QStyleSheetStyle: add new property to QPushButton: icon

There is currently no proper way to change the icon of a
pushbutton from css. But there is a need for doing so
(QTBUG-2982), and the typical work-around is to instead use
the css property 'qproperty-icon'. But setting qproperties
from the style is not a good idea in the first place, since
it modifies the state of the widget it draws. Moreover, such
properties are only set once (in QStyle::polish()), and
will not have any effect on pseudo states, like hover.

To close this gap, this patch will add a css property
'icon' that can be set on a QPushButton. This property
will follow normal css cascading, and respect pseudo
states, equal to any other css property.

[ChangeLog][QtWidgets][QStyle] You can now set the
CSS property 'icon' on a QPushButton to override
which icon to draw.

Fixes: QTBUG-79137
Change-Id: Ie7e0b0fa4f19471f51108cd4ca931356219d562e
Reviewed-by: Christian Ehrlicher <ch.ehrlicher@gmx.de>
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

1 files changed, 17 insertions, 0 deletions

diff --git a/src/widgets/doc/src/widgets-and-layouts/stylesheet.qdoc b/src/widgets/doc/src/widgets-and-layouts/stylesheet.qdoc
index c8f374a1b1..35bad6786a 100644
--- a/src/widgets/doc/src/widgets-and-layouts/stylesheet.qdoc
+++ b/src/widgets/doc/src/widgets-and-layouts/stylesheet.qdoc
@@ -993,6 +993,9 @@
         \li Supports the \l{box model}. Supports the \l{#default-ps}{:default},
            \l{#flat-ps}{:flat}, \l{#checked-ps}{:checked} pseudo states.
 
+           Since 5.15, the \l{#icon-prop}{icon} property can be set to
+           override the button icon.
+
            For QPushButton with a menu, the menu indicator is styled
            using the \l{#menu-indicator-sub}{::menu-indicator}
            subcontrol. Appearance of checkable push buttons can be
@@ -1946,6 +1949,20 @@
            See also \l{#width-prop}{width}.
 
     \row
+        \li \b{\c icon} \target icon-prop
+        \li \l{#Url}{Url}+
+        \li The icon that is used, for widgets that have an icon.
+
+        The only widget currently supporting this property is QPushButton.
+
+        \note It's the application's responsibilty to assign an icon to a
+        button (using the QAbstractButton API), and not the style's. So be
+        careful setting it unless your stylesheet is targeting a specific
+        application.
+
+        Available since 5.15.
+
+    \row
         \li \b{\c icon-size} \target icon-size-prop
         \li \l{#Length}{Length}
         \li The width and height of the icon in a widget.