Add trait to get layout anchors for a view, implement it on common co…

…mponents and add some functions that make use of it to simplify creating layout constraints

src/layout/has_layout_impl.rs

@@ -0,0 +1,116 @@
+use super::traits::HasLayout;
+use crate::{
+    button::Button,
+    input::TextField,
+    layout::{LayoutAnchorX, LayoutAnchorY, LayoutConstraint, SafeAreaLayoutGuide},
+    listview::ListView,
+    text::Label,
+    view::View,
+};
+
+/// Takes a list of views, a parent view that  contains them and returns layout constraints that will position them from top to bottom separated by the specified padding.
+/// The padding is also applied to the sides of each view.
+pub fn top_to_bottom(views: Vec<&dyn HasLayout>, parent: &impl HasLayout, padding: f32) -> Vec<LayoutConstraint> {
+    let (top, bottom) = if let (Some(first), Some(last)) = (views.first(), views.last()) {
+        (
+            first.get_top().constraint_equal_to(parent.get_top()).offset(padding),
+            last.get_bottom().constraint_equal_to(parent.get_bottom()).offset(padding),
+        )
+    } else {
+        // No views were passed
+        return Vec::new();
+    };
+    let adjoining_constraints = views
+        .windows(2)
+        .map(|views| views[0].get_bottom().constraint_equal_to(views[1].get_top()));
+    let side_constraints = views
+        .iter()
+        .map(|view| [view.get_leading().constraint_equal_to(parent.get_leading()).offset(padding)])
+        .flatten();
+    vec![top, bottom]
+        .into_iter()
+        .chain(adjoining_constraints)
+        .chain(side_constraints)
+        .collect()
+}
+
+/// Returns a list of layout constraints that makes the given view fill the given safe area
+pub fn fill_safe_area(view: &impl HasLayout, safe_area: &SafeAreaLayoutGuide) -> Vec<LayoutConstraint> {
+    vec![
+        view.get_top().constraint_equal_to(&safe_area.top),
+        view.get_bottom().constraint_equal_to(&safe_area.bottom),
+        view.get_leading().constraint_equal_to(&safe_area.leading),
+        view.get_trailing().constraint_equal_to(&safe_area.trailing),
+    ]
+}
+
+impl HasLayout for Label {
+    fn get_top(&self) -> &LayoutAnchorY {
+        &self.top
+    }
+    fn get_bottom(&self) -> &LayoutAnchorY {
+        &self.bottom
+    }
+    fn get_leading(&self) -> &LayoutAnchorX {
+        &self.leading
+    }
+    fn get_trailing(&self) -> &LayoutAnchorX {
+        &self.trailing
+    }
+}
+impl HasLayout for TextField {
+    fn get_top(&self) -> &LayoutAnchorY {
+        &self.top
+    }
+    fn get_bottom(&self) -> &LayoutAnchorY {
+        &self.bottom
+    }
+    fn get_leading(&self) -> &LayoutAnchorX {
+        &self.leading
+    }
+    fn get_trailing(&self) -> &LayoutAnchorX {
+        &self.trailing
+    }
+}
+impl HasLayout for Button {
+    fn get_top(&self) -> &LayoutAnchorY {
+        &self.top
+    }
+    fn get_bottom(&self) -> &LayoutAnchorY {
+        &self.bottom
+    }
+    fn get_leading(&self) -> &LayoutAnchorX {
+        &self.leading
+    }
+    fn get_trailing(&self) -> &LayoutAnchorX {
+        &self.trailing
+    }
+}
+impl<T> HasLayout for View<T> {
+    fn get_top(&self) -> &LayoutAnchorY {
+        &self.top
+    }
+    fn get_bottom(&self) -> &LayoutAnchorY {
+        &self.bottom
+    }
+    fn get_leading(&self) -> &LayoutAnchorX {
+        &self.leading
+    }
+    fn get_trailing(&self) -> &LayoutAnchorX {
+        &self.trailing
+    }
+}
+impl<T> HasLayout for ListView<T> {
+    fn get_top(&self) -> &LayoutAnchorY {
+        &self.top
+    }
+    fn get_bottom(&self) -> &LayoutAnchorY {
+        &self.bottom
+    }
+    fn get_leading(&self) -> &LayoutAnchorX {
+        &self.leading
+    }
+    fn get_trailing(&self) -> &LayoutAnchorX {
+        &self.trailing
+    }
+}

src/layout/mod.rs

@@ -47,3 +47,5 @@ mod safe_guide;
 
 #[cfg(feature = "autolayout")]
 pub use safe_guide::SafeAreaLayoutGuide;
+#[cfg(feature = "autolayout")]
+mod has_layout_impl;

src/layout/traits.rs

@@ -15,6 +15,8 @@ use crate::objc_access::ObjcAccess;
 #[cfg(feature = "appkit")]
 use crate::pasteboard::PasteboardType;
 
+use super::{LayoutAnchorX, LayoutAnchorY};
+
 /// A trait that view wrappers must conform to. Enables managing the subview tree.
 #[allow(unused_variables)]
 pub trait Layout: ObjcAccess {
@@ -173,3 +175,11 @@ pub trait Layout: ObjcAccess {
         });
     }
 }
+
+/// A trait to access a views layout anchors
+pub trait HasLayout {
+    fn get_top(&self) -> &LayoutAnchorY;
+    fn get_bottom(&self) -> &LayoutAnchorY;
+    fn get_leading(&self) -> &LayoutAnchorX;
+    fn get_trailing(&self) -> &LayoutAnchorX;
+}