Make eframe::App::as_any_mut optional to implement (#2061)

crates/eframe/CHANGELOG.md

@@ -12,6 +12,8 @@ NOTE: [`egui-winit`](../egui-winit/CHANGELOG.md), [`egui_glium`](../egui_glium/C
 * Added `shader_version` to `NativeOptions` for cross compiling support on different target OpenGL | ES versions (on native `glow` renderer only) ([#1993](https://github.com/emilk/egui/pull/1993)).
 * Fix: app state is now saved when user presses Cmd-Q on Mac ([#2013](https://github.com/emilk/egui/pull/2013)).
 * Added `center` to `NativeOptions` and `monitor_size` to `WindowInfo` on desktop ([#2035](https://github.com/emilk/egui/pull/2035)).
+* Web: you can access your application from JS using `AppRunner::app_mut`. See `crates/egui_demo_app/src/lib.rs`.
+
 
 ## 0.19.0 - 2022-08-20
 * MSRV (Minimum Supported Rust Version) is now `1.61.0` ([#1846](https://github.com/emilk/egui/pull/1846)).

crates/eframe/src/epi.rs

@@ -69,20 +69,25 @@ pub trait App {
     /// To force a repaint, call [`egui::Context::request_repaint`] at any time (e.g. from another thread).
     fn update(&mut self, ctx: &egui::Context, frame: &mut Frame);
 
-    /// Handle to the app.
+    /// Get a handle to the app.
     ///
-    /// Can be used from web to interact or other external context
-    /// Implementation is needed, because downcasting Box<dyn App> -> Box<dyn Any> to get &ConcreteApp is not simple in current rust.
+    /// Can be used from web to interact or other external context.
+    ///
+    /// You need to implement this if you want to be able to access the application from JS using [`AppRunner::app_mut`].
+    ///
+    /// This is needed because downcasting Box<dyn App> -> Box<dyn Any> to get &ConcreteApp is not simple in current rust.
     ///
     /// Just copy-paste this as your implementation:
     /// ```ignore
     /// #[cfg(target_arch = "wasm32")]
-    /// fn as_any_mut(&mut self) -> &mut dyn std::any::Any {
-    ///     &mut *self
+    /// fn as_any_mut(&mut self) -> Option<&mut dyn std::any::Any> {
+    ///     Some(&mut *self)
     /// }
     /// ```
     #[cfg(target_arch = "wasm32")]
-    fn as_any_mut(&mut self) -> &mut dyn Any;
+    fn as_any_mut(&mut self) -> Option<&mut dyn Any> {
+        None
+    }
 
     /// Called on shutdown, and perhaps at regular intervals. Allows you to save state.
     ///

crates/eframe/src/web/backend.rs

@@ -266,8 +266,14 @@ impl AppRunner {
     }
 
     /// Get mutable access to the concrete [`App`] we enclose.
+    ///
+    /// This will panic if your app does not implement [`App::as_any_mut`].
     pub fn app_mut<ConreteApp: 'static + crate::App>(&mut self) -> &mut ConreteApp {
-        self.app.as_any_mut().downcast_mut::<ConreteApp>().unwrap()
+        self.app
+            .as_any_mut()
+            .expect("Your app must implement `as_any_mut`, but it doesn't")
+            .downcast_mut::<ConreteApp>()
+            .unwrap()
     }
 
     pub fn auto_save(&mut self) {

crates/egui_demo_app/src/apps/custom3d_glow.rs

@@ -1,8 +1,5 @@
 use std::sync::Arc;
 
-#[cfg(target_arch = "wasm32")]
-use core::any::Any;
-
 use eframe::egui_glow;
 use egui::mutex::Mutex;
 use egui_glow::glow;
@@ -51,11 +48,6 @@ impl eframe::App for Custom3d {
             self.rotating_triangle.lock().destroy(gl);
         }
     }
-
-    #[cfg(target_arch = "wasm32")]
-    fn as_any_mut(&mut self) -> &mut dyn Any {
-        &mut *self
-    }
 }
 
 impl Custom3d {

crates/egui_demo_app/src/apps/custom3d_wgpu.rs

@@ -1,8 +1,5 @@
 use std::sync::Arc;
 
-#[cfg(target_arch = "wasm32")]
-use core::any::Any;
-
 use eframe::{
     egui_wgpu::{self, wgpu},
     wgpu::util::DeviceExt,
@@ -120,11 +117,6 @@ impl eframe::App for Custom3d {
                 });
         });
     }
-
-    #[cfg(target_arch = "wasm32")]
-    fn as_any_mut(&mut self) -> &mut dyn Any {
-        &mut *self
-    }
 }
 
 impl Custom3d {

crates/egui_demo_app/src/apps/http_app.rs

@@ -1,9 +1,6 @@
 use egui_extras::RetainedImage;
 use poll_promise::Promise;
 
-#[cfg(target_arch = "wasm32")]
-use core::any::Any;
-
 struct Resource {
     /// HTTP response
     response: ehttp::Response,
@@ -109,11 +106,6 @@ impl eframe::App for HttpApp {
             }
         });
     }
-
-    #[cfg(target_arch = "wasm32")]
-    fn as_any_mut(&mut self) -> &mut dyn Any {
-        &mut *self
-    }
 }
 
 fn ui_url(ui: &mut egui::Ui, frame: &mut eframe::Frame, url: &mut String) -> bool {

crates/egui_demo_app/src/wrap_app.rs

@@ -16,11 +16,6 @@ impl eframe::App for EasyMarkApp {
     fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
         self.editor.panels(ctx);
     }
-
-    #[cfg(target_arch = "wasm32")]
-    fn as_any_mut(&mut self) -> &mut dyn Any {
-        &mut *self
-    }
 }
 
 // ----------------------------------------------------------------------------
@@ -35,11 +30,6 @@ impl eframe::App for DemoApp {
     fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
         self.demo_windows.ui(ctx);
     }
-
-    #[cfg(target_arch = "wasm32")]
-    fn as_any_mut(&mut self) -> &mut dyn Any {
-        &mut *self
-    }
 }
 
 // ----------------------------------------------------------------------------
@@ -59,11 +49,6 @@ impl eframe::App for FractalClockApp {
                     .ui(ui, Some(crate::seconds_since_midnight()));
             });
     }
-
-    #[cfg(target_arch = "wasm32")]
-    fn as_any_mut(&mut self) -> &mut dyn Any {
-        &mut *self
-    }
 }
 
 // ----------------------------------------------------------------------------
@@ -88,11 +73,6 @@ impl eframe::App for ColorTestApp {
             });
         });
     }
-
-    #[cfg(target_arch = "wasm32")]
-    fn as_any_mut(&mut self) -> &mut dyn Any {
-        &mut *self
-    }
 }
 
 // ----------------------------------------------------------------------------
@@ -250,8 +230,8 @@ impl eframe::App for WrapApp {
     }
 
     #[cfg(target_arch = "wasm32")]
-    fn as_any_mut(&mut self) -> &mut dyn Any {
-        &mut *self
+    fn as_any_mut(&mut self) -> Option<&mut dyn Any> {
+        Some(&mut *self)
     }
 }
 

examples/custom_3d_three-d/src/main.rs

@@ -70,11 +70,6 @@ impl eframe::App for MyApp {
             });
         });
     }
-
-    #[cfg(target_arch = "wasm32")]
-    fn as_any_mut(&mut self) -> &mut dyn Any {
-        &mut *self
-    }
 }
 
 /// We get a [`glow::Context`] from `eframe` and we want to construct a [`ThreeDApp`].