Merge pull request #122 from hecrj/feature/event-subscriptions

Event subscriptions

src/application.rs

@@ -1,4 +1,4 @@
-use crate::{Command, Element, Settings};
+use crate::{Command, Element, Settings, Subscription};
 
 /// An interactive cross-platform application.
 ///
@@ -117,6 +117,20 @@ pub trait Application: Sized {
     /// [`Command`]: struct.Command.html
     fn update(&mut self, message: Self::Message) -> Command<Self::Message>;
 
+    /// Returns the event [`Subscription`] for the current state of the
+    /// application.
+    ///
+    /// A [`Subscription`] will be kept alive as long as you keep returning it,
+    /// and the __messages__ produced will be handled by
+    /// [`update`](#tymethod.update).
+    ///
+    /// By default, this method returns an empty [`Subscription`].
+    ///
+    /// [`Subscription`]: struct.Subscription.html
+    fn subscription(&self) -> Subscription<Self::Message> {
+        Subscription::none()
+    }
+
     /// Returns the widgets to display in the [`Application`].
     ///
     /// These widgets can produce __messages__ based on user interaction.
@@ -168,6 +182,10 @@ where
         self.0.update(message)
     }
 
+    fn subscription(&self) -> Subscription<Self::Message> {
+        self.0.subscription()
+    }
+
     fn view(&mut self) -> Element<'_, Self::Message> {
         self.0.view()
     }

src/native.rs

@@ -1,6 +1,6 @@
 pub use iced_winit::{
     Align, Background, Color, Command, Font, HorizontalAlignment, Length,
-    VerticalAlignment,
+    Subscription, VerticalAlignment,
 };
 
 pub mod widget {

src/sandbox.rs

@@ -1,4 +1,4 @@
-use crate::{Application, Command, Element, Settings};
+use crate::{Application, Command, Element, Settings, Subscription};
 
 /// A sandboxed [`Application`].
 ///
@@ -149,6 +149,10 @@ where
         Command::none()
     }
 
+    fn subscription(&self) -> Subscription<T::Message> {
+        Subscription::none()
+    }
+
     fn view(&mut self) -> Element<'_, T::Message> {
         T::view(self)
     }