Enable to build it for iOS 12

Author: scenee

Examples/SamplesSwiftUI/SamplesSwiftUI/UseCases/MainView.swift

@@ -3,6 +3,7 @@
 import FloatingPanel
 import SwiftUI
 import UIKit
+import os.log
 
 struct MainView: View {
     @State private var panelLayout: FloatingPanelLayout? = MyFloatingPanelLayout()
@@ -20,6 +21,9 @@ struct MainView: View {
                 .floatingPanelSurfaceAppearance(.transparent())
                 .floatingPanelLayout(panelLayout)
                 .floatingPanelState($panelState)
+                .onChange(of: panelState) { newValue in
+                    Logger().debug("Panel state changed: \(newValue ?? .hidden)")
+                }
 
             VStack(spacing: 32) {
                 Button("Move to full") {

FloatingPanel.xcodeproj/project.pbxproj

@@ -523,7 +523,7 @@
 				ENABLE_USER_SCRIPT_SANDBOXING = YES;
 				INFOPLIST_FILE = Sources/Info.plist;
 				INSTALL_PATH = "$(LOCAL_LIBRARY_DIR)/Frameworks";
-				IPHONEOS_DEPLOYMENT_TARGET = 13.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 12.0;
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",
 					"@executable_path/Frameworks",
@@ -556,7 +556,7 @@
 				ENABLE_USER_SCRIPT_SANDBOXING = YES;
 				INFOPLIST_FILE = Sources/Info.plist;
 				INSTALL_PATH = "$(LOCAL_LIBRARY_DIR)/Frameworks";
-				IPHONEOS_DEPLOYMENT_TARGET = 13.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 12.0;
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",
 					"@executable_path/Frameworks",
@@ -694,7 +694,7 @@
 				ENABLE_USER_SCRIPT_SANDBOXING = YES;
 				INFOPLIST_FILE = Sources/Info.plist;
 				INSTALL_PATH = "$(LOCAL_LIBRARY_DIR)/Frameworks";
-				IPHONEOS_DEPLOYMENT_TARGET = 13.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 12.0;
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",
 					"@executable_path/Frameworks",

Sources/Core.swift

@@ -1,6 +1,8 @@
 // Copyright 2018-Present Shin Yamamoto. All rights reserved. MIT license.
 
+#if canImport(Combine)
 import Combine
+#endif
 import UIKit
 import os.log
 
@@ -50,7 +52,13 @@ class Core: NSObject, UIGestureRecognizerDelegate {
             }
         }
     }
-    private(set) var statePublisher: CurrentValueSubject<FloatingPanelState, Never> = .init(.hidden)
+
+    @available(iOS 13.0, *)
+    private(set) var statePublisher: CurrentValueSubject<FloatingPanelState, Never>? {
+        get { _statePublisher as? CurrentValueSubject<FloatingPanelState, Never> }
+        set { _statePublisher = newValue }
+    }
+    private var _statePublisher: Any?
 
     var panGestureRecognizer: FloatingPanelPanGestureRecognizer
     let panGestureDelegateRouter: FloatingPanelPanGestureRecognizer.DelegateRouter
@@ -100,6 +108,10 @@ class Core: NSObject, UIGestureRecognizerDelegate {
 
         super.init()
 
+        if #available(iOS 13.0, *) {
+            statePublisher = .init(.hidden)
+        }
+
         panGestureRecognizer.set(floatingPanel: self)
         surfaceView.addGestureRecognizer(panGestureRecognizer)
         panGestureRecognizer.addTarget(self, action: #selector(handle(panGesture:)))
@@ -262,7 +274,9 @@ class Core: NSObject, UIGestureRecognizerDelegate {
         layoutAdapter.activateLayout(for: target, forceLayout: true)
         backdropView.alpha = getBackdropAlpha(for: target)
         adjustScrollContentInsetIfNeeded()
-        statePublisher.send(target)
+        if #available(iOS 13.0, *) {
+            statePublisher?.send(target)
+        }
     }
 
     private func getBackdropAlpha(for target: FloatingPanelState) -> CGFloat {

Sources/SwiftUI/FloatingPanelView.swift

@@ -235,7 +235,7 @@ extension FloatingPanelCoordinatorProxy {
 
     /// Start observing ``FloatingPanelController/state`` through the `Core` object.
     func observeStateChanges() {
-        controller.floatingPanel.statePublisher
+        controller.floatingPanel.statePublisher?
             .sink { [weak self] state in
                 guard let self = self else { return }
                 // Needs to update the state binding value on the next run loop cycle to avoid this error.