Add default impl for AppDelegate

Also box the AppDelegate inside the function to make it cleaner to call.

Author: LiHRaM

druid/examples/multiwin.rs

@@ -34,9 +34,8 @@ struct State {
 fn main() {
     simple_logger::init().unwrap();
     let main_window = WindowDesc::new(ui_builder).menu(make_menu(&State::default()));
-    let delegate = Box::new(MultiwinDelegate {});
     AppLauncher::with_window(main_window)
-        .delegate(delegate)
+        .delegate(Delegate)
         .launch(State::default())
         .expect("launch failed");
 }
@@ -82,9 +81,9 @@ fn ui_builder() -> impl Widget<State> {
     col
 }
 
-struct MultiwinDelegate {}
+struct Delegate;
 
-impl AppDelegate<State> for MultiwinDelegate {
+impl AppDelegate<State> for Delegate {
     fn event(
         &mut self,
         event: Event,

druid/src/app.rs

@@ -70,8 +70,8 @@ impl<T: Data + 'static> AppLauncher<T> {
     /// Set the [`AppDelegate`].
     ///
     /// [`AppDelegate`]: struct.AppDelegate.html
-    pub fn delegate(mut self, delegate: Box<dyn AppDelegate<T>>) -> Self {
-        self.delegate = Some(delegate);
+    pub fn delegate(mut self, delegate: impl AppDelegate<T> + 'static) -> Self {
+        self.delegate = Some(Box::new(delegate));
         self
     }
 

druid/src/app_delegate.rs

@@ -68,5 +68,10 @@ pub trait AppDelegate<T: Data> {
         data: &mut T,
         env: &Env,
         ctx: &mut DelegateCtx,
-    ) -> Option<Event>;
+    ) -> Option<Event> {
+        let _ = data;
+        let _ = env;
+        let _ = ctx;
+        Some(event)
+    }
 }