Validating textbox content if checkbox has been checked

Question

I'm trying to do a validation wherein if a checkbox has been ticked, the corresponding textbox would no longer be in ReadOnly mode and should not be empty. For example, if I checked CheckBox1, if TextBox1 did not have any input, a MessageBox would pop up to say that "Please fill up the entire form!". Else, it would display "Done!".

This is what I have so far:

if ((CheckBox1.Checked && TextBox1.Text == "") 
    || (CheckBox2.Checked && TextBox2.Text == ""))
    MessageBox.Show("Please fill up the entire form!");

else if (CheckBox1.Checked && TextBox1.Text != "")
    MessageBox.Show("Done!");

else if (CheckBox2.Checked && TextBox2.Text != "")
    MessageBox.Show("Done!");

I've made a couple of checkboxes/textboxes that would require this validation and I find that it gets kind of lengthy so I was wondering if there's a simpler/better approach.

(not sure if relevant) Note: I got the toggling the ReadOnly mode when the CheckChanged event is triggered part down

Are you aware that `CheckBox1.Checked == true` is exaxtly the same as `CheckBox1.Checked`? — oerkelens, Oct 15 '17 at 14:02
@oerkelens silly me thanks for that! I always thought i had to do that — nik, Oct 15 '17 at 14:03
@RezaAghaei well at least I think I do. Do you think I don't and can suggest a better way to go around it? — nik, Oct 15 '17 at 14:05
You can return from method if there is some validation error and don't write those `else if` part. Just put the code which should be executed after validations. — Reza Aghaei, Oct 15 '17 at 14:06

Reza Aghaei · Accepted Answer · 2017-10-15T14:32:36.387

There could be some enhancements for your code, for example:

You can use this criteria !textBox.ReadOnly && string.IsNullOrEmpty(textBox.Text) rather than what you have.
You can avoid using those else if parts and just return from the method if there is a validation error and just put the code after the validation block.

A better solution - Using Validating Event

But I'd rather to change the whole style of validation and use Validating event of those TextBox controls. To do so, you need to follow these instructions:

1) Set AutoValidate property of form to EnableAllowFocusChange in design mode or using code in Load event of form.

2) Handle Validating event of all TextBox controls using single a method and set e.Cancel = true; when there is validation error:

private void textBox_Validating(object sender, CancelEventArgs e)
{
    var textBox = (TextBox)sender;
    if (!textBox.ReadOnly && string.IsNullOrEmpty(textBox.Text))
        e.Cancel = true;
}

3) In the save button of your form, using ValidateChildren method of the form, check if there is any validation error, show a message, otherwise do what the button is supposed to do:

private void button1_Click(object sender, EventArgs e)
{
    if (!this.ValidateChildren())
        MessageBox.Show("Please correct validation errors.")
    else
        MessageBox.Show("Done!")
}

Note

To read more about validation options in Windows Forms, take a look at this post:

Validating user input / Give .NET controls status OK or NOK

Also if you want to enhance the user experience by showing a validation error/icon near the control using an ErrorProvider, take a look at this post:

Validation using Validating event and ErrorProvider - Show Error Summary

Oh so this is what you meant. Thank you so much for that elaborate explanation. Worked like a charm! :) — nik, Oct 16 '17 at 03:25
I recommend you to take a look at linked posts as well. Maybe it seems too much for a simple application, but knowing facilities is a key point which will help you when creating more complicated and more professional applications. — Reza Aghaei, Oct 16 '17 at 03:36
I got around to just now. The detailed explanations are really helpful. Thank you! — nik, Oct 16 '17 at 13:53

Validating textbox content if checkbox has been checked

1 Answers1