How can I only accept numbers from an edit control?

Question

Normally I would like to do the following to store a string value in a database

DataModule.tbTableNumber.Value := StrToFloat(edtNumber.text); 

Now the problem occurs when the user enters something that cannot be converted to a number. How can I prevent this? Can a person use an exception and how can I write this exception?

I am using Delphi XE2.

Answer 1

The best solution (IMHO) is to use TryStrToFloat :

 procedure TForm1.Button1Click(Sender: TObject); var myfloat: double; begin if TryStrToFloat(Edit1.Text, myfloat) then DataModule.tbTableNumber.Value := myfloat else ShowMessage('Incorrect value.'); end; 

I don’t think that the use of try..except is especially “clean” when the error is as trivial and, in fact, as expected, as in this case.

Answer 2

You can catch the exception with the following

  try val := StrToFloat(edtNumber.text); except on E: EConvertError do begin ShowMessage( 'Entered Data is not a valid Floating Point number' ); end; end; 

You can also watch

 StrToFloatDef( edtNumber.text, -1 ) 

If you just need to make sure that you convert returns a real number

Answer 3

There are many controls that can only be allowed to accept numerical input, and this has some advantages over the one you took as your answer.

The jedi JVCL library , for example, includes several numeric input controls, and the main VCL includes several features, including the Spin Edit control, which is designed to enter integer values.

Answer 4

I found a solution at http://www.festra.com/eng/snip05.htm

(code from the link)

 procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char); begin if not (Key in [#8, '0'..'9', '-', DecimalSeparator]) then begin ShowMessage('Invalid key: ' + Key); Key := #0; end else if ((Key = DecimalSeparator) or (Key = '-')) and (Pos(Key, Edit1.Text) > 0) then begin ShowMessage('Invalid Key: twice ' + Key); Key := #0; end else if (Key = '-') and (Edit1.SelStart <> 0) then begin ShowMessage('Only allowed at beginning of number: ' + Key); Key := #0; end; end;