在 SwiftUI 中通过摇动手势（使用 UIKit）设置 EnvironmentObject 不会更新视图
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【中文标题】在 SwiftUI 中通过摇动手势（使用 UIKit）设置 EnvironmentObject 不会更新视图【英文标题】：Setting EnvironmentObject from a Shake Gesture (using UIKit) in SwiftUI doesn't update View 【发布时间】：2020-02-10 19:57:43 【问题描述】：我希望通过物理摇晃设备来触发 SwiftUI 功能。由于此时 SwiftUI 还没有运动检测功能，所以我需要使用 UIKit 集成和协调器返回一个 Bool 值，该值表示设备已被晃动，从而触发 SwiftUI 功能。
以下代码在识别设备的晃动方面都非常有效（独立的“makeShakerSound()”函数证明了这一点，该函数在晃动时播放声音片段，效果很好）。除了识别抖动的工作代码之外，我还包括了用于从 ContentView 调用 ShakableViewRepresentable(isShaken: $shakeOccurred) 的代码，如下所示。
我创建了一个 EnvironmentObject 来标记设备已被摇动，并使用 objectWillChange 来宣布发生了变化。
我的问题是这样的：当检测到晃动时，晃动的声音效果很好，但是我的 ContentView 没有更新环境对象 myDevice.isShaken 的变化。我认为使用 objectWillChange 可能会解决这个问题，但事实并非如此。我错过了什么？
抱歉 - 我对此有点陌生。
/* CREATE AN ENVIRONMENTAL OBJECT TO INDICATE DEVICE HAS BEEN SHAKEN */
import Combine
import SwiftUI
class MyDevice: ObservableObject
// let objectWillChange = ObservableObjectPublisher()
var isShaken: Bool = false
willSet
self.objectWillChange.send()
/* DETECT SHAKE GESTURE AND FLAG THAT SHAKING HAS OCCURRED */
import UIKit
import SwiftUI
struct ShakableViewRepresentable: UIViewControllerRepresentable
class Coordinator: NSObject
var parent: ShakableViewRepresentable
init(_ parent: ShakableViewRepresentable)
self.parent = parent
func makeCoordinator() -> ShakableViewRepresentable.Coordinator
Coordinator(self)
func makeUIViewController(context: Context) -> ShakableViewController
ShakableViewController()
func updateUIViewController(_ uiViewController: ShakableViewController, context: Context)
class ShakableViewController: UIViewController
override func motionBegan(_ motion: UIEvent.EventSubtype, with event: UIEvent?)
guard motion == .motionShake else return
/* SHAKING GESTURE WAS DETECTED */
myDevice?.isShaken = true /* ContentView doesn't update! */
makeShakerSound() /* This works great */
/* I’M TRYING TO TRIGGER A FUNCTION IN SWIFTUI BY SHAKING THE DEVICE: Despite setting the myDevice.isShaken environment object to "true", my ContentView doesn't update when the shaking gesture is detected. */
ContentView.swift
@EnvironmentObject var myDevice: MyDevice
var body: some View
NavigationView
ZStack
/* DETECT SHAKE GESTURE - This works */
ShakableViewRepresentable()
.allowsHitTesting(false)
VStack
/* SHOW CURRENT STATE OF myDevice.isShaken - Doesn't update */
Text(self.myDevice.isShaken ? "The device has been shaken" : "No shaking has occurred")
Text("Device was shaken: \(self.myDevice.isShaken.description)")
/* more views below */
【问题讨论】：
【参考方案1】：例子
import SwiftUI
import Combine
class MyDevice: ObservableObject
//let objectWillChange = ObservableObjectPublisher()
var isShaken: Bool = false
willSet
self.objectWillChange.send()
struct ContentView: View
@ObservedObject var model = MyDevice()
var body: some View
VStack
Text("\(model.isShaken.description)").onTapGesture
self.model.isShaken.toggle()
struct ContentView_Previews: PreviewProvider
static var previews: some View
ContentView()
取消注释
let objectWillChange = ObservableObjectPublisher()
它停止工作。
不要重新定义你自己的 ObservableObjectPublisher()
检查
import SwiftUI
import Combine
class MyDevice: ObservableObject
//let objectWillChange = ObservableObjectPublisher()
var isShaken: Bool = false
willSet
self.objectWillChange.send()
struct ContentView: View
@EnvironmentObject var model: MyDevice
var body: some View
VStack
Text("\(model.isShaken.description)").onTapGesture
self.model.isShaken.toggle()
struct ContentView_Previews: PreviewProvider
static var previews: some View
ContentView().environmentObject(MyDevice())
在 SceneDelegate.swift 中
func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions)
// Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`.
// If using a storyboard, the `window` property will automatically be initialized and attached to the scene.
// This delegate does not imply the connecting scene or session are new (see `application:configurationForConnectingSceneSession` instead).
// Create the SwiftUI view that provides the window contents.
let contentView = ContentView().environmentObject(MyDevice())
//let contentView = ContentView()
// Use a UIHostingController as window root view controller.
if let windowScene = scene as? UIWindowScene
let window = UIWindow(windowScene: windowScene)
window.rootViewController = UIHostingController(rootView: contentView)
self.window = window
window.makeKeyAndVisible()
它按预期工作。
好的，使用震动检测器，
myDevice?.isShaken = true
永远不会运行，因为 myDevice 是 nil
解决办法
使您的模型全局可用，因为在 SwiftUI 中我们没有工具如何使其可用于 ShakableViewController，或者将其用作其 init 的参数
SwiftDelegate.swift
import UIKit
import SwiftUI
let model = MyDevice()
class SceneDelegate: UIResponder, UIWindowSceneDelegate
var window: UIWindow?
func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions)
// Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`.
// If using a storyboard, the `window` property will automatically be initialized and attached to the scene.
// This delegate does not imply the connecting scene or session are new (see `application:configurationForConnectingSceneSession` instead).
// Create the SwiftUI view that provides the window contents.
let contentView = ContentView().environmentObject(model)
//let contentView = ContentView()
// Use a UIHostingController as window root view controller.
if let windowScene = scene as? UIWindowScene
let window = UIWindow(windowScene: windowScene)
window.rootViewController = UIHostingController(rootView: contentView)
self.window = window
window.makeKeyAndVisible()
func sceneDidDisconnect(_ scene: UIScene)
// Called as the scene is being released by the system.
// This occurs shortly after the scene enters the background, or when its session is discarded.
// Release any resources associated with this scene that can be re-created the next time the scene connects.
// The scene may re-connect later, as its session was not neccessarily discarded (see `application:didDiscardSceneSessions` instead).
func sceneDidBecomeActive(_ scene: UIScene)
// Called when the scene has moved from an inactive state to an active state.
// Use this method to restart any tasks that were paused (or not yet started) when the scene was inactive.
func sceneWillResignActive(_ scene: UIScene)
// Called when the scene will move from an active state to an inactive state.
// This may occur due to temporary interruptions (ex. an incoming phone call).
func sceneWillEnterForeground(_ scene: UIScene)
// Called as the scene transitions from the background to the foreground.
// Use this method to undo the changes made on entering the background.
func sceneDidEnterBackground(_ scene: UIScene)
// Called as the scene transitions from the foreground to the background.
// Use this method to save data, release shared resources, and store enough scene-specific state information
// to restore the scene back to its current state.
ContentView.swift
import SwiftUI
import Combine
struct ShakableViewRepresentable: UIViewControllerRepresentable
class Coordinator: NSObject
var parent: ShakableViewRepresentable
init(_ parent: ShakableViewRepresentable)
self.parent = parent
func makeCoordinator() -> ShakableViewRepresentable.Coordinator
Coordinator(self)
func makeUIViewController(context: Context) -> ShakableViewController
ShakableViewController()
func updateUIViewController(_ uiViewController: ShakableViewController, context: Context)
class ShakableViewController: UIViewController
override func motionBegan(_ motion: UIEvent.EventSubtype, with event: UIEvent?)
guard motion == .motionShake else return
model.isShaken.toggle()
print(model.isShaken)
class MyDevice: ObservableObject
//let objectWillChange = ObservableObjectPublisher()
var isShaken: Bool = false
willSet
self.objectWillChange.send()
struct ContentView: View
@EnvironmentObject var model: MyDevice
var body: some View
VStack
ShakableViewRepresentable()
.allowsHitTesting(false)
Text(self.model.isShaken ? "The device has been shaken" : "No shaking has occurred").onTapGesture
self.model.isShaken.toggle()
struct ContentView_Previews: PreviewProvider
static var previews: some View
ContentView().environmentObject(MyDevice())
而且它可以工作，至少在我的设备上 :-)
没有声音，但会打印
true
false
true
false
true
每一次摇一摇的客串
【讨论】：
我注释掉了有问题的代码行。该应用程序编译并成功运行，但不幸的是结果相同 - 当 UIKit 中的摇动手势更新我的环境对象时，ContentView 仍未更新（mydevice?.isShaken = true）。 我也使用 EnvironmentObject 进行了检查...您是否将它暴露给您的 ContentView？ 这可能就是我所缺少的。正如我所说，我有点新手，所以如果我错过了一些基本的东西，我很抱歉。在上面的 ContentView 摘录中，我包括“@EnvironmentObject var myDevice: MyDevice”，以及一些调用 self.myDevice 的文本视图。对 myDevice 的更改是在 ShakableViewController: UIViewController 类中进行的（因为 soundFX 代码有效，所以它被成功调用）。我还需要将它暴露给 ContentView 吗？ 我更新了答案，看到这一行 let contentView = ContentView().environmentObject(MyDevice()) 别担心，更有经验的 SwiftUI 用户不知道它是如何工作的 :-) 一开始缺少（或非常不清楚）来自 Apple 的文档。以上是关于在 SwiftUI 中通过摇动手势（使用 UIKit）设置 EnvironmentObject 不会更新视图的主要内容，如果未能解决你的问题，请参考以下文章