Allow to hook application window events

src/app.rs

@@ -2,6 +2,7 @@ use std::{cell::RefCell, rc::Rc, sync::Arc};
 
 use floem_reactive::WriteSignal;
 use floem_winit::{
+    event::WindowEvent,
     event_loop::{ControlFlow, EventLoop, EventLoopBuilder, EventLoopProxy},
     monitor::MonitorHandle,
     window::WindowId,
@@ -80,12 +81,13 @@ pub(crate) fn add_app_update_event(event: AppUpdateEvent) {
     });
 }
 
-/// Floem top level application
+/// Floem top level application.
 /// This is the entry point of the application.
 pub struct Application {
     handle: Option<ApplicationHandle>,
     event_listener: Option<Box<AppEventCallback>>,
     event_loop: EventLoop<UserEvent>,
+    custom_window_event_listener: Option<Box<dyn Fn(&WindowEvent) -> bool>>
 }
 
 impl Default for Application {
@@ -110,6 +112,7 @@ impl Application {
             handle: Some(handle),
             event_listener: None,
             event_loop,
+            custom_window_event_listener: None,
         }
     }
 
@@ -118,8 +121,16 @@ impl Application {
         self
     }
 
-    /// create a new window for the application, if you want multiple windows,
-    /// just chain more window method to the builder
+    /// Can be used to hook window events before they are handled by floem. Must return `true` if
+    /// the event was handled and the native floem event handling is not desired, or `false` to let
+    /// floem handle the event normally.
+    pub fn on_window_event(mut self, handle_event: impl Fn(&WindowEvent) -> bool + 'static) -> Self {
+        self.custom_window_event_listener = Some(Box::new(handle_event));
+        self
+    }
+
+    /// Create a new window for the application. If you want multiple windows, just chain more
+    /// `window()` methods to the builder.
     pub fn window<V: IntoView + 'static>(
         mut self,
         app_view: impl FnOnce(WindowId) -> V + 'static,
@@ -143,7 +154,13 @@ impl Application {
             match event {
                 floem_winit::event::Event::NewEvents(_) => {}
                 floem_winit::event::Event::WindowEvent { window_id, event } => {
-                    handle.handle_window_event(window_id, event, event_loop);
+                    let custom_handled = self.custom_window_event_listener
+                        .as_ref()
+                        .map(|handle_event| handle_event(&event))
+                        .unwrap_or(false);
+                    if !custom_handled {
+                        handle.handle_window_event(window_id, event, event_loop);
+                    }
                 }
                 floem_winit::event::Event::DeviceEvent { .. } => {}
                 floem_winit::event::Event::UserEvent(event) => {