Validating WinForms TextBox (in C#)

Question

In TextBox_Leave event i need to check whether numbers entered in textbox is in serial number or not.If it is not in order then i need to display a message as "number" is missing

For example :

In textbox i have entered 3 and click tab : I need to display message as "Number is not in order , number "1" and "2" is missing "

Answer 1

I don't know whether this also works in c#2.0, this is my experience in c#3.0:

Why do you use TextBox_Leave for that? The Validating-event should be used for validating whether input is correct.

Combine using the Validating-event with using an ErrorProvider (you can just drag it from the toolbox onto the form) to set an error message: it will be displayed as a (blinking) exclamation mark in a red triangle.

An ErrorProvider can also block any submit-actions.

Answer 2

Alternatively you can also use Validating event of the text box.

  private void textBox1_Validating( object sender, CancelEventArgs e )
  {
      if ( textBox1.Text == "3" )
          e.Cancel = true;
  }

The text-box wont loose focus until it receives a valid input.

Answer 3

Try using a Masked TextBox control and set a custom property for this type of field validation.

Answer 4

I will show you how to validate Validating WinForms TextBox (in C#).

1. Create a function:

   public static void ChkBlankTextBoxes(object sender, string type)
   {
   
       if (sender is TextBox)
       {
           TextBox textbox = sender as TextBox;
           if (string.IsNullOrEmpty(textbox.Text))
           {
               MessageBox.Show("Please enter correct value value..");
               textbox.Focus();
   
           }
       }
   }
   

2. Call to created function:

   ChkBlankTextBoxes(txt_userID, textBoxtype);
   
   ChkBlankTextBoxes(txt_password, textBoxtype);
   

Answer 5

One trick is to retain focus in the textbox when trying to leave (with TAB for instance) in case of some condition (missing number):

 private void textBox1_Leave(object sender, EventArgs e)
    {
        TextBox tb = (TextBox)sender;

        if (tb.Text == "3")
            tb.Focus();
    }

Assuming you are using a standard textbox. You could also use third party controls that where you can cancel an event (e.Cancel = true) on some condition.