问题描述
我正在使用 UIHostingController
将 ContentView
嵌入 ViewController
。我想在按下“更改名称”按钮时更改 ContentView
的 name
的名称。这是我的代码:
class ViewController: UIViewController {
var contentView: ContentView? /// keep reference to ContentView
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = UIColor.secondarySystemBackground
/// add the button
let button = UIButton()
button.frame = CGRect(x: 50,y: 50,width: 200,height: 100)
button.setTitle("Change name",for: .normal)
button.setTitleColor(.blue,for: .normal)
button.addTarget(self,action: #selector(handleTap),for: .touchUpInside)
view.addSubview(button)
/// add the SwiftUI ContentView
let contentView = ContentView()
let hostingController = UIHostingController(rootView: contentView)
self.contentView = contentView
addChild(hostingController)
view.insertSubview(hostingController.view,at: 0)
hostingController.view.frame = CGRect(x: 0,y: 400,width: view.bounds.width,height: view.bounds.height - 400)
hostingController.view.autoresizingMask = [.flexibleWidth,.flexibleHeight]
hostingController.didMove(toParent: self)
}
@objc func handleTap() {
contentView?.updateLastCardName(name: "Updated name") /// update the name
}
}
struct ContentView: View {
@State var name = "Name"
var body: some View {
Text(name)
}
func updateLastCardName(name: String) {
print("updating to \(name)")
self.name = name /// but it's not updating!
}
}
结果:
问题是,即使 func updateLastCardName(name: String) {
被调用,当我设置 self.name = name
时也没有变化。 Text
继续显示“名称”,而不是“更新的名称”。
我已经阅读了 @State
should be local,所以我尝试使用 updateLastCardName
函数解决这个问题。但是,它不起作用。我的方法有问题吗?
如何从ContentView
更新name
的{{1}}?
解决方法
var contentView: ContentView? /// keep reference to ContentView
这是错误的假设,因为 ContentView
是一个结构体,即。值,因此您保留副本而不是参考。
相反,我们应该使用视图模型类的实例作为从 UIKit 到 SwiftUI 通信的参考。在下面找到带有方法演示的修改代码。
使用 Xcode 12.4 / iOS 14.4 测试
class ViewModel: ObservableObject {
@Published var name = "Name"
}
class ViewController: UIViewController {
private var vm: ViewModel!
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = UIColor.secondarySystemBackground
/// add the button
let button = UIButton()
button.frame = CGRect(x: 50,y: 50,width: 200,height: 100)
button.setTitle("Change name",for: .normal)
button.setTitleColor(.blue,for: .normal)
button.addTarget(self,action: #selector(handleTap),for: .touchUpInside)
view.addSubview(button)
/// add the SwiftUI ContentView
self.vm = ViewModel()
let contentView = ContentView(vm: self.vm)
let hostingController = UIHostingController(rootView: contentView)
addChild(hostingController)
view.insertSubview(hostingController.view,at: 0)
hostingController.view.frame = CGRect(x: 0,y: 400,width: view.bounds.width,height: view.bounds.height - 400)
hostingController.view.autoresizingMask = [.flexibleWidth,.flexibleHeight]
hostingController.didMove(toParent: self)
}
@objc func handleTap() {
vm.name = "Updated name" /// update the name
}
}
struct ContentView: View {
@ObservedObject var vm: ViewModel
var body: some View {
Text(vm.name)
}
}