TextBox - TextChanged event Windows C#

Question

I am stuck into a problem and need inputs. Here is the description -

I have a txtPenaltyDays in windows form C#

private void txtPenaltyDays_TextChanged(object sender, EventArgs e)
{
  if(Convert.ToInt16(txtPenaltyDays.Text) > 5)
  {
    MessageBox.Show("The maximum amount in text box cant be more than 5"); 
    txtPenaltyDays.Text = 0;// Re- triggers the TextChanged 
  }
}

But I am running into problem because this fires 2 times. Because of setting the text value to 0. My requirement is that it should fire only one time and set the value to 0.

Any suggestion is deeply appreciated.

a more serious problem. What happen if your user types a letter ? — Steve
– Steve, Commented Oct 9, 2014 at 17:31
Yes steve its true . this is just a part of code i tried to put . But in actual code i have key-press event handling all the special characters — Suzane
– Suzane, Commented Oct 9, 2014 at 17:33

Steve · Accepted Answer · 2014-10-09 17:43:51Z

8

Just disable the event handler when you discover the invalid value, inform the user and then reenable the event handler

 private void txtPenaltyDays_TextChanged(object sender, EventArgs e)
 {
   short num;
   if(Int16.TryParse(txtPenaltyDays.Text, out num))
   {
       if(num > 5)
       {
           txtPenaltyDays.TextChanged -= txtPenaltyDays_TextChanged;
           MessageBox.Show("The maximum amount in text box cant be more than 5"); 
           txtPenaltyDays.Text = "0";//
           txtPenaltyDays.TextChanged += txtPenaltyDays_TextChanged;
       }
   }
   else
   {
      txtPenaltyDays.TextChanged -= txtPenaltyDays_TextChanged;
      MessageBox.Show("Typed an invalid character- Only numbers allowed"); 
      txtPenaltyDays.Text = "0";
      txtPenaltyDays.TextChanged += txtPenaltyDays_TextChanged;
   }
 }

Notice also that I have removed the Convert.ToInt16 because it fails if your user types a letter instead of a number and used Int16.TryParse

edited Oct 9, 2014 at 17:43

answered Oct 9, 2014 at 17:36

Steve

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2 Comments

Suzane Over a year ago

Thanks Steve...that works! Thanks guys for your inputs however i understand that private variable option was not a good one because this will prevent re-trigger on application level.

Steve Over a year ago

Did you consider to use the NumericUpDown control? It has Minimum and Maximum properties that control the allowable values. And it removes the key press handling code. For simple scenarios it is a valuable option

C-Pound Guru · Accepted Answer · 2014-10-09 17:32:38Z

4

You can use a private form field to keep the event from firing the 2nd time:

private bool _IgnoreEvent = false;

private void txtPenaltyDays_TextChanged(object sender, EventArgs e)
 {
   if (_IgnoreEvent) { return;}
   if(Convert.ToInt16(txtPenaltyDays.Text)>5)
    MessageBox.Show("The maximum amount in text box cant be more than 5"); 
    _IgnoreEvent = true;
    txtPenaltyDays.Text = 0;// Re- triggers the TextChanged, but will be ignored 
    _IgnoreEvent = false;
 }

A better question would be, "should I do this in TextChanged, or would it be better to do it in Validating?"

answered Oct 9, 2014 at 17:32

C-Pound Guru

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1 Comment

Steve Coleman Over a year ago

This is the best method. Adding and removing events for something so small is not a good pattern

Masoud · Accepted Answer · 2014-10-09 17:40:16Z

3

Try following code

private void txtPenaltyDays_TextChanged(object sender, EventArgs e)
{
   if(Convert.ToInt16(txtPenaltyDays.Text)>5)
   {
      MessageBox.Show("The maximum amount in text box cant be more than 5"); 
      txtPenaltyDays.TextChanged -= txtPenaltyDays_TextChanged; 
      txtPenaltyDays.Text = 0;// Re- triggers the TextChanged 
      txtPenaltyDays.TextChanged += txtPenaltyDays_TextChanged;
   }
}

answered Oct 9, 2014 at 17:40

Masoud

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Comments

catastrophic error · Accepted Answer · 2014-10-09 17:35:26Z

1

You could use the event Leave or LostFocus instead.

answered Oct 9, 2014 at 17:35

catastrophic error

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Comments

Core · Accepted Answer · 2016-01-17 17:06:00Z

1

You can check if textbox is not focused then fire the event:

if (!textbox1.Focused) return;

or bind and unbind the event:

textbox1.TextChanged -= textbox1_TextChanged; textbox.Text = "some text"; textbox1.TextChanged += textbox1_TextChanged;

answered Jan 17, 2016 at 17:06

Core

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