From 9f577dc5482422641419f105590452731717f2e3 Mon Sep 17 00:00:00 2001
From: Juha <juha@lazarus-ide.org>
Date: Sun, 18 Sep 2022 21:17:56 +0300
Subject: [PATCH] LCL: Add an option to NOT call TCheckbox OnChange handler
 when clicked. Issue #39870, patch by Arioch The.

---
 lcl/include/buttoncontrol.inc  |  3 ++-
 lcl/include/customcheckbox.inc | 23 ++++++++++++++---------
 lcl/stdctrls.pp                |  5 +++++
 3 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/lcl/include/buttoncontrol.inc b/lcl/include/buttoncontrol.inc
index e6e3984e34..9c2adf2436 100644
--- a/lcl/include/buttoncontrol.inc
+++ b/lcl/include/buttoncontrol.inc
@@ -51,7 +51,8 @@ end;
 
 procedure TButtonControl.Click;
 begin
-  DoOnChange;
+  if not FSkipOnChangeOnClick then
+    DoOnChange;
   inherited Click;
 end;
 
diff --git a/lcl/include/customcheckbox.inc b/lcl/include/customcheckbox.inc
index 9bad674b64..8daac80965 100644
--- a/lcl/include/customcheckbox.inc
+++ b/lcl/include/customcheckbox.inc
@@ -115,7 +115,13 @@ end;
 
 procedure TCustomCheckBox.Click;
 begin
-  // skip clicks by WM_MOUSEUP
+  if VCL_OnClick_Emulation then Exit;
+  FSkipOnChangeOnClick := True;
+  try
+    inherited Click;
+  finally
+    FSkipOnChangeOnClick := False;
+  end;
 end;
 
 function TCustomCheckBox.RetrieveState: TCheckBoxState;
@@ -130,13 +136,12 @@ begin
   end;
 end;
 
-{------------------------------------------------------------------------------
-  Method: TCustomCheckBox.Create
-  Params:  TheOwner: the owner of the class
-  Returns: Nothing
+class constructor TCustomCheckBox.CreateClass;
+begin
+  VCL_OnClick_Emulation := True;
+  inherited;
+end;
 
-  Constructor for custom checkbox.
- ------------------------------------------------------------------------------}
 constructor TCustomCheckBox.Create(TheOwner: TComponent);
 begin
   inherited Create(TheOwner);
@@ -276,8 +281,8 @@ end;
 procedure TCustomCheckBox.DoClickOnChange;
 begin
   Changed;
-  // emulate delphi OnClick behaviour (click will call OnChange)
-  if not ClicksDisabled then
+  // emulate delphi OnClick behaviour (inherited .Click will call DoOnChange)
+  if VCL_OnClick_Emulation and not ClicksDisabled then
     inherited Click
   else
     DoOnChange;
diff --git a/lcl/stdctrls.pp b/lcl/stdctrls.pp
index 63d3816ced..9c6a5da745 100644
--- a/lcl/stdctrls.pp
+++ b/lcl/stdctrls.pp
@@ -1181,6 +1181,8 @@ type
     function IsCheckedStored: boolean;
     procedure WMDefaultClicked(var Message: TLMessage); message LM_CLICKED;
   protected
+    // Do not call OnChange when clicked, required by TCustomCheckBox
+    FSkipOnChangeOnClick: boolean;
     class procedure WSRegisterClass; override;
     function GetActionLinkClass: TControlActionLinkClass; override;
     function GetChecked: Boolean; virtual;
@@ -1353,6 +1355,9 @@ type
     procedure TextChanged; override;
     procedure CreateParams(var Params: TCreateParams); override;
   public
+    // VCL calls OnChange when clicked. This can be turned off for a more logical behavior.
+    class var VCL_OnClick_Emulation: boolean;
+    class constructor CreateClass;
     constructor Create(TheOwner: TComponent); override;
   public
     property Alignment: TLeftRight read GetAlignment write SetAlignment default taRightJustify;