Unity How to StartCoroutine OnApplicationQuit? - unity3d

Question

I want to fire StartCoroutine(LogOutUser(url, () => { Debug.Log("logOut req done"); }));, which sends data to server ,on OnApplicationQuit function . however it gives this error *
NullReferenceException: Object reference not set to an instance of an object
RegisterLogIn+d__16.MoveNext () (at Assets/Scripts/RegisterLogIn.cs:71)*
RegisterLogIn is class of code below
void LogOut()
{
string url = String.Format("http://localhost:7989/RegisterApi/logout?myTempID={0}", myTempID);
StartCoroutine(LogOutUser(url, () => { Debug.Log("logOut req done"); }));
}
private async void OnApplicationQuit()
{
LogOut();
await websocket.Close();
}
IEnumerator LogOutUser(string url, Action onSuccess)
{
UnityWebRequest req = UnityWebRequest.Get(url);
yield return req.SendWebRequest();
while (!req.isDone)
yield return null;
string result = req.downloadHandler.text;
onSuccess();
}
how can i do this ?

Answer 1

I understand OnApplicationQuit not wait for coroutines because is like another thread and continue with their job.
You can wrapper your own application quit to handle your logout.
public class MyGame : MonoBehaviour
{
public void GameLogic()
{
MyApplication.QuitWithLogOut();
}
}
public class MyApplication : Application
{
public static void QuitWithLogOut()
{
Quiter quiter = new GameObject().AddComponent<Quiter>();
quiter.Quit();
}
}
public class Quiter : MonoBehaviour
{
private bool isLogOutDone;
public void Quit()
{
string url = String.Format("http://localhost:7989/RegisterApi/logout?myTempID={0}", myTempID);
StartCoroutine(LogOutUser(url, () => { Debug.Log("logOut req done"); }));
}
LogOutUser(string url, Action onSuccess)
{
UnityWebRequest req = UnityWebRequest.Get(url);
yield return req.SendWebRequest();
while (!req.isDone)
yield return null;
string result = req.downloadHandler.text;
isLogOutDone = true;
onSuccess();
}
}

Answer 2

If you start a coroutine in OnApplicationQuit.. the application will quit before the coroutine has a chance to finish, and all objects are being destroyed.
According to this thread a simple Get SendWebRequest is threaded with no dependency on the main thread, so it should be safe to block the main thread until complete.
https://forum.unity.com/threads/http-requests-without-coroutines.495418/
You can try blocking the main thread from returning and wait for your network request, but I think you only have a few seconds before unity will hard terminate in that case.
Try this:
void LogOut()
{
string url = String.Format("http://localhost:7989/RegisterApi/logout?myTempID={0}", myTempID);
LogOutUser(url, () => { Debug.Log("logOut req done"); });
}
private async void OnApplicationQuit()
{
LogOut();
await websocket.Close();
}
void LogOutUser(string url, Action onSuccess)
{
UnityWebRequest req = UnityWebRequest.Get(url);
req.SendWebRequest();
while (!req.isDone) {
System.Threading.Thread.Sleep(100);
}
string result = req.downloadHandler.text;
onSuccess();
}