iam working with swiftui for the first time. iam trying to make a small social network app, so i created a navigation bar which lays over the other views to navigate between them. But when iam trying to creat a Preview a Problem screen pops up, when iam running the app in the simulator everything work fine. enter image description here

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enter image description here

CodePudding user response：

Your NavigationBar view needs to receive an @EnvironmentObject, also from the preview.

Inside your NavigationBar_Previews, add one more modifier to the view, like this:

NavigationBar()
    .environmentObject(AppInformation())   // Add all initialisers necessary
                                           // to create the instance of AppInformation()

CodePudding user response：

import SwiftUI

struct NavigationBar: View {

@EnvironmentObject var appInfo: AppInformation

var body: some View {
    
    ZStack
    {
Capsule()
    .frame(width: 400, height: 70)
    .foregroundColor(.blue)
    .overlay(
        
        HStack(spacing: 10) {
            ZStack{
                Image(systemName:  self.appInfo.home ? "house.fill" : "house")
                .resizable()
                .frame(width: 30, height: 28)
                .foregroundColor(.white)
                .padding(5)
                
                Button("   ") {
                    appInfo.home = true
                    appInfo.camera = false
                    appInfo.friends = false
                    appInfo.profil = false
                }
                .frame(width: 35, height: 35)
              }
            
            Spacer()
                .frame(width: 30)
            
            ZStack {
                Image(systemName: self.appInfo.camera ? "camera.fill" : "camera")
                    .resizable()
                    .frame(width: 30, height: 25)
                    .foregroundColor(.white)
                    .padding(5)
                
                Button("    ") {
                    appInfo.home = false
                    appInfo.camera = true
                    appInfo.friends = false
                    appInfo.profil = false
                    
                }
                .frame(width: 35, height: 35)
            }
            
            Spacer()
                .frame(width: 30)
            
            ZStack {
                Image(systemName: self.appInfo.friends ? "person.3.fill" : "person.3")
                    .resizable()
                    .frame(width: 35, height: 30)
                    .foregroundColor(.white)
                    .padding()
                
                Button("    ") {
                    appInfo.home = false
                    appInfo.camera = false
                    appInfo.friends = true
                    appInfo.profil = false
                }
                .frame(width: 35, height: 35)
            }
            
            Spacer()
                .frame(width: 30)
            
            ZStack {
                Image(systemName: self.appInfo.profil ? "person.fill" : "person")
                    .resizable()
                    .frame(width: 30, height: 30)
                    .foregroundColor(.white)
                    .padding(5)
                
                Button("    ") {
                    appInfo.home = false
                    appInfo.camera = false
                    appInfo.friends = false
                    appInfo.profil = true
                }
                .frame(width: 35, height: 35)
            }
        }
      )
    }
    .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .bottom)
}

}