c# winform key press delete add 0

Question

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.

 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");



        }

Answer 1

@Booney , I agree with the solution of vb2ae, you could try to use textbox.keyup event to get what you want.

I make a sample code and you could have a look.

Code:

 private void Form1_Load(object sender, EventArgs e)  
        {  
            textBox1.Text = "0";  
        }  
        private void textBox1_KeyUp(object sender, KeyEventArgs e)  
        {  
            if (e.KeyCode == Keys.Back&&textBox1.Text=="")  
            {  
                textBox1.Text = "0";  
            }  
            if(!int.TryParse(textBox1.Text, out int i))  
            {  
                MessageBox.Show("Please enter number and don't contain other character");  
                textBox1.Text=textBox1.Text.Remove(textBox1.Text.Length - 1,1);  
            }  
        }  
   

Result:

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Answer 2

You should think about moving the code into the keyup or keypress event for the textbox. This will give you the keypressed so you can blank the textbox text if delete or backspace is pressed and value is 0

https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.control.keyup?view=net-5.0