Add basic IME support for Android

src/changelog/v0.30.md

@@ -1,3 +1,10 @@
+
+## 0.30.13
+
+### Added
+
+- On Android, added support for Ime events, for soft keyboard input.
+
 ## 0.30.12
 
 ### Fixed

src/event.rs

@@ -227,7 +227,7 @@ pub enum WindowEvent {
     ///
     /// ## Platform-specific
     ///
-    /// - **iOS / Android / Web / Orbital:** Unsupported.
+    /// - **iOS / Web / Orbital:** Unsupported.
     Ime(Ime),
 
     /// The cursor has moved on the window.

src/platform_impl/android/mod.rs

@@ -6,7 +6,9 @@ use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{mpsc, Arc, Mutex};
 use std::time::{Duration, Instant};
 
-use android_activity::input::{InputEvent, KeyAction, Keycode, MotionAction};
+use android_activity::input::{
+    InputEvent, KeyAction, Keycode, MotionAction, TextInputState, TextSpan,
+};
 use android_activity::{
     AndroidApp, AndroidAppWaker, ConfigurationRef, InputStatus, MainEvent, Rect,
 };
@@ -466,6 +468,31 @@ impl<T: 'static> EventLoop<T> {
                     },
                 }
             },
+            InputEvent::TextEvent(ime_state) => {
+                // Note: Winit does not support surrounding text or tracking a selection/cursor that
+                // may span within the surrounding text and the preedit text.
+                //
+                // Since there's no API to specify surrounding text, set_ime_allowed() will reset
+                // the text to an empty string and we will treat all the text as preedit text.
+                //
+                // We map Android's composing region to winit's preedit selection region.
+                //
+                // This seems a little odd, since Android's notion of a "composing region" would
+                // normally be equated with winit's "preedit" text but conceptually we're mapping
+                // Android's surrounding text + composing region into winit's preedit text +
+                // selection region.
+                //
+                // We ignore the separate selection region that Android supports.
+                let event = event::Event::WindowEvent {
+                    window_id: window::WindowId(WindowId),
+                    event: event::WindowEvent::Ime(event::Ime::Preedit(
+                        ime_state.text.clone(),
+                        ime_state.compose_region.map(|span| (span.start, span.end)),
+                    )),
+                };
+
+                callback(event, self.window_target());
+            },
             _ => {
                 warn!("Unknown android_activity input event {event:?}")
             },
@@ -770,6 +797,7 @@ pub struct PlatformSpecificWindowAttributes;
 pub(crate) struct Window {
     app: AndroidApp,
     redraw_requester: RedrawRequester,
+    ime_allowed: AtomicBool,
 }
 
 impl Window {
@@ -779,7 +807,11 @@ impl Window {
     ) -> Result<Self, error::OsError> {
         // FIXME this ignores requested window attributes
 
-        Ok(Self { app: el.app.clone(), redraw_requester: el.redraw_requester.clone() })
+        Ok(Self {
+            app: el.app.clone(),
+            redraw_requester: el.redraw_requester.clone(),
+            ime_allowed: AtomicBool::new(false),
+        })
     }
 
     pub(crate) fn maybe_queue_on_main(&self, f: impl FnOnce(&Self) + Send + 'static) {
@@ -909,11 +941,24 @@ impl Window {
     pub fn set_ime_cursor_area(&self, _position: Position, _size: Size) {}
 
     pub fn set_ime_allowed(&self, allowed: bool) {
+        // Request a show/hide regardless of whether the state has changed, since
+        // the keyboard may have been dismissed by the user manually while in the
+        // middle of text input
         if allowed {
             self.app.show_soft_input(true);
         } else {
             self.app.hide_soft_input(true);
         }
+
+        if self.ime_allowed.swap(allowed, Ordering::SeqCst) == allowed {
+            return;
+        }
+
+        self.app.set_text_input_state(TextInputState {
+            text: String::new(),
+            selection: TextSpan { start: 0, end: 0 },
+            compose_region: None,
+        });
     }
 
     pub fn set_ime_purpose(&self, _purpose: ImePurpose) {}