Synchronize scrolling for two components
lazarus / 62-General

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wcage03 · 2018-11-07 23:44

I am trying to have multiple TDBGrid components on a page and have
them all scroll horizontally in sync (i.e. if the horizontal scroll
bar is moved left or right on any one of the components, all will move
accordingly).  I have searched for a couple of days on this and I can
find the topic in numerous places for other components (mainly TMemo),
but I unable to get the examples to work.

Conceptually, I need to be notified that a component is scrolling;
capture the scroll position and push that out to the others.  I am not
making progress.  I have one example that I found that I have focused
on, without luck.  Again, it is for a TMemo, but I figure once I get a
solution I can fit it into another component (or at least know that it
won't work, if that is the case).  I have attached the code that I
found in my search that seemed most straightforward.  When I compile,
I get an error in the overridden create method where the handler is
being replaced.

If anyone could point me in the right direction with this sample code
or toward something more appropriate i would appreciate it.

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils, Forms,
Controls, Graphics, Dialogs, StdCtrls, msghandler,  LCLType, LCLIntf,
Buttons, Messages; type   TMemo=class(StdCtrls.TMemo) // Just to add
things to TMemo class only for this unit  private   
 BusyUpdating:Boolean; // To avoid circular stack overflow   
 SyncMemo:TMemo; // To remember the TMemo to be sync   
 Old_WindowProc:TWndMethod; // To remember old handler     procedure
New_WindowProc(var Mensaje:TMessage); // The new handler  public   
 constructor Create(AOwner:TComponent);override; // The new
constructor     destructor Destroy;override; // The new destructor 
end;   { TForm1 }   TForm1 = class(TForm)    Memo1: TMemo;    Memo2:
TMemo;    procedure FormCreate(Sender: TObject);  private    procedure
pnlMemo2Resize(Sender: TObject);  public   end; var  Form1:
TForm1; implementation {$R *.lfm}procedure TMemo.New_WindowProc(var
Mensaje:TMessage);begin     Old_WindowProc(Mensaje); // Call the real
handle before doing anything     if  (WM_PAINT<>Mensaje.Msg) // If not
when need to be repainted to improve speed       or       
 BusyUpdating // To avoid circular stack overflow       or       
 (not Assigned(SyncMemo)) // If not yet set (see TForm1.FormCreate
bwlow)     then Exit; // Do no more and exit the procedure   
 BusyUpdating:=True; // Set that object is busy in our special action 
   SyncMemo.Perform(WM_HSCROLL,SB_THUMBPOSITION+65536*GetScrollPos(Han
dle,SB_HORZ),0); // Send to the other TMemo a message to set its
horizontal scroll as it is on this TMemo     BusyUpdating:=False; //
Set that the object is no more busy in our special
actionend; constructor TMemo.Create(AOwner:TComponent); // The new
constructorbegin     inherited Create(AOwner); // Call real
constructor     BusyUpdating:=False; // Initialize as not being in
use, to let enter     Old_WindowProc:=WindowProc; // Remember old
handler     WindowProc:=New_WindowProc; // Replace handler with new
oneend; destructor TMemo.Destroy; // The new destructorbegin   
 WindowProc:=Old_WindowProc; // Restore the original handler   
 inherited Destroy; // Call the real destructorend; procedure
TForm1.FormCreate(Sender: TObject);begin     Memo1.SyncMemo:=Memo2; //
Tell Memo1 what TMemo must sync (Memo2)     Memo2.SyncMemo:=Memo1; //
Tell Memo2 what TMemo must sync (Memo1)end; procedure
TForm1.pnlMemo2Resize(Sender: TObject);begin   
 //Memo2.Height:=pnlMemo2.Height+20; // Make height enough big to
cause horizontal scroll bar be out of TPanel visible area, so it will
not be seen by the userend; end.