Bonnie,

Thanks for the inspiration. It was what I needed to get started. I replaced the code in your KeyPressHandler with this:

if  (! CheckKeyPress(e.KeyChar) )
{
	SystemSounds.Beep.Play();
	e.Handled = true;
	return;
}

and added the following method:

protected bool CheckKeyPress(char TheKey)
{
	string LeftText = this.Text.Substring(0, this.SelectionStart);
	string RightText = this.Text.Substring(this.SelectionStart + this.SelectionLength);
	string TestText;

	//----- Check for control keys
	if ( char.IsControl(TheKey) )
	{
		//----- Pass through controls other than ctrl-v (Paste)
		if (TheKey != '\u0016')
			return true;

		//----- Handle Paste ctrl-v (Paste)
		IDataObject ClipData = Clipboard.GetDataObject();
		if ((ClipData == null) || (! ClipData.GetDataPresent(DataFormats.Text)) )
		{
			//-----  Nothing to paste, but something might get deleted
			TestText = LeftText + RightText;
		}
		else
		{
			string InsText = (string)ClipData.GetData(DataFormats.StringFormat);
			
			//-----  Check for illegitimate characters in clipboard text
			foreach ( char ch in InsText.ToCharArray() )
				if ( Array.IndexOf(this.AllowedChars, ch) < 0 )
				return false;
			
			//-----  Check pasted text
			TestText = LeftText + InsText + RightText;
		}
	}
	else
	{
		//-----Discard any undesirable characters
		if (Array.IndexOf(this.AllowedChars, TheKey) < 0)
			return false;
		
		//----- Prevent duplicates of decimal point and minus sign
		if ((TheKey == '.' || TheKey == '-')
				&& (LeftText.IndexOf(TheKey) >= 0 || RightText.IndexOf(TheKey) >= 0))
			return false;

		TestText = LeftText + TheKey + RightText;
	}
	
	if  (this.m_DecimalPlaces == 0)
		return  true;
	
	//----- Check for too many digits on the right side of decimal point
	int I = TestText.IndexOf(".");
	
	if (I < 0)
		I = TestText.Length - 1;
	if  (TestText.Length - I - 1 > this.m_DecimalPlaces)
		return false;
	else
		return true;
}

It checks the number of digits after the decimal. I didn't think it necessary to check the count of digits left of the decimal point, as that should be caught by the maximum value, but it would obviously be easy to add. It passes control keys through so cut, copy, paste, undo and backspace work. And just for grins I added a beep when it discards an entry.

I know some purists don't like more than one return in a method, but I sometimes find the code easier to read with multiple returns.

The only thing that I am aware it doesn't do is validate insertions via Shift-Ins. To do that I have to handle the KeyDown event or override the ProcessCmdKey method and that was a little more complicated than I had time or energy for today.

If you use the code and find any issues, please let me know. I haven't tested it for every combination of settings yet, but my brain needs a rest. I learned a lot today about keyboard input vis-a-vis the .Net framework and about control events, and I grew my C# muscles a bit and explored several blind alleys.

Thanks again,
...Jim