 10 tags in the tag box
            string tags = tagBox.Text;
            int count = tags.Split(',').Length - 1;
            if (count > 9)
            {
                MessageBox.Show("Max 10 tags are allowed.", "Notice", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
            }
        }

I only managed to make the messagebox appear. But how do I stop them from typing in more commas?

Answer 1

It should look something like this:

private void tagBox_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)
{
    // Allow max 10 tags in the tag box
    string tags = tagBox.Text;
    int count = tags.Split(',').Length - 1;
    if (count > 9 && e.KeyChar == ',')
    {
        e.Handled = true;
        MessageBox.Show("Max 10 tags are allowed.", "Notice", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
    }
    else        
        e.Handled = false;
}

Answer 2

I think you should do something like this

    Public class TagTextBox : TextBox
    {
        Public override OnKeyDown(object sender, KeyEventArgs args)
        {
            // Do logic here
            // Call this to accept Key
            base.OnKeyDown(sender, args);
         }
    }