Fix Button actions and fg color on tvOS

Button actions weren't working at all on tvOS because
UIControl.Event.touchUpInside doesn't get triggered on
tvOS. Instead button interactions trigger
UIControl.Event.primaryActionTriggered. tvOS buttons
also have some weird foreground color stuff, see
comments I left in the code.

Author: stackotter

Sources/UIKitBackend/UIKitBackend+Control.swift

@@ -18,13 +18,16 @@ internal final class ButtonWidget: WrapperWidget<UIButton> {
 
     init() {
         let type: UIButton.ButtonType
+        let event: UIControl.Event
         #if os(tvOS)
             type = .system
+            event = .primaryActionTriggered
         #else
             type = .custom
+            event = .touchUpInside
         #endif
         super.init(child: UIButton(type: type))
-        child.addTarget(self, action: #selector(buttonTapped), for: .touchUpInside)
+        child.addTarget(self, action: #selector(buttonTapped), for: event)
     }
 }
 
@@ -221,11 +224,27 @@ extension UIKitBackend {
         environment: EnvironmentValues
     ) {
         let buttonWidget = button as! ButtonWidget
-        buttonWidget.child.setAttributedTitle(
-            UIKitBackend.attributedString(
-                text: label, environment: environment, defaultForegroundColor: .link),
-            for: .normal
-        )
+
+        // tvOS's buttons change foreground color when focused. If we set an
+        // attributed string for `.normal` we also have to set another for
+        // `.focused` with a colour that's readable on a white background.
+        // However, with that approach the label's color animates too slowly
+        // and all round looks quite sloppy. Therefore, it's safest to just
+        // ignore foreground color for buttons on tvOS until we have a better
+        // solution.
+        #if os(tvOS)
+            buttonWidget.child.setTitle(label, for: .normal)
+        #else
+            buttonWidget.child.setAttributedTitle(
+                UIKitBackend.attributedString(
+                    text: label,
+                    environment: environment,
+                    defaultForegroundColor: .link
+                ),
+                for: .normal
+            )
+        #endif
+
         buttonWidget.onTap = action
     }