LCL: Improve Checkbox / TAction synchronization. Issue #39869.

lcl/actnlist.pas

@@ -153,6 +153,7 @@ type
     FCaption: TTranslateString;
     FChecked: Boolean;
     FChecking: Boolean;
+    FGrayed: Boolean;    // The client control (Checkbox) is in 3rd grayed state.
     FDisableIfNoHandler: Boolean;
     FEnabled: Boolean;
     FGroupIndex: Integer;
@@ -195,10 +196,10 @@ type
     function DoHint(var HintStr: string): Boolean; virtual;
     function Execute: Boolean; override;
   public
-    property AutoCheck: Boolean
-                              read FAutoCheck write  SetAutoCheck default False;
+    property AutoCheck: Boolean read FAutoCheck write SetAutoCheck default False;
     property Caption: TTranslateString read FCaption write SetCaption;
     property Checked: Boolean read FChecked write SetChecked default False;
+    property Grayed: Boolean read FGrayed write FGrayed;
     property DisableIfNoHandler: Boolean read FDisableIfNoHandler
                                         write FDisableIfNoHandler default False;
     property Enabled: Boolean read FEnabled write SetEnabled default True;

lcl/include/buttoncontrol.inc

@@ -73,7 +73,8 @@ end;
 function TButtonActionLink.IsCheckedLinked: Boolean;
 begin
   Result:=inherited IsCheckedLinked
-          and (FClientButton.Checked = (Action as TCustomAction).Checked);
+          and ( (FClientButton.Checked = TCustomAction(Action).Checked)
+            or (TCustomAction(Action).Grayed) );
 end;
 
 procedure TButtonActionLink.SetChecked(Value: Boolean);

lcl/include/customaction.inc

@@ -85,7 +85,8 @@ var
   I: Integer;
   Action: TContainedAction;
 begin
-  if FChecking or (Value=FChecked) then exit;
+  if FChecking then exit;
+  if (Value=FChecked) and not FGrayed then exit;
   FChecking := True;
   try
     for I := 0 to FClients.Count - 1 do

lcl/include/customcheckbox.inc

@@ -24,11 +24,50 @@
   Set new state of the checkbox.
  ------------------------------------------------------------------------------}
 procedure TCustomCheckBox.SetState(Value: TCheckBoxState);
+var
+  OldCheckState: TCheckBoxState;
+  OldActionListState: TActionListState;
+  LAction: TBasicAction;
 begin
+  LAction := Action;            // property getter is function, call only once.
+  // TAction does not have the 3rd state, nothing meaningful can be done then
+  if Value <> cbGrayed then begin
+    // no infinite recursion when we would be called again later by TAction itself
+    if not ClicksDisabled then begin
+      if LAction is TCustomAction then begin
+        TCustomAction(LAction).Checked := Value = cbChecked;
+        Exit;
+      end;
+    end;
+  end;
+
   if FState <> Value then
   begin
+    OldCheckState := FState;
     FState := Value;
+
     ApplyChanges;
+
+    // some widgetsets like gtk* do not allow to uncheck a radio button
+    // only call OnChange if effectivelly changed
+    FState := RetrieveState;
+    if FState <> OldCheckState then begin
+      if LAction is TCustomAction then begin
+        // Prevent triggering a linked Action when State = cbGrayed.
+        if FState = cbGrayed then begin
+          OldActionListState := TCustomAction(LAction).ActionList.State;
+          TCustomAction(LAction).ActionList.State := asSuspended;
+          TCustomAction(LAction).Grayed := True;
+        end;
+      end;
+      DoClickOnChange;
+      if LAction is TCustomAction then begin
+        if FState = cbGrayed then
+          TCustomAction(LAction).ActionList.State := OldActionListState
+        else
+          TCustomAction(LAction).Grayed := False;
+      end;
+    end;
   end;
 end;
 
@@ -141,26 +180,11 @@ end;
   Set the new state of the checkbox as boolean.
  ------------------------------------------------------------------------------}
 procedure TCustomCheckBox.SetChecked(Value : Boolean);
-var
-  OldState: TCheckBoxState;
 begin
-  OldState := FState;
   if Value then
-    FState := cbChecked
+    State := cbChecked
   else
-    FState := cbUnChecked;
-  //debugln('TCustomCheckBox.SetChecked ',dbgsname(Self),' ',dbgs(ord(FState)));
-  if FState <> OldState then
-  begin
-    if Action is TCustomAction then
-      TCustomAction(Action).Checked := FState = cbChecked;
-    ApplyChanges;
-    //some widgetsets (gtk*) does not allow to uncheck a radio button
-    //only call OnChange if effectivelly changed
-    FState := RetrieveState;
-    if FState <> OldState then
-      DoClickOnChange;
-  end;
+    State := cbUnChecked;
 end;
 
 procedure TCustomCheckBox.RealSetText(const Value: TCaption);