eframe: allow aborting an exit event (#1038)

eframe/CHANGELOG.md

@@ -9,6 +9,7 @@ NOTE: [`egui_web`](egui_web/CHANGELOG.md), [`egui-winit`](egui-winit/CHANGELOG.m
 * The default native backend is now `egui_glow` (instead of `egui_glium`) ([#1020](https://github.com/emilk/egui/pull/1020)).
 * The default web painter is now `egui_glow` (instead of WebGL) ([#1020](https://github.com/emilk/egui/pull/1020)).
 * Fix horizontal scrolling direction on Linux.
+* Added `App::on_exit_event` ([#1038](https://github.com/emilk/egui/pull/1038))
 
 
 ## 0.16.0 - 2021-12-29

eframe/examples/confirm_exit.rs

@@ -0,0 +1,49 @@
+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")] // hide console window on Windows in release
+
+use eframe::{egui, epi};
+
+#[derive(Default)]
+struct MyApp {
+    can_exit: bool,
+    is_exiting: bool,
+}
+
+impl epi::App for MyApp {
+    fn name(&self) -> &str {
+        "Confirm exit"
+    }
+
+    fn on_exit_event(&mut self) -> bool {
+        self.is_exiting = true;
+        self.can_exit
+    }
+
+    fn update(&mut self, ctx: &egui::Context, frame: &epi::Frame) {
+        egui::CentralPanel::default().show(ctx, |ui| {
+            ui.heading("Try to close the window");
+        });
+
+        if self.is_exiting {
+            egui::Window::new("Do you want to quit?")
+                .collapsible(false)
+                .resizable(false)
+                .show(ctx, |ui| {
+                    ui.horizontal(|ui| {
+                        if ui.button("Yes!").clicked() {
+                            self.can_exit = true;
+                            frame.quit();
+                        }
+
+                        if ui.button("Not yet").clicked() {
+                            self.is_exiting = false;
+                        }
+                    });
+                });
+        }
+    }
+}
+
+fn main() {
+    let options = eframe::NativeOptions::default();
+    eframe::run_native(Box::new(MyApp::default()), options);
+}