Found nil while getting JSON data

Question

I don't know why there's nil on the JSON structure. Below is the code. The structure is relatively simple, but somehow I just can't parse the decoded JSON.

ContentView.swift

import SwiftUI
var fetchTotal = getTotalValue()
struct ContentView: View {

var body: some View {
   Text(fetchTotal)
    //Text("gg")
   }
}

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

Decoded_structure.swift:

import Foundation
import SwiftUI

struct PostTotal: Codable {
var rows: [Layer0]
struct Layer0: Codable, Hashable {

    var totalmarketvalue: String
    var totaltodaysprofit: String
    var todaysprofitpercent: String
    var totalasset: String
    var maxpurchasepower: String

  }
}
   let webstringtotal: String = "http://gsx2json.com/api?id=1z9WvS25hDvLaNPX1HwTE-CiJ46UvmqlUWT-iWVT0aJY&sheet=1&integers=false&column=false"


 func getTotalValue() -> String {
 let urlTotal = URL(string: webstringtotal)
 var results: String = ""
    URLSession.shared.dataTask(with: urlTotal!) { (datas, _, _) in
        let postss = try! JSONDecoder().decode([PostTotal.Layer0].self, from: datas!)
        //let layer0 = [postss.rows]
        results = postss[0].totalasset
}
.resume()
return results

}

And the error message:

2020-06-11 15:51:46.211463+0800 PureTestProject[28884:988078] [Agent] Received remote injection
2020-06-11 15:51:46.211753+0800 PureTestProject[28884:988078] [Agent] Create remote injection Mach transport: 600001500770
2020-06-11 15:51:46.212150+0800 PureTestProject[28884:988022] [Agent] No global connection handler, using shared user agent
2020-06-11 15:51:46.212339+0800 PureTestProject[28884:988022] [Agent] Received connection, creating agent
2020-06-11 15:51:46.897118+0800 PureTestProject[28884:988022] [Agent] Received message: < DTXMessage 0x600001a150e0 : i2.0e c0 object:(__NSDictionaryI*) {
    "products" : <NSArray 0x600003c141b0 | 1 objects>
    "id" : [0]
    "scaleFactorHint" : [3]
    "providerName" : "15PureTestProject20ContentView_PreviewsV"
    "updates" : <NSArray 0x7fff8062d430 | 0 objects>
} > {
    "serviceCommand" : "forwardMessage"
    "type" : "display"
}
2020-06-11 15:51:46.938191+0800 PureTestProject[28884:988035] App Transport Security has blocked a cleartext HTTP (http://) resource load since it is insecure. Temporary exceptions can be configured via your app's Info.plist file.
2020-06-11 15:51:46.938349+0800 PureTestProject[28884:988035] Cannot start load of Task <EF8F8A3E-E1FC-4E80-808A-1B576BBCDBD6>.<1> since it does not conform to ATS policy
2020-06-11 15:51:46.940051+0800 PureTestProject[28884:988033] Task <EF8F8A3E-E1FC-4E80-808A-1B576BBCDBD6>.<1> finished with error [-1022] Error Domain=NSURLErrorDomain Code=-1022 "The resource could not be loaded because the App Transport Security policy requires the use of a secure connection." UserInfo={NSUnderlyingError=0x6000030045d0 {Error Domain=kCFErrorDomainCFNetwork Code=-1022 "(null)"}, NSErrorFailingURLStringKey=http://gsx2json.com/api?id=1z9WvS25hDvLaNPX1HwTE-CiJ46UvmqlUWT-iWVT0aJY&sheet=1&integers=false&column=false, NSErrorFailingURLKey=http://gsx2json.com/api?id=1z9WvS25hDvLaNPX1HwTE-CiJ46UvmqlUWT-iWVT0aJY&sheet=1&integers=false&column=false, NSLocalizedDescription=The resource could not be loaded because the App Transport Security policy requires the use of a secure connection.}
Fatal error: Unexpectedly found nil while unwrapping an Optional value: file /Users/benny/temp_files/test_xcode_11/PureTestProject/PureTestProject/Decoded_struct.swift, line 31
2020-06-11 15:51:46.957521+0800 PureTestProject[28884:988033] Fatal error: Unexpectedly found nil while unwrapping an Optional value: file /Users/benny/temp_files/test_xcode_11/PureTestProject/PureTestProject/Decoded_struct.swift, line 31
    (lldb)

Answer 1

the error says that you are connecting using http:// . Apple does not like this, it expect https:// . But you can provide an exception in the info.plist to get around this. Because of this your "datas" is nil, and as mentioned you are trying to unwrap it, triggering the error message.

Here is one example to put into info.plist:

<key>NSAppTransportSecurity</key>
<dict>
<key>NSAllowsArbitraryLoads</key>
<true/>
<key>NSExceptionDomains</key>
<dict>
    <key>example.com</key>
    <dict>
        <key>NSExceptionAllowsInsecureHTTPLoads</key>
        <true/>
        <key>NSIncludesSubdomains</key>
        <true/>
    </dict>
</dict>
</dict>

Edit: the code I use for testing, updated with an async example:

import Foundation
import SwiftUI

struct ContentView: View {
@State var results: PostTotal?

var body: some View {
    VStack (alignment: .leading) {
        Text("totalasset: \(results?.rows[0].totalasset ?? " fetching data ...") ")
        Text("maxpurchasepower: \(results?.rows[0].maxpurchasepower ?? " fetching data ..." )")
    }.onAppear(perform: loadData)
}

func loadData() {
    getTotalValue() { res in
        self.results = res
    }
}
}

struct PostTotal: Codable {
var columns: Layer1
var rows: [Layer0]

 struct Layer0: Codable, Hashable {
     var totalmarketvalue: String
     var totaltodaysprofit: String
     var todaysprofitpercent: String
     var totalasset: String
     var maxpurchasepower: String
 }

struct Layer1: Codable, Hashable {
    var totalmarketvalue: [String]
    var totaltodaysprofit: [String]
    var todaysprofitpercent: [String]
    var totalasset: [String]
    var maxpurchasepower:[String]
}
}

let webstringtotal: String = "http://gsx2json.com/api?id=1z9WvS25hDvLaNPX1HwTE-CiJ46UvmqlUWT-iWVT0aJY&sheet=1&integers=false&column=false"

func getTotalValue(handler: @escaping (PostTotal?) -> Void) {
let urlTotal = URL(string: webstringtotal)
URLSession.shared.dataTask(with: urlTotal!) { (datas, _, _) in
    if let theData = datas, let postss = try? JSONDecoder().decode(PostTotal.self, from: theData) {
        return handler(postss)
    } else {
        return handler(nil)
    }
}
.resume()
}