Setup `to_do_mvc` for Android (#578)

I'm finding these cargo warnings exceptionally annoying...

.github/workflows/ci.yml

@@ -22,7 +22,7 @@ env:
   RUST_MIN_VER_WASM_PKGS: "-p xilem_core"
 
   # Only some of our examples support Android (primarily due to extra required boilerplate).
-  ANDROID_TARGETS: -p xilem --example mason_android --example calc_android --example stopwatch_android --example variable_clock_android
+  ANDROID_TARGETS: -p xilem --example mason_android --example calc_android --example stopwatch_android --example variable_clock_android --example http_cats_android --example to_do_mvc_android
 
   # We do not run the masonry snapshot tests, because those currently require a specific font stack
   # See https://github.com/linebender/xilem/pull/233

xilem/Cargo.toml

@@ -45,7 +45,6 @@ path = "examples/http_cats.rs"
 # cdylib is required for cargo-apk
 crate-type = ["cdylib"]
 
-
 [[example]]
 name = "stopwatch"
 
@@ -55,6 +54,15 @@ path = "examples/stopwatch.rs"
 # cdylib is required for cargo-apk
 crate-type = ["cdylib"]
 
+[[example]]
+name = "to_do_mvc"
+
+[[example]]
+name = "to_do_mvc_android"
+path = "examples/to_do_mvc.rs"
+# cdylib is required for cargo-apk
+crate-type = ["cdylib"]
+
 [[example]]
 name = "variable_clock"
 

xilem/examples/to_do_mvc.rs

@@ -4,8 +4,9 @@
 // On Windows platform, don't show a console when opening the app.
 #![windows_subsystem = "windows"]
 
-use xilem::view::{button, checkbox, flex, textbox, Axis};
-use xilem::{EventLoop, WidgetView, Xilem};
+use winit::error::EventLoopError;
+use xilem::view::{button, checkbox, flex, textbox, Axis, FlexSpacer};
+use xilem::{EventLoop, EventLoopBuilder, WidgetView, Xilem};
 
 struct Task {
     description: String,
@@ -66,12 +67,17 @@ fn app_logic(task_list: &mut TaskList) -> impl WidgetView<TaskList> {
         })
         .collect::<Vec<_>>();
 
-    flex((first_line, tasks))
+    flex((
+        FlexSpacer::Fixed(40.), // HACK: Spacer for Androird
+        first_line,
+        tasks,
+    ))
 }
 
-fn main() {
+fn run(event_loop: EventLoopBuilder) -> Result<(), EventLoopError> {
     let data = TaskList {
-        next_task: String::new(),
+        // Add a placeholder task for Android, whilst the
+        next_task: "My Next Task".into(),
         tasks: vec![
             Task {
                 description: "Buy milk".into(),
@@ -89,6 +95,38 @@ fn main() {
     };
 
     let app = Xilem::new(data, app_logic);
-    app.run_windowed(EventLoop::with_user_event(), "First Example".into())
-        .unwrap();
+    app.run_windowed(event_loop, "First Example".into())
+}
+
+// Boilerplate code for android: Identical across all applications
+
+#[cfg(not(target_os = "android"))]
+#[allow(dead_code)]
+// This is treated as dead code by the Android version of the example, but is actually live
+// This hackery is required because Cargo doesn't care to support this use case, of one
+// example which works across Android and desktop
+fn main() -> Result<(), EventLoopError> {
+    run(EventLoop::with_user_event())
+}
+
+#[cfg(target_os = "android")]
+// Safety: We are following `android_activity`'s docs here
+// We believe that there are no other declarations using this name in the compiled objects here
+#[allow(unsafe_code)]
+#[no_mangle]
+fn android_main(app: winit::platform::android::activity::AndroidApp) {
+    use winit::platform::android::EventLoopBuilderExtAndroid;
+
+    let mut event_loop = EventLoop::with_user_event();
+    event_loop.with_android_app(app);
+
+    run(event_loop).expect("Can create app");
+}
+
+// TODO: This is a hack because of how we handle our examples in Cargo.toml
+// Ideally, we change Cargo to be more sensible here?
+#[cfg(target_os = "android")]
+#[allow(dead_code)]
+fn main() {
+    unreachable!()
 }