Delete (backspace) behavior in MaskedTextBox

Jon Chance

Hi

I have a MaskedTextBox with the following mask 00:00:00:00 and promtChar -. '00:00:00:00' is also the default value I assign to it when the box is entered. It is to enter Timecode into.

I also validate each number as it is entered (on keyDown) to ensure it is valid for its position within the mask. If the number is invalid I suppress the keypress so nothing is entered. This is all working fine.

My issue is what happens when deleting characters. If you delete (using backspace) the second character for example on 11:10:10:24 you are left with 11:01:02:4-, ever thing has shifted down one from the point you deleted. What I want is to end up with 10:10:10:24 or 1-:10:10:24

I would like the promptChar or a 0 to be entered in place of the character deleted. I assume i can't use my promptChar due to the mask I am using only allowing numbers.

To change the behavior of the backspace I have tried to capture the backspace key, convert the maskedTextBox text to a char array and modify this by inserting a '0' into the array to replace the deleted character. By doing this I am padding the array back out (this is working correctly).

I then try to assign this array back to the maskedTextBox. This however is failing and I end up with --:--:--:-- which is my mask.

Any idea why this is not working, is there an easy way to achieve this?

Here is my code:-

if (e.KeyCode == Keys.Back)
{
char[] textAsArray = maskedTextBox1.Text.ToCharArray();
textAsArray[index] = Convert.ToChar("0");
string str = textAsArray.ToString();
maskedTextBox1.Text = str;
}

3 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes14y ago
Sorry, what I had in mind here was not to allow deletions at all (apart from the last character entered) - just overwrites.

Deleting the last character entered would, of course, not be a problem as the previous characters would not be shifted down.
Jon Chance14y ago
Thanks for getting back Vulpes.

Reading up on that property msdn says:

" IsOverwriteMode takes into account both the value of the InsertKeyMode property and the state of the user's keyboard. If InsertKeyMode is set to either Insert or Overwrite, IsOverwriteMode will return false or true, respectively. If InsertKeyMode is set to Default, it will return the state of the INSERT key."

The proprty itself seems to be read only and in my application I already have InsertKeyMode set to Overwrite, so I guess it is set to true.

This does result in text being overwritten when entering new text into the maskedTextBox. It doesn't though seem to have any effect on what happens when deleting a character from the textbox. Characters will still shift down within the maskedtextbox when one is deleted, whereas I'm after replacing the deleted character with a replacement of my chioce (a zero or the promtChar).
Vulpes14y ago
An alternative strategy would be to set the MaskedTextBox's IsOverwriteMode property to true. The user would then only be able to overwrite existing characters, not delete them.