Allow Sandbox applications to exit.

examples/exit/Cargo.toml

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+[package]
+name = "exit"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[dependencies]
+iced = { path = "../.." }

examples/exit/README.md

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+## Exit
+
+How to exit an application based on user input.
+
+The __[`main`]__ file contains all the code of the example.
+
+You can run it with `cargo run`:
+```
+cargo run --package exit
+```
+
+[`main`]: src/main.rs

examples/exit/src/main.rs

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+use iced::{
+    button, Alignment, Button, Column, Element, Sandbox, Settings, Text,
+};
+
+pub fn main() -> iced::Result {
+    Exit::run(Settings::default())
+}
+
+#[derive(Default)]
+struct Exit {
+    show_confirm: bool,
+    exit: bool,
+    confirm_button: button::State,
+    exit_button: button::State,
+}
+
+#[derive(Debug, Clone, Copy)]
+enum Message {
+    Confirm,
+    Exit,
+}
+
+impl Sandbox for Exit {
+    type Message = Message;
+
+    fn new() -> Self {
+        Self::default()
+    }
+
+    fn title(&self) -> String {
+        String::from("Exit - Iced")
+    }
+
+    fn should_exit(&self) -> bool {
+        self.exit
+    }
+
+    fn update(&mut self, message: Message) {
+        match message {
+            Message::Confirm => {
+                self.exit = true;
+            }
+            Message::Exit => {
+                self.show_confirm = true;
+            }
+        }
+    }
+
+    fn view(&mut self) -> Element<Message> {
+        if self.show_confirm {
+            Column::new()
+                .padding(20)
+                .align_items(Alignment::Center)
+                .push(Text::new("Are you sure you want to exit?"))
+                .push(
+                    Button::new(
+                        &mut self.confirm_button,
+                        Text::new("Yes, exit now"),
+                    )
+                    .on_press(Message::Confirm),
+                )
+                .into()
+        } else {
+            Column::new()
+                .padding(20)
+                .align_items(Alignment::Center)
+                .push(Text::new("Click the button to exit"))
+                .push(
+                    Button::new(&mut self.exit_button, Text::new("Exit"))
+                        .on_press(Message::Exit),
+                )
+                .into()
+        }
+    }
+}