Save state on suspend on Android and iOS

crates/eframe/src/native/glow_integration.rs

@@ -366,6 +366,25 @@ impl<'app> WinitApp for GlowWinitApp<'app> {
             .and_then(|r| r.glutin.borrow().window_from_viewport.get(&id).copied())
     }
 
+    fn save(&mut self) {
+        log::debug!("WinitApp::save called");
+        if let Some(running) = self.running.as_mut() {
+            profiling::function_scope!();
+
+            // This is used because of the "save on suspend" logic on Android. Once the application is suspended, there is no window associated to it, which was causing panics when `.window().expect()` was used.
+            let window_opt = running.glutin.borrow().window_opt(ViewportId::ROOT);
+            if window_opt.is_some() {
+                log::debug!("Saving application state with a window");
+            } else {
+                log::debug!("Saving application state without a window");
+            }
+
+            running
+                .integration
+                .save(running.app.as_mut(), window_opt.as_deref());
+        }
+    }
+
     fn save_and_destroy(&mut self) {
         if let Some(mut running) = self.running.take() {
             profiling::function_scope!();
@@ -413,6 +432,12 @@ impl<'app> WinitApp for GlowWinitApp<'app> {
         if let Some(running) = &mut self.running {
             running.glutin.borrow_mut().on_suspend()?;
         }
+        #[cfg(target_os = "android")]
+        {
+            log::debug!("Android application suspended - asking to save state");
+            Ok(EventResult::Save)
+        }
+        #[cfg(not(target_os = "android"))]
         Ok(EventResult::Wait)
     }
 
@@ -1214,10 +1239,12 @@ impl GlutinWindowContext {
             .expect("viewport doesn't exist")
     }
 
+    fn window_opt(&self, viewport_id: ViewportId) -> Option<Arc<Window>> {
+        self.viewport(viewport_id).window.clone()
+    }
+
     fn window(&self, viewport_id: ViewportId) -> Arc<Window> {
-        self.viewport(viewport_id)
-            .window
-            .clone()
+        self.window_opt(viewport_id)
             .expect("winit window doesn't exist")
     }
 

crates/eframe/src/native/run.rs

@@ -89,6 +89,7 @@ impl<T: WinitApp> WinitAppWrapper<T> {
         event_result: Result<EventResult>,
     ) {
         let mut exit = false;
+        let mut save = false;
 
         log::trace!("event_result: {event_result:?}");
 
@@ -126,6 +127,10 @@ impl<T: WinitApp> WinitAppWrapper<T> {
                     );
                     Ok(event_result)
                 }
+                EventResult::Save => {
+                    save = true;
+                    Ok(event_result)
+                }
                 EventResult::Exit => {
                     exit = true;
                     Ok(event_result)
@@ -139,6 +144,11 @@ impl<T: WinitApp> WinitAppWrapper<T> {
             self.return_result = Err(err);
         };
 
+        if save {
+            log::debug!("Received an EventResult::Save - saving app state");
+            self.winit_app.save();
+        }
+
         if exit {
             if self.run_and_return {
                 log::debug!("Asking to exit event loop…");

crates/eframe/src/native/wgpu_integration.rs

@@ -355,6 +355,13 @@ impl<'app> WinitApp for WgpuWinitApp<'app> {
         )
     }
 
+    fn save(&mut self) {
+        log::debug!("WinitApp::save called");
+        if let Some(running) = self.running.as_mut() {
+            running.save(true);
+        }
+    }
+
     fn save_and_destroy(&mut self) {
         if let Some(mut running) = self.running.take() {
             running.save_and_destroy();
@@ -414,7 +421,12 @@ impl<'app> WinitApp for WgpuWinitApp<'app> {
 
     fn suspended(&mut self, _: &ActiveEventLoop) -> crate::Result<EventResult> {
         #[cfg(target_os = "android")]
-        self.drop_window()?;
+        {
+            log::debug!("Android application suspended - asking to save state");
+            self.drop_window()?;
+            Ok(EventResult::Save)
+        }
+        #[cfg(not(target_os = "android"))]
         Ok(EventResult::Wait)
     }
 
@@ -488,20 +500,31 @@ impl<'app> WinitApp for WgpuWinitApp<'app> {
 }
 
 impl<'app> WgpuWinitRunning<'app> {
-    fn save_and_destroy(&mut self) {
-        profiling::function_scope!();
-
-        let mut shared = self.shared.borrow_mut();
+    /// Saves the application state. Set `force_save_without_window` to `true` if the state should be saved even if no window is associated to the application (this happens on Android when the `suspended` event is received).
+    fn save(&mut self, force_save_without_window: bool) {
+        let shared = self.shared.borrow();
+        // This is done because of the "save on suspend" logic on Android. Once the application is suspended, there is no window associated to it.
         if let Some(Viewport { window, .. }) = shared.viewports.get(&ViewportId::ROOT) {
+            log::debug!("Saving application state with a window");
             self.integration.save(self.app.as_mut(), window.as_deref());
+        } else if force_save_without_window {
+            log::debug!("Saving application state without a window");
+            self.integration.save(self.app.as_mut(), None);
         }
+    }
+
+    fn save_and_destroy(&mut self) {
+        profiling::function_scope!();
+
+        self.save(false);
 
         #[cfg(feature = "glow")]
         self.app.on_exit(None);
 
         #[cfg(not(feature = "glow"))]
         self.app.on_exit();
 
+        let mut shared = self.shared.borrow_mut();
         shared.painter.destroy();
     }
 

crates/eframe/src/native/winit_integration.rs

@@ -70,6 +70,8 @@ pub trait WinitApp {
 
     fn window_id_from_viewport_id(&self, id: ViewportId) -> Option<WindowId>;
 
+    fn save(&mut self);
+
     fn save_and_destroy(&mut self);
 
     fn run_ui_and_paint(
@@ -119,6 +121,10 @@ pub enum EventResult {
 
     RepaintAt(WindowId, Instant),
 
+    /// Causes a save of the client state when the persistence feature is enabled.
+    #[allow(dead_code)] // Not used outside of Android
+    Save,
+
     Exit,
 }