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Technical Information Database TI1171D.txt Validating input in TEdit components Category :VCL Platform :All Product :Delphi All Description: Q: How can I validate input in my TEdit components? A: Assuming you're using regular TEdit components, during OnExit, you will see irregular behavior from controls if you attempt to change focus at that time. The solution is to post a message to your form in the TEdit's OnExit event handler. This user-defined posted message will indicate that the coast is clear to begin validating input. Since posted messages are placed at the end of the message queue, this gives Windows the opportunity to complete the focus change before you attempt to change the focus back to another control. Attached is a unit and text representation of a DFM (form) file which demonstrates this technique. { *** BEGIN CODE FOR UNIT5.PAS *** } unit Unit5; interface uses SysUtils, WinTypes, WinProcs, Messages, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls, Mask; const { User-defined message } um_ValidateInput = wm_User + 100; type TForm5 = class(TForm) Edit1: TEdit; Edit2: TEdit; Edit3: TEdit; Edit4: TEdit; Button1: TButton; procedure EditExit(Sender: TObject); procedure EditEnter(Sender: TObject); private Refocusing: TObject; { User-defined message handler } procedure ValidateInput(var M: TMessage); message um_ValidateInput; end; var Form5: TForm5; implementation {$R *.DFM} procedure TForm5.ValidateInput(var M: TMessage); var E : TEdit; begin { The following line is my validation. I want to make sure } { the first character is a lower case alpha character. Note } { the typecast of lParam to a TEdit. } E := TEdit(M.lParam); if not (E.Text[1] in ['a'..'z']) then begin Refocusing := E; { Avoid a loop } ShowMessage('Bad input'); { Yell at the user } TEdit(E).SetFocus; { Set focus back } end; end; procedure TForm5.EditExit(Sender: TObject); begin { Post a message to myself which indicates it's time to } { validate the input. Pass the TEdit instance (Self) as } { the message lParam. } if Refocusing = nil then PostMessage(Handle, um_ValidateInput, 0, longint(Sender)); end; procedure TForm5.EditEnter(Sender: TObject); begin if Refocusing = Sender then Refocusing := nil; end; end. { *** END CODE FOR UNIT5.PAS *** } { *** BEGIN CODE FOR UNIT5.DFM *** } object Form5: TForm5 Left = 489 Top = 303 Width = 318 Height = 205 Caption = 'Form5' Font.Color = clWindowText Font.Height = -13 Font.Name = 'System' Font.Style = [] PixelsPerInch = 96 TextHeight = 16 object Edit1: TEdit Left = 32 Top = 32 Width = 121 Height = 24 TabOrder = 0 Text = 'Edit1' OnEnter = EditEnter OnExit = EditExit end object Edit2: TEdit Left = 160 Top = 32 Width = 121 Height = 24 TabOrder = 1 Text = 'Edit2' OnEnter = EditEnter OnExit = EditExit end object Edit3: TEdit Left = 32 Top = 64 Width = 121 Height = 24 TabOrder = 2 Text = 'Edit3' OnEnter = EditEnter OnExit = EditExit end object Edit4: TEdit Left = 160 Top = 64 Width = 121 Height = 24 TabOrder = 3 Text = 'Edit4' OnEnter = EditEnter OnExit = EditExit end object Button1: TButton Left = 112 Top = 136 Width = 89 Height = 33 Caption = 'Button1' TabOrder = 4 end end { *** END CODE FOR UNIT5.DFM *** } Reference: 7/16/98 4:34:03 PM
Article originally contributed by Borland Staff
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