Implement focus_next operation

... as well as a `count_focusable` composable helper!

examples/todos/src/main.rs

@@ -1,12 +1,15 @@
 use iced::alignment::{self, Alignment};
+use iced::event::{self, Event};
+use iced::keyboard;
+use iced::subscription;
 use iced::theme::{self, Theme};
 use iced::widget::{
-    button, checkbox, column, container, row, scrollable, text, text_input,
-    Text,
+    self, button, checkbox, column, container, row, scrollable, text,
+    text_input, Text,
 };
 use iced::window;
 use iced::{Application, Element};
-use iced::{Color, Command, Font, Length, Settings};
+use iced::{Color, Command, Font, Length, Settings, Subscription};
 
 use lazy_static::lazy_static;
 use serde::{Deserialize, Serialize};
@@ -48,6 +51,7 @@ enum Message {
     CreateTask,
     FilterChanged(Filter),
     TaskMessage(usize, TaskMessage),
+    TabPressed,
 }
 
 impl Application for Todos {
@@ -94,11 +98,12 @@ impl Application for Todos {
             }
             Todos::Loaded(state) => {
                 let mut saved = false;
-                let mut task_command = Command::none();
 
-                match message {
+                let command = match message {
                     Message::InputChanged(value) => {
                         state.input_value = value;
+
+                        Command::none()
                     }
                     Message::CreateTask => {
                         if !state.input_value.is_empty() {
@@ -107,29 +112,44 @@ impl Application for Todos {
                                 .push(Task::new(state.input_value.clone()));
                             state.input_value.clear();
                         }
+
+                        Command::none()
                     }
                     Message::FilterChanged(filter) => {
                         state.filter = filter;
+
+                        Command::none()
                     }
                     Message::TaskMessage(i, TaskMessage::Delete) => {
                         state.tasks.remove(i);
+
+                        Command::none()
                     }
                     Message::TaskMessage(i, task_message) => {
                         if let Some(task) = state.tasks.get_mut(i) {
-                            if matches!(task_message, TaskMessage::Edit) {
-                                task_command =
-                                    text_input::focus(Task::text_input_id(i));
-                            }
+                            let should_focus =
+                                matches!(task_message, TaskMessage::Edit);
 
                             task.update(task_message);
+
+                            if should_focus {
+                                text_input::focus(Task::text_input_id(i))
+                            } else {
+                                Command::none()
+                            }
+                        } else {
+                            Command::none()
                         }
                     }
                     Message::Saved(_) => {
                         state.saving = false;
                         saved = true;
+
+                        Command::none()
                     }
-                    _ => {}
-                }
+                    Message::TabPressed => widget::focus_next(),
+                    _ => Command::none(),
+                };
 
                 if !saved {
                     state.dirty = true;
@@ -152,7 +172,7 @@ impl Application for Todos {
                     Command::none()
                 };
 
-                Command::batch(vec![task_command, save])
+                Command::batch(vec![command, save])
             }
         }
     }
@@ -225,6 +245,19 @@ impl Application for Todos {
             }
         }
     }
+
+    fn subscription(&self) -> Subscription<Message> {
+        subscription::events_with(|event, status| match (event, status) {
+            (
+                Event::Keyboard(keyboard::Event::KeyPressed {
+                    key_code: keyboard::KeyCode::Tab,
+                    ..
+                }),
+                event::Status::Ignored,
+            ) => Some(Message::TabPressed),
+            _ => None,
+        })
+    }
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]

native/src/widget/operation.rs

@@ -58,3 +58,96 @@ pub fn focus<T>(target: Id) -> impl Operation<T> {
 
     Focus { target }
 }
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+pub struct FocusCount {
+    focused: Option<usize>,
+    total: usize,
+}
+
+pub fn count_focusable<T, O>(f: fn(FocusCount) -> O) -> impl Operation<T>
+where
+    O: Operation<T> + 'static,
+{
+    struct CountFocusable<O> {
+        count: FocusCount,
+        next: fn(FocusCount) -> O,
+    }
+
+    impl<T, O> Operation<T> for CountFocusable<O>
+    where
+        O: Operation<T> + 'static,
+    {
+        fn focusable(
+            &mut self,
+            state: &mut dyn state::Focusable,
+            _id: Option<&Id>,
+        ) {
+            if state.is_focused() {
+                self.count.focused = Some(self.count.total);
+            }
+
+            self.count.total += 1;
+        }
+
+        fn container(
+            &mut self,
+            _id: Option<&Id>,
+            operate_on_children: &mut dyn FnMut(&mut dyn Operation<T>),
+        ) {
+            operate_on_children(self)
+        }
+
+        fn finish(&self) -> Outcome<T> {
+            Outcome::Chain(Box::new((self.next)(self.count)))
+        }
+    }
+
+    CountFocusable {
+        count: FocusCount::default(),
+        next: f,
+    }
+}
+
+pub fn focus_next<T>() -> impl Operation<T> {
+    struct FocusNext {
+        count: FocusCount,
+        current: usize,
+    }
+
+    impl<T> Operation<T> for FocusNext {
+        fn focusable(
+            &mut self,
+            state: &mut dyn state::Focusable,
+            _id: Option<&Id>,
+        ) {
+            if self.count.total == 0 {
+                return;
+            }
+
+            match self.count.focused {
+                None if self.current == 0 => state.focus(),
+                Some(focused) if focused == self.current => state.unfocus(),
+                Some(focused) if focused + 1 == self.current => state.focus(),
+                Some(focused)
+                    if focused == self.count.total - 1 && self.current == 0 =>
+                {
+                    state.focus()
+                }
+                _ => {}
+            }
+
+            self.current += 1;
+        }
+
+        fn container(
+            &mut self,
+            _id: Option<&Id>,
+            operate_on_children: &mut dyn FnMut(&mut dyn Operation<T>),
+        ) {
+            operate_on_children(self)
+        }
+    }
+
+    count_focusable(|count| FocusNext { count, current: 0 })
+}

src/lib.rs

@@ -192,22 +192,26 @@ use iced_wgpu as renderer;
 use iced_glow as renderer;
 
 pub use iced_native::theme;
+pub use runtime::event;
+pub use runtime::subscription;
 
 pub use application::Application;
 pub use element::Element;
 pub use error::Error;
+pub use event::Event;
 pub use executor::Executor;
 pub use renderer::Renderer;
 pub use result::Result;
 pub use sandbox::Sandbox;
 pub use settings::Settings;
+pub use subscription::Subscription;
 pub use theme::Theme;
 
 pub use runtime::alignment;
 pub use runtime::futures;
 pub use runtime::{
     Alignment, Background, Color, Command, ContentFit, Font, Length, Padding,
-    Point, Rectangle, Size, Subscription, Vector,
+    Point, Rectangle, Size, Vector,
 };
 
 #[cfg(feature = "system")]

src/widget.rs

@@ -211,3 +211,14 @@ pub use qr_code::QRCode;
 #[cfg(feature = "svg")]
 #[cfg_attr(docsrs, doc(cfg(feature = "svg")))]
 pub use svg::Svg;
+
+use crate::Command;
+use iced_native::widget::operation;
+
+/// Focuses the next focusable widget.
+pub fn focus_next<Message>() -> Command<Message>
+where
+    Message: 'static,
+{
+    Command::widget(operation::focus_next())
+}