How can I solve that cannot preview in this file?

Question

I'm currently developing an application using SwiftUI.

I can build these codes successfully and these work well in a simulator.

But when I see a preview of the code on a canvas, the preview doesn't work, and there is an error message below:

Cannot preview in this file - My.app may have crashed

In this case, How can I solve this error and see the preview on the canvas?

Here are the codes:

I can't see previews of FirstView.swift and SecondView.swift

ContentView.swift

import SwiftUI

struct ContentView: View {
    
    @ObservedObject var viewModel = ViewModel()
    
    var body: some View {
        TabView {
            FirstView()
                .tabItem {
                    Text("First")
            }.tag(1)

            SecondView()
                .tabItem {
                    Text("Second")
            }.tag(2)
        }
        .environmentObject(viewModel)
    }
}

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

FirstView.swift

import SwiftUI

struct FirstView: View {

    @EnvironmentObject var firstCheck: ViewModel
    
    var body: some View {
        VStack{
            if firstCheck.check == true{
                    Text("checked")
            }
        }
    }
}

struct FirstView_Previews: PreviewProvider {
    static var previews: some View {
        FirstView()
    }
}

SecondView.swift

import SwiftUI

struct SecondView: View {

@EnvironmentObject var secondCheck: ViewModel

    var body: some View {
        VStack{
            Toggle(
                isOn: $secondCheck.check
            ){
                Text("change")
            }
            if self.secondCheck.check == true{
                Text("checked")
            }
        }
    }
}

struct SecondView_Previews: PreviewProvider {
    static var previews: some View {
        SecondView()
    }
}

ViewModel.swift

import Foundation

final class ViewModel: ObservableObject {
    @Published var check: Bool = false
}

Xcode: Version 11.7

Swift: Swift 5

pawello2222 pawello2222 · Accepted Answer · 2020-09-03T14:37:56

Your views need the @EnvironmentObject even in previews:

struct FirstView_Previews: PreviewProvider {
    static var previews: some View {
        FirstView()
            .environmentObject(ViewModel())
    }
}

struct SecondView_Previews: PreviewProvider {
    static var previews: some View {
        SecondView()
            .environmentObject(ViewModel())
    }
}

How can I solve that cannot preview in this file?

1 Answers