UIApplication applicationState must be used from main thread only

Question

I am trying to do some unit testing for the API. Here is the actual function.

 func registerApi(path: String, player_id: Int, contest_id: Int, country_id: Int,  success: () -> Void)
{
    ServiceHelper.sharedInstance.sendRequest(path: "register-country",
                                             params: ["api_token": Constants.USER_INFO["api_token"].rawValue,
                                                      "player_id": player_id,
                                                      "country_id": country_id,
                                                      "contest_id": contest_id],
                                             showSpinner: true,
                                             completionHandler:
        { (response, error) in

            if (error != nil)
            {
             Test to be failed
            }
            else
            {
                Test Passed

            }
    })
}

And, now here is the test function for unit testing.

func testApiWorking()
{
    let controller = WorldCupChooseCountryVC()

    let expected = XCTestExpectation(description: "Some Countries to return")


    controller.registerApi(path: "get-country", player_id: 163, contest_id: 1, country_id: 1) { success in if success { expected.fulfill() }
    else{
        XCTFail()
        }
    }

    waitForExpectations(timeout: 1.0) { (_) -> Void in
    }

}

But, whenever I try to test this I get the following error.

[UIApplication applicationState] must be used from main thread only

Once, it also ran well, the test failed, but it ran. But, it is not even running now.

Which line exactly is causing the error? – rmaddy May 29 '18 at 04:55 — rmaddy, May 29 '18 at 04:55

score 3 · Answer 1 · answered May 29 '18 at 04:54

Main Thread Checker detects invalid usage of AppKit, UIKit and other APIs from background threads. completionHandlerseems to update UI so maybe move that part to a separate method and call it from using Dispatch Queue.

DispatchQueue.main.async {
     handleResponseOrError(response, error)
}

ABeard89 · Accepted Answer · 2018-05-29T06:02:43.220

1

(Question changed from being about the main thread to how to define and call closures. This answer has changed to reflect that.)

[UIApplication applicationState] is most likely being called from within the GeneralHelper.

The service helper is most likely making the network request on a background thread.

So, to make sure GeneralHelper is called on the main thread, execute it via a DispatchQueue.

(Also! You're not calling your completion handler, so we'll add that in too.)

func registerApi(path: String, player_id: Int, contest_id: Int, country_id: Int,  completion: ((Bool) -> Void)? = nil)
{
    let helper = ServiceHelper.sharedInstance
    let params = [
        "api_token": Constants.USER_INFO["api_token"].rawValue,
        "player_id": player_id,
        "country_id": country_id,
        "contest_id": contest_id
    ]
    helper.sendRequest(path: "register-country", params: params, showSpinner: true) { (response, error) in
        var success = true

        if let error = error
        {
            // Do stuff on failure.
            success = false
        }
        else
        {
            // Do stuff on success
        }

        // Call completion handler from 'registerApi'
        completion?(success)
    })
}

In your test, you can now add a parameter to test for success.

func testApiWorking()
{
    let controller = WorldCupChooseCountryVC()

    let expected = XCTestExpectation(description: "Some Countries to return")

    controller.registerApi(path: "register-country", player_id: 163, contest_id: 1, country_id: 1) { success in
        if success {
            // Test success
        } else {
            // Test fail
        }

        expected.fulfill()
    }

    waitForExpectations(timeout: 30) { (_) -> Void in
    }
}

edited May 29 '18 at 06:02

answered May 29 '18 at 05:04

ABeard89

911
9
17

In the error and else case I just want to get that if error is not empty it will show in the unit test that something is wrong, else the function is working. – Rob May 29 '18 at 05:18
In that case, I would suggest changing the success handler to accept a boolean parameter indicating success or failure. I'll edit the answer to show this change. – ABeard89 May 29 '18 at 05:20
Added boolean parameter to completion handler. I also changed the name from `success` to `completion` because success or failure is in the parameter. – ABeard89 May 29 '18 at 05:29
I also changed the completion handler to an Optional. This is common practice and makes the method easier to call. – ABeard89 May 29 '18 at 05:30
I am getting this error: Cannot convert value of type '() -> Void' to expected argument type '((Bool) -> Void)?', when in unit test I passed this. controller.registerApi(path: "get-country", player_id: 163, contest_id: 1, country_id: 1) { expected.fulfill() } – Rob May 29 '18 at 05:46
That's because the closure now needs a parameter, just like the closure on `sendRequest` took two: `response` and `error`. Add in a parameter with whatever name you want, and it'll be fine. For example `{ success in }`. – ABeard89 May 29 '18 at 05:49
Then you can test for success in the closure. `{ success in if success { expected.fulfill() } }` – ABeard89 May 29 '18 at 05:50
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/171964/discussion-between-rob-and-abeard89). – Rob May 29 '18 at 06:01

UIApplication applicationState must be used from main thread only

2 Answers2