Setting palettes for specific widgets/widget classes?

[Zoë]

What is the correct way to make a QPalette apply to all controls of a specific type? 

Using raw QT objects, I can use QApplication_setPalette(Palette, 'QCheckBox') or QWidget_setPalette(Widget, Palette);  Neither of those work for me for LCL backed controls, and modifying the TQtWidget(Handle).Palette.Handle doesn't seem to have an effect either.  I'm fine with creating any subclasses that would be required.

My specific goal is an application-wide dark mode palette, but at least with the Fusion style, checkboxes use QPaletteWindow for the square indicator frame, so they're almost invisible if the window itself is dark too.  I'd want to override just QPaletteWindow for QCheckBox, QListItem, and ideally TQtThemeServices.DrawElement(tbCheckBox*).

Since TQtThemeServices.DrawElement needs the palette applied using QStyleOption_setPalette, I don't see a way to do that with the existing ThemeServices API.  I could extract the relevant bits though.  Alternatively, would it make sense to query the palette from the context's parent at the top where it's initializing QPainter_setBackground?

For the LCL controls, the project I'm currently testing with is:

1) Create a new LCLQt5 project.
2) Add a TCheckbox and a TListView that has a single item and has Checkboxes := True.
3) Add an OnShow handler that creates a second form using the raw Qt API with matching controls, and sets the application/widget palettes appropriately:

Code: Pascal  [Select][+][-]

1. procedure TForm1.FormShow(Sender: TObject);
2. type
3.   TQPaletteColorRole = QPaletteWindowText..QPaletteToolTipText;
4. const
5.   AppPalette: array[TQPaletteColorRole] of TColorRef = (
6.     $eeeeee, $353535, $4b4b4b, $404040, $232323, $2c2c2c, $eeeeee, $0000ff,
7.     $eeeeee, $282828, $353535, $2d2d2d, $a75824, $ffffff, $ff5500, $ff5500,
8.     $353535, $000000, $2d2d2d, $eeeeee);
9. var
10.   Check: QCheckBoxH;
11.   S: WideString;
12. var
13.   Palette: QPaletteH;
14.   QColor: TQColor;
15.   ColorRole: TQPaletteColorRole;
16.   List: QListWidgetH;
17.   Item: QListWidgetItemH;
18.   RawWindow: QMainWindowH;
19. begin
20.   S := 'Raw QT';
21.   // Create raw window
22.   RawWindow := QMainWindow_Create;
23.   QWidget_resize(RawWindow, Scale96ToScreen(220), Scale96ToScreen(150));
24.   // Raw checkbox
25.   Check := QCheckBox_Create(@S, RawWindow);
26.   QWidget_setGeometry(Check, Scale96ToScreen(10), Scale96ToScreen(10),
27.     Scale96ToScreen(200), Scale96ToScreen(20));
28.   QWidget_show(Check);
29.   // Raw listbox with checkboxes
30.   List := QListWidget_Create(RawWindow);
31.   QWidget_setGeometry(List, Scale96ToScreen(10), Scale96ToScreen(40),
32.     Scale96ToScreen(200), Scale96ToScreen(100));
33.   Item := QListWidgetItem_Create(@S, List);
34.   QListWidgetItem_setFlags(Item, QListWidgetItem_flags(Item) or QtItemIsUserCheckable);
35.   QListWidgetItem_setCheckState(Item, QtUnchecked);
36.   Item := QListWidgetItem_Create(@S, List);
37.   QListWidgetItem_setFlags(Item, QListWidgetItem_flags(Item) or QtItemIsUserCheckable);
38.   QListWidgetItem_setCheckState(Item, QtChecked);
39.   QWidget_show(List);
40.   // Show raw window
41.   QWidget_show(RawWindow);
42.   // Set default application palette
43.   Palette := QPalette_Create();
44.   try
45.     QColor := Default(TQColor);
46.     for ColorRole := Low(ColorRole) to High(ColorRole) do
47.     begin
48.       ColorRefToTQColor(AppPalette[ColorRole], QColor);
49.       QPalette_setColor(Palette, ColorRole, @QColor);
50.     end;
51.     QApplication_setPalette(palette);
52.   finally
53.     QPalette_Destroy(Palette);
54.   end;
55.   // Set control-specific palettes
56.   Palette := QPalette_Create();
57.   try
58.     ColorRefToTQColor(clLime, QColor);
59.     QPalette_setColor(Palette, QPaletteWindow, @QColor);
60.     // Update for all QCheckBoxes and QListViews
61.     QApplication_setPalette(Palette, 'QCheckBox');
62.     QApplication_setPalette(Palette, 'QListView');
63.     // Try to set for LCL checkbox?
64.     QWidget_setPalette(TQtWidget(CheckBox1.Handle).Widget, Palette); // Doesn't work
65.     QPalette_setColor(TQtWidget(CheckBox1.Handle).Palette.Handle, // Doesn't work
66.       QPaletteWindow, @QColor);
67.   finally
68.     QPalette_Destroy(Palette);
69.   end;
70. end;
71.  

With that code the raw QCheckBox and QListWidget have bright green borders, but the TCheckbox and TListView are both still dark-on-dark.

I'd prefer to avoid using stylesheets if possible, since that requires fully specifying the appearance of all of the checkbox states.  Overriding just QCheckbox::indicator's border color isn't enough.

[zeljko]

Palette can be setted up at application level (Fusion style), but control by control never worked for me,
I'm afraid that your problem can be fixed only via stylesheets.