Fix displayed to not assume UIViewController starts not displayed (#192)

* Fix `displayed` to not assume UIViewController starts not displayed

* Update changelog

Author: mgray88

CHANGELOG.md

@@ -1,3 +1,6 @@
+** *Unreleased* **:
+- fix: `displayed` and `rxVisible` now do not assume UIViewController starts not visible
+
 ** Version 2.13.0 **:
 
 - fix: use xcframeworks for RxFlow/RxFlowDemo deps to please Carthage

RxFlow/Extensions/Reactive+UIViewController.swift

@@ -31,8 +31,9 @@ public extension Reactive where Base: UIViewController {
     var displayed: Observable<Bool> {
         let viewDidAppearObservable = self.sentMessage(#selector(Base.viewDidAppear)).map { _ in true }
         let viewDidDisappearObservable = self.sentMessage(#selector(Base.viewDidDisappear)).map { _ in false }
-        // a UIViewController is at first not displayed
-        let initialState = Observable.just(false)
+        let initialState = Observable.deferred {
+            .just(base.viewIfLoaded?.window != nil)
+        }
         // future calls to viewDidAppear and viewDidDisappear will change the displayable state
         return initialState.concat(Observable<Bool>.merge(viewDidAppearObservable, viewDidDisappearObservable))
     }

RxFlowTests/UIViewController+PresentableTests.swift

@@ -42,6 +42,30 @@ final class UIViewController_PresentableTests: XCTestCase {
         }
     }
 
+    func testUIViewControllerVisibleStartsVisible() {
+        // Given: a UIViewController that starts "displayed"
+        let window = UIWindow()
+        let viewController = TestUIViewController()
+        _ = viewController.view
+        window.rootViewController = viewController
+        window.makeKeyAndVisible()
+        let testScheduler = TestScheduler(initialClock: 0)
+        let observer = testScheduler.createObserver(Bool.self)
+        testScheduler.start()
+
+        // When: subscribing to rxVisible
+        _ = viewController.rxVisible.asObservable().take(until: self.rx.deallocating).bind(to: observer)
+
+        // Then: rxVisible emits the first value as true
+        let referenceVisible = [true]
+        XCTAssertEqual(observer.events.count, 1)
+        var index = 0
+        referenceVisible.forEach {
+            XCTAssertEqual(observer.events[index].value.element, $0)
+            index += 1
+        }
+    }
+
     func testUIViewControllerDismissed() {
         // Given: a UIViewController
         let viewController = TestUIViewController()