iOS: Pick up theme palette from system colors

For now we just fill out the system palette, and react to the system
changing theme from dark to light. A further improvement would be to
fill in the control-specific palettes.

Change-Id: I764db4415f5b55ccb193dae43e9f4386c765b30b
Fixes: QTBUG-42944
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/plugins/platforms/ios/qiosscreen.mm b/src/plugins/platforms/ios/qiosscreen.mm
index 9aba658479..c3376c08e8 100644
--- a/src/plugins/platforms/ios/qiosscreen.mm
+++ b/src/plugins/platforms/ios/qiosscreen.mm
@@ -45,6 +45,7 @@
 #include "qiosapplicationdelegate.h"
 #include "qiosviewcontroller.h"
 #include "quiview.h"
+#include "qiostheme.h"
 
 #include <QtCore/private/qcore_mac_p.h>
 
@@ -207,6 +208,18 @@ static QIOSScreen* qtPlatformScreenFor(UIScreen *uiScreen)
     [super sendEvent:event];
 }
 
+- (void)traitCollectionDidChange:(UITraitCollection *)previousTraitCollection
+{
+    [super traitCollectionDidChange:previousTraitCollection];
+
+    if (self.screen == UIScreen.mainScreen) {
+        if (previousTraitCollection.userInterfaceStyle != self.traitCollection.userInterfaceStyle) {
+            QIOSTheme::initializeSystemPalette();
+            QWindowSystemInterface::handleThemeChange<QWindowSystemInterface::SynchronousDelivery>(nullptr);
+        }
+    }
+}
+
 @end
 
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