Fix null window on initial HiDpiFactorChanged event on iOS (#1167)

CHANGELOG.md

@@ -11,6 +11,7 @@
 - Officially remove the Emscripten backend.
 - On Windows, fix handling of surrogate pairs when dispatching `ReceivedCharacter`.
 - On macOS 10.15, fix freeze upon exiting exclusive fullscreen mode.
+- On iOS, fix null window on initial `HiDpiFactorChanged` event.
 
 # 0.20.0 Alpha 3 (2019-08-14)
 

src/platform_impl/ios/view.rs

@@ -101,6 +101,7 @@ unsafe fn get_view_class(root_view_class: &'static Class) -> &'static Class {
         extern "C" fn draw_rect(object: &Object, _: Sel, rect: CGRect) {
             unsafe {
                 let window: id = msg_send![object, window];
+                assert!(!window.is_null());
                 app_state::handle_nonuser_event(Event::WindowEvent {
                     window_id: RootWindowId(window.into()),
                     event: WindowEvent::RedrawRequested,
@@ -116,6 +117,7 @@ unsafe fn get_view_class(root_view_class: &'static Class) -> &'static Class {
                 let () = msg_send![super(object, superclass), layoutSubviews];
 
                 let window: id = msg_send![object, window];
+                assert!(!window.is_null());
                 let bounds: CGRect = msg_send![window, bounds];
                 let screen: id = msg_send![window, screen];
                 let screen_space: id = msg_send![screen, coordinateSpace];
@@ -144,23 +146,24 @@ unsafe fn get_view_class(root_view_class: &'static Class) -> &'static Class {
                     setContentScaleFactor: untrusted_hidpi_factor
                 ];
 
-                // On launch, iOS sets the contentScaleFactor to 0.0. This is a sentinel value that
-                // iOS appears to use to "reset" the contentScaleFactor to the device specific
-                // default value.
-                //
-                // The workaround is to not trust the value received by this function, and always
-                // go through the getter.
+                let window: id = msg_send![object, window];
+                // `window` is null when `setContentScaleFactor` is invoked prior to `[UIWindow
+                // makeKeyAndVisible]` at window creation time (either manually or internally by
+                // UIKit when the `UIView` is first created), in which case we send no events here
+                if window.is_null() {
+                    return;
+                }
+                // `setContentScaleFactor` may be called with a value of 0, which means "reset the
+                // content scale factor to a device-specific default value", so we can't use the
+                // parameter here. We can query the actual factor using the getter
                 let hidpi_factor: CGFloat = msg_send![object, contentScaleFactor];
                 assert!(
                     !hidpi_factor.is_nan()
                         && hidpi_factor.is_finite()
                         && hidpi_factor.is_sign_positive()
                         && hidpi_factor > 0.0,
-                    "invalid hidpi_factor set on UIWindow",
+                    "invalid hidpi_factor set on UIView",
                 );
-
-                let window: id = msg_send![object, window];
-
                 let bounds: CGRect = msg_send![object, bounds];
                 let screen: id = msg_send![window, screen];
                 let screen_space: id = msg_send![screen, coordinateSpace];
@@ -186,6 +189,7 @@ unsafe fn get_view_class(root_view_class: &'static Class) -> &'static Class {
         extern "C" fn handle_touches(object: &Object, _: Sel, touches: id, _: id) {
             unsafe {
                 let window: id = msg_send![object, window];
+                assert!(!window.is_null());
                 let uiscreen: id = msg_send![window, screen];
                 let touches_enum: id = msg_send![touches, objectEnumerator];
                 let mut touch_events = Vec::new();

src/platform_impl/ios/window.rs

@@ -9,6 +9,7 @@ use objc::runtime::{Class, Object, BOOL, NO, YES};
 use crate::{
     dpi::{self, LogicalPosition, LogicalSize},
     error::{ExternalError, NotSupportedError, OsError as RootOsError},
+    event::{Event, WindowEvent},
     icon::Icon,
     monitor::MonitorHandle as RootMonitorHandle,
     platform::ios::{MonitorHandleExtIOS, ScreenEdge, ValidOrientations},
@@ -20,7 +21,7 @@ use crate::{
         },
         monitor, view, EventLoopWindowTarget, MonitorHandle,
     },
-    window::{CursorIcon, Fullscreen, WindowAttributes},
+    window::{CursorIcon, Fullscreen, WindowAttributes, WindowId as RootWindowId},
 };
 
 pub struct Inner {
@@ -377,6 +378,32 @@ impl Window {
                 },
             };
             app_state::set_key_window(window);
+
+            // Like the Windows and macOS backends, we send a `HiDpiFactorChanged` and `Resized`
+            // event on window creation if the DPI factor != 1.0
+            let hidpi_factor: CGFloat = msg_send![view, contentScaleFactor];
+            if hidpi_factor != 1.0 {
+                let bounds: CGRect = msg_send![view, bounds];
+                let screen: id = msg_send![window, screen];
+                let screen_space: id = msg_send![screen, coordinateSpace];
+                let screen_frame: CGRect =
+                    msg_send![view, convertRect:bounds toCoordinateSpace:screen_space];
+                let size = crate::dpi::LogicalSize {
+                    width: screen_frame.size.width as _,
+                    height: screen_frame.size.height as _,
+                };
+                app_state::handle_nonuser_events(
+                    std::iter::once(Event::WindowEvent {
+                        window_id: RootWindowId(window.into()),
+                        event: WindowEvent::HiDpiFactorChanged(hidpi_factor as _),
+                    })
+                    .chain(std::iter::once(Event::WindowEvent {
+                        window_id: RootWindowId(window.into()),
+                        event: WindowEvent::Resized(size),
+                    })),
+                );
+            }
+
             Ok(result)
         }
     }