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TEdit: Controlling
userīs input
Date: Sun, 23 May 1999 12:05:13 +1200
(copied and edited from a message posted on borland.public.cppbuilder.language)
Q: I want a TEdit that allows the user
to enter a float value but doesn't let the user enter
anything else.
A: Try this:
void __fastcall TForm1::Edit1Change(TObject
*Sender)
{
static AnsiString lastvalid = "";
if (Edit1->Text == "")
return;
try
{
Edit1->Text.ToDouble();
lastvalid
= Edit1->Text;
}
catch (...)
{
Edit1->Text
= lastvalid;
}
}
When this routine fires it tries to convert (using
AnsiString::ToDouble(), although you could use StrToFloat()
just as well) and if there's an error resets the text
to the last known good value. Empty strings aren't
tested, etc. I tried it out and the worst that
happens is it calls itself again if an invalid number
is entered.
BTW: if you are running this program from the compiler
then it is most likely that you will still see the exceptions
and it will break at the line containing the conversion,
even though you've wrapped it in a try...catch statement.
This is normal behavior for debugging and you can just
continue on as though it was a normal breakpoint.
Or if it really annoys you, you can turn off certain
exceptions in the debugger options. That way it
won't drop back to the debugger every time the exception
is thrown. When not debugging (ie: running the
program normally) you won't see exceptions that are
caught by your program.
Corey Murtagh
The Electric Monk
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