小编Tir*_*rna的帖子

正如您从屏幕截图中看到的，“语言”选项卡出现了两次。

我有以下 HostingTabBar 代码，该代码在应用程序启动时调用：

struct HostingTabBar: View {
    
    private enum Tab: Hashable {
        case language
        case canvas
        case homework
        case test
        case more
    }
    
    @State private var selectedTab: Tab = .language
    
    var body: some View {
        TabView(selection: $selectedTab) {
        LanguageView()
            .tag(0)
            .tabItem {
                Text("Language")
                Image("language")
            }
        CanvasView()
            .tag(1)
            .tabItem {
                Text("Canvas")
                Image("canvas")
            }
        HomeworkView()
            .tag(2)
            .tabItem {
                Text("Homework")
                Image("homework")
            }
        TestView()
            .tag(3)
            .tabItem {
                Text("Test")
                Image("test")
            }
        MoreView()
            .tag(4)
            .tabItem {
                Text("More")
                Image("more")
            }
        }
        .accentColor(nil)
    }
}

struct HostingTabBar_Previews: …

我有以下代码：

import SwiftUI

struct LearnView: View {
    
    @State private var selectedLanguage: Language?
    @State private var selectedCategory: SubCategory?
    @State private var selectedDate = Date()
     
    @Environment(\.managedObjectContext) private var viewContext
    @FetchRequest(entity: Language.entity(), sortDescriptors: []) var languages: FetchedResults<Language>
    @FetchRequest(entity: SubCategory.entity(), sortDescriptors: []) var subCategories: FetchedResults<SubCategory>
    
    var body: some View {
        NavigationView {
            ZStack {
                Form {
                    Section("Learning Schedule") {
                        Picker("Please choose a language", selection: $selectedLanguage) {
                            ForEach(languages, id: \.self) {
                                Text($0.name ?? "Unknown")
                            }
                        }
                        Text("You selected: \(selectedLanguage?.name ?? "Unknown")")
                    }
                }
            }
        } …

我已经能够在我的应用程序的调试窗口中看到打印语句。当我创建一个“模拟”程序（小型试用应用程序）来了解 Swift 测试时，FirstTests 文件夹下的 LifecycleTests.swift 文件中的任何打印语句都不会显示在调试窗口中。

import XCTest

class LifecycleTests: XCTestCase {

    override class func setUp() {
        // Put setup code here. This method is called before the invocation of each test method in the class.
        print("In class setUp.")
        // NSLog("In class setUp.")
    }

    override class func tearDown() {
        // Put teardown code here. This method is called after the invocation of each test method in the class.
        print("In class tearDown.")
        // NSLog("In class tearDown")
    }

    override func setup() { …