Merge #583

583: Add default mounted() method to Component trait r=jstarry a=hgzimmerman

Fixes #572

I made the choice to have `on_mount()` not return a `ShouldRender` bool, because I don't think there is a situation where altering parts of a component state relevant to the `view()` should ever take place in `on_mount()` instead of `create()`. Let me know your thoughts, because its an easy enough change to make.

Co-authored-by: Henry Zimmerman <zimhen7@gmail.com>

src/html/mod.rs

@@ -24,6 +24,10 @@ pub trait Component: Sized + 'static {
     type Properties: Properties;
     /// Initialization routine which could use a context.
     fn create(props: Self::Properties, link: ComponentLink<Self>) -> Self;
+    /// Called after the component has been attached to the VDOM and it is safe to receive messages
+    /// from agents but before the browser updates the screen. If true is returned, the view will
+    /// be re-rendered and the user will not see the initial render.
+    fn mounted(&mut self) -> ShouldRender { false }
     /// Called everytime when a messages of `Msg` type received. It also takes a
     /// reference to a context.
     fn update(&mut self, msg: Self::Message) -> ShouldRender;

src/html/scope.rs

@@ -112,20 +112,24 @@ struct CreatedState<COMP: Component> {
 }
 
 impl<COMP: Component + Renderable<COMP>> CreatedState<COMP> {
+    /// Called once immediately after the component is created.
+    fn mounted(mut self) -> Self {
+        if self.component.mounted() {
+            self.update()
+        } else {
+            self
+        }
+    }
+
     fn update(mut self) -> Self {
         let mut next_frame = self.component.view();
         let node = next_frame.apply(&self.element, None, self.last_frame, &self.env);
         if let Some(ref mut cell) = self.occupied {
             *cell.borrow_mut() = node;
         }
 
-        Self {
-            env: self.env,
-            component: self.component,
-            last_frame: Some(next_frame),
-            element: self.element,
-            occupied: self.occupied,
-        }
+        self.last_frame = Some(next_frame);
+        self
     }
 }
 
@@ -178,7 +182,9 @@ where
     fn run(self: Box<Self>) {
         let current_state = self.shared_state.replace(ComponentState::Processing);
         self.shared_state.replace(match current_state {
-            ComponentState::Ready(state) => ComponentState::Created(state.create().update()),
+            ComponentState::Ready(state) => {
+                ComponentState::Created(state.create().update().mounted())
+            },
             ComponentState::Created(_) | ComponentState::Destroyed => current_state,
             ComponentState::Empty | ComponentState::Processing => {
                 panic!("unexpected component state: {}", current_state);