SwiftUI 中的 Tabbar 中键实用功能

Question

我正在尝试重现一个“Instagram”，例如tabBar中间有一个“实用程序”按钮，不一定属于tabBar生态系统。

我附上了这个 gif 来显示我所追求的行为。来描述问题。中间的标签栏（黑色加号）是单击一个 ActionSheet，而不是切换视图。

我将如何在 UIKit 中做到这一点只是使用

override func tabBar(tabBar: UITabBar, didSelectItem item: UITabBarItem) {
    print("Selected item")
}

功能来自UITabBarDelegate. 但显然我们不能在 SwiftUI 中做到这一点，所以想看看人们是否尝试过任何想法。我最后的想法是简单地将它包装在 UIView 中并将它与 SwiftUI 一起使用，但我想避免这种情况并保持原生。

我在自定义 TabBar 中看到过一篇文章，但我想使用 Apple 提供的 TabBar 以避免将来出现任何差异。

谢谢！

编辑：使问题更清楚。

Answer 1

只需使用ZStack一个Button或任何您想要的视图即可...

struct MainTabView: View {

    @State private var selection = 0

    var body: some View {
        ZStack(alignment: .bottom) {
            TabView(selection: $selection) {
                ContentView()
                    .tabItem {
                        Label("Tab 1", systemImage: "list.dash")
                    }
                    .tag(0)

                ContentView()
                    .tabItem {
                        Label("Tab 2", systemImage: "list.dash")
                    }
                    .tag(1)
                
                Spacer()
                    .tabItem {
                        EmptyView()
                    }
                    .tag(2)
                
                ContentView()
                    .tabItem {
                        Label("Tab 3", systemImage: "square.and.pencil")
                    }
                    .tag(3)
                
                ContentView()
                    .tabItem {
                        Label("Tab 4", systemImage: "square.and.pencil")
                    }
                    .tag(4)
                
            }
            Button {
                
            } label: {
                Image(systemName: "plus")
                    .tint(Color.white)
            }
            .frame(width: 50, height: 50)
            .background(Color.green)
            .clipShape(Circle())
            
        }
        .ignoresSafeArea(.keyboard) // usefull so the button doesn't move around on keyboard show
        .onChange(of: selection) { [selection] newValue in
           if newValue == 2 { // replace 2 with your index
               self.selection = selection // reset the selection in case we somehow press the middle tab
           }
        }
    }
}

Answer 2

您可以引入新@State属性来存储所显示选项卡的旧标签。.onAppear { self.oldSelectedItem = self.selectedItem }并对除中间选项卡之外的每个选项卡执行下一个方法。中间的选项卡将负责显示操作表，其方法如下所示：

.onAppear { 
self.shouldShowActionSheet.toggle() 
self.selectedItem = self.oldSelectedItem
}

工作示例：

import SwiftUI

struct ContentView: View {
    @State private var selectedItem = 1
    @State private var shouldShowActionSheet = false
    @State private var oldSelectedItem = 1

    var body: some View {
        TabView (selection: $selectedItem) {
            Text("Home")
                .tabItem { Image(systemName: "house") }
                .tag(1)
                .onAppear { self.oldSelectedItem = self.selectedItem }
            Text("Search")
                .tabItem { Image(systemName: "magnifyingglass") }
                .tag(2)
                .onAppear { self.oldSelectedItem = self.selectedItem }
            Text("Add")
                .tabItem { Image(systemName: "plus.circle") }
                .tag(3)
                .onAppear {
                    self.shouldShowActionSheet.toggle()
                    self.selectedItem = self.oldSelectedItem
                }
            Text("Heart")
                .tabItem { Image(systemName: "heart") }
                .tag(4)
                .onAppear { self.oldSelectedItem = self.selectedItem }
            Text("Profile")
                .tabItem { Image(systemName: "person.crop.circle") }
                .tag(5)
                .onAppear { self.oldSelectedItem = self.selectedItem }
        }
        .actionSheet(isPresented: $shouldShowActionSheet) { ActionSheet(title: Text("Title"), message: Text("Message"), buttons: [.default(Text("Option 1"), action: option1), .default(Text("Option 2"), action: option2) , .cancel()]) }
    }

    func option1() {
        // do logic 1
    }

    func option2() {
        // do logic 2
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

Answer 3

感谢Aleskey的精彩回答（标记为正确）。除了围绕 Modal 写的一篇中等文章之外，我还对它进行了一些改进。我发现它有点不同

这是 jist。

MainTabBarData 是一个 Observable 对象

final class MainTabBarData: ObservableObject {

    /// This is the index of the item that fires a custom action
    let customActiontemindex: Int

    let objectWillChange = PassthroughSubject<MainTabBarData, Never>()

    var previousItem: Int

    var itemSelected: Int {
        didSet {
            if itemSelected == customActiontemindex {
                previousItem = oldValue
                itemSelected = oldValue
                isCustomItemSelected = true
            }
            objectWillChange.send(self)
        }
    }

    func reset() {
        itemSelected = previousItem
        objectWillChange.send(self)
    }

    /// This is true when the user has selected the Item with the custom action
    var isCustomItemSelected: Bool = false

    init(initialIndex: Int = 1, customItemIndex: Int) {
        self.customActiontemindex = customItemIndex
        self.itemSelected = initialIndex
        self.previousItem = initialIndex
    }
}

这是 TabbedView

struct TabbedView: View {

    @ObservedObject private var tabData = MainTabBarData(initialIndex: 1, customItemIndex: 2)


    var body: some View {

        TabView(selection: $tabData.itemSelected) {
            Text("First Screen")
                .tabItem {
                    VStack {
                        Image(systemName: "globe")
                            .font(.system(size: 22))
                        Text("Profile")
                    }

                }.tag(1)

            Text("Second Screen")
                .tabItem {
                    VStack {
                        Image(systemName: "plus.circle")
                            .font(.system(size: 22))
                        Text("Profile")
                    }
            }.tag(2)

            Text("Third Screen")
                .tabItem {
                    VStack {
                        Image(systemName: "number")
                            .font(.system(size: 22))
                        Text("Profile")
                    }
            }.tag(3)

        }.actionSheet(isPresented: $tabData.isCustomItemSelected) {
            ActionSheet(title: Text("SwiftUI ActionSheet"), message: Text("Action Sheet Example"),
                        buttons: [
                            .default(Text("Option 1"), action: option1),
                            .default(Text("Option 2"), action: option2),
                            .cancel(cancel)
                        ]
            )
        }



    }

    func option1() {
        tabData.reset()
        // ...
    }

    func option2() {
        tabData.reset()
        // ...
    }

    func cancel() {
        tabData.reset()
    }
}

struct TabbedView_Previews: PreviewProvider {
    static var previews: some View {
        TabbedView()
    }
}

类似的概念，只是利用了 SwiftUI 和 Combine 的强大功能。