C# winform key press delete add 0

Question

0.00/5 (No votes)

See more:

Doing a bit of math if a user enters a number in a textbox and press delete or backspace textbox will show (0) zero instead of blank.
Any help appreciated.

What I have tried:

C#

<pre>private void OnTextChanged(object sender, EventArgs e)
         {
                     
             if (int.TryParse(txt_BackedOut.Text, out int i) && int.TryParse(txt_TOTAL.Text, out int j) && int.TryParse(txt_Online.Text, out int t))
                 txt_Different.Text = (j - i - t).ToString();   
    
             if (txt_Online.Text == "")
                 MessageBox.Show("Please enter Zero or another number in the textbox");    
              
         }

Posted 2-Oct-21 14:15pm

Member 12349103

Updated 3-Oct-21 23:38pm

Add a Solution

3 solutions

Solution 1

This is really easy if you use the debugger to follow what the code is doing.

This:

C#

txt_Different.Text = (j - i - t).ToString();

is where the 0 is coming from. If none of the text in the textboxes can be parsed, the values of those variables is going to be 0. The you're essentially calling 0.ToString(), which is going to return the string "0".

Posted 2-Oct-21 14:32pm

Dave Kreskowiak

Solution 3

You can use the KeyDown event, for example:

private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
    if (e.KeyCode == Keys.Delete || e.KeyCode == Keys.Back)
    {
        e.Handled = true;
        textBox1.Text = "0";
    }
}

You are strongly recommended to use NumericUpDown in stead of TextBox.

Posted 3-Oct-21 23:38pm

adriancs

Updated 3-Oct-21 23:40pm

v3

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

BillWoodruff · Accepted Answer · 2021-10-02T23:10:00

1) modifying the standard behavior of key entry in a Control violates user interface guidelines: it will probably confuse users. 'delete clears the current selection; why deprive the user of that functunality ?

2) You have 4 TextBoxes, assuming 'OnTextChanged is the TextChanged event handler for all 4:

a) if 'txt_Different is used only to display the result of calculations, why allow the user to type in it. consider using a Label.

b) if any of the attempts to parse 'txt_BackedOut, 'txt_TOTAL, 'txt_Online fail, why test 'txt_Different, and possibly change it?

Here's something to help you get started:

private TextBox currentTextBox;

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    currentTextBox = sender as TextBox;

    char key = e.KeyChar;

    bool allowkey =
        (Char.IsNumber(key) || key == '\b')
        &&
        (currentTextBox.Text.Length >  0 && key != '0');

    e.Handled = ! allowkey;
}

This event handler checks each character entered: if the character is a number, or a backspace; then the entry of '0' is prevented if it's the first character. Note that delete is not disabled, and that cut, and paste, are not disabled.

i have strong opinions about how data-entry should be handled/validated in cases like this; i'll be happy to share them, but, first, i'd like to see you consider what i've said here and revise your code.