Qt: Emit scrolled callback when dragging scrollbar

This is supposed to be emitted whenever the user performs an
intentional interaction, which works whenever you scroll the Slint
Flickable with the scrollwheel. Dragging the scrollbar on the Qt
style didn't do anything, since that was never hooked up to this
callback.

I only implemented this in the Qt style, because that's the only
one that uses the NativeScrollView element.

See #9574.

Author: redstrate

internal/backends/qt/qt_widgets/scrollview.rs

@@ -25,6 +25,7 @@ pub struct NativeScrollView {
     pub has_focus: Property<bool>,
     pub vertical_scrollbar_policy: Property<ScrollBarPolicy>,
     pub horizontal_scrollbar_policy: Property<ScrollBarPolicy>,
+    pub scrolled: Callback<VoidArg>,
     data: Property<NativeSliderData>,
     widget_ptr: std::cell::Cell<SlintTypeErasedWidgetPtr>,
     animation_tracker: Property<i32>,
@@ -198,7 +199,12 @@ impl Item for NativeScrollView {
                                 return -value;
                         }
                     });
-                    value_prop.set(LogicalLength::new(-(new_val.min(max).max(0) as f32)));
+                    let old_val = value_prop.get();
+                    let new_val = LogicalLength::new(-(new_val.min(max).max(0) as f32));
+                    value_prop.set(new_val);
+                    if new_val != old_val {
+                        Self::FIELD_OFFSETS.scrolled.apply_pin(self).call(&());
+                    }
                     InputEventResult::EventIgnored
                 }
                 MouseEvent::Moved { .. } => {
@@ -207,21 +213,30 @@ impl Item for NativeScrollView {
                         let new_val = data.pressed_val
                             + ((pos as f32) - data.pressed_x) * (max + (page_size as f32))
                                 / size as f32;
-                        value_prop.set(LogicalLength::new(-new_val.min(max).max(0.)));
+                        let old_val = value_prop.get();
+                        let new_val = LogicalLength::new(-new_val.min(max).max(0.));
+                        value_prop.set(new_val);
+                        if new_val != old_val {
+                            Self::FIELD_OFFSETS.scrolled.apply_pin(self).call(&());
+                        }
                         InputEventResult::GrabMouse
                     } else {
                         InputEventResult::EventAccepted
                     }
                 }
                 MouseEvent::Wheel { delta_x, delta_y, .. } => {
+                    let max = max as f32;
+                    let new_val;
                     if horizontal {
-                        let max = max as f32;
-                        let new_val = value as f32 + delta_x;
-                        value_prop.set(LogicalLength::new(new_val.min(0.).max(-max)));
+                        new_val = value as f32 + delta_x;
                     } else {
-                        let max = max as f32;
-                        let new_val = value as f32 + delta_y;
-                        value_prop.set(LogicalLength::new(new_val.min(0.).max(-max)));
+                        new_val = value as f32 + delta_y;
+                    }
+                    let old_val = value_prop.get();
+                    let new_val = LogicalLength::new(new_val.min(0.).max(-max));
+                    value_prop.set(new_val);
+                    if new_val != old_val {
+                        Self::FIELD_OFFSETS.scrolled.apply_pin(self).call(&());
                     }
                     InputEventResult::EventAccepted
                 }

internal/compiler/builtins.slint

@@ -658,6 +658,7 @@ export component NativeScrollView {
     in property <ScrollBarPolicy> vertical-scrollbar-policy;
     in property <ScrollBarPolicy> horizontal-scrollbar-policy;
     in property <bool> enabled: true;
+    callback scrolled;
     //-default_size_binding:expands_to_parent_geometry
     //-is_internal
 }

internal/compiler/widgets/qt/internal-scrollview.slint

@@ -39,6 +39,8 @@ export component InternalScrollView {
 
         horizontal-max: fli.viewport-width > fli.width ? fli.viewport-width - fli.width : 0phx;
         horizontal-page-size: fli.width;
+
+        scrolled => root.scrolled();
     }
 
     fli := Flickable {