When you close the application, boolean not set to no - ios

Question

I use Firebase in the application. I want to record the user's status in the database, it is currently in the application or not. I use the code from the official document, which must ensure this task. When the application is opened, the value is set to NO, and then changed to YES. But at the close of the application as well as the transition to the background, the block is not called and the value does not change. Here is my code...
FIRDatabaseReference *connectedRef = [[FIRDatabase database] referenceWithPath:#".info/connected"];
[connectedRef observeEventType:FIRDataEventTypeValue withBlock:^(FIRDataSnapshot * _Nonnull snapshot) {
if([snapshot.value boolValue]) {
NSLog(#"CONNECTED");
} else {
NSLog(#"NOT CONNECTED");
}
}];
2017-01-17 13:36:38.203 Tricker[6293:817528] NOT CONNECTED
2017-01-17 13:36:40.863 Tricker[6293:817528] CONNECTED
The console comes the following information, which shows that the value changes after two seconds after the opening of the application with NO to YES. But nothing happens when the application is closed...
Prompt in what could be the problem?

Answer 1

You seem to be confusing connection state and application lifecycle.
When it is active, the Firebase Database client will fire information about its connection state on the .info/connected path.
But when the app is not active, the client has no way of firing this information anymore. You will need to use regular iOS application lifecycle events to detect when the app becomes inactive.
Recording the user's presence in the database works as a two-step process:
when the application starts you write a value to the database to signal that the user is online
when the application starts, you tell the database server to write another value to the database that signals that the user is gone.
Step 2 is accomplished by onDisconnectSetValue:
[presenceRef onDisconnectSetValue:#"I disconnected!"];
The trick is that you call this method early on, typically when your app starts. The write operation will be executed when the Firebase Database server detects that the client disconnected.
This disconnect can happen in two ways:
when the client closes the connection explicitly
when the the socket that the server uses to communicate with the client times out
When your app crashes, you're in situation 2. In that case it can take a few minutes before the server detects that the client is gone, since you're waiting for a socket to time-out.

Answer 2

You close the app means ? two things possibility
User can put app in Background :
Here you can set a NSUSEDefault value like :
(void)applicationDidEnterBackground:(UIApplication *)application {
[[NSUserDefaults standardUserDefaults] setBool:NO
forKey:#"YOUR_KEY"]; [[NSUserDefaults standardUserDefaults]
synchronize];
}
User can remove app from background :
(void)applicationWillTerminate:(UIApplication *)application {
[[NSUserDefaults standardUserDefaults] setBool:NO forKey:#"YOUR_KEY"];
[[NSUserDefaults standardUserDefaults] synchronize];
}