Add method to stack/list to add class by idx (#378)

src/views/list.rs

@@ -1,7 +1,7 @@
 use super::{v_stack_from_iter, Decorators, Stack};
 use crate::context::StyleCx;
 use crate::reactive::create_effect;
-use crate::style::Style;
+use crate::style::{Style, StyleClassRef};
 use crate::view::View;
 use crate::EventPropagation;
 use crate::{
@@ -50,6 +50,10 @@ impl List {
         self.onaccept = Some(Box::new(on_accept));
         self
     }
+    pub fn add_class_by_idx(mut self, class: impl Fn(usize) -> StyleClassRef) -> Self {
+        self.child = self.child.add_class_by_idx(class);
+        self
+    }
 }
 
 /// A list of views built from an iterator which remains static and always contains the same elements in the same order.

src/views/stack.rs

@@ -3,7 +3,7 @@ use taffy::style::FlexDirection;
 use crate::{
     context::UpdateCx,
     id::Id,
-    style::Style,
+    style::{Style, StyleClassRef},
     view::{View, ViewData, Widget},
     view_tuple::ViewTuple,
 };
@@ -173,3 +173,13 @@ impl Widget for Stack {
         }
     }
 }
+
+impl Stack {
+    pub fn add_class_by_idx(self, class: impl Fn(usize) -> StyleClassRef) -> Self {
+        for (index, child) in self.children.iter().enumerate() {
+            let style_class = class(index);
+            child.view_data().id().add_class(style_class);
+        }
+        self
+    }
+}