调用此方法时应用程序的状态是什么？

Question

I am implementing push notification in my iOS app.

I am supposed to display some custom View Controller in case the user opens (supposing the app is already running in background) the app from a push notification.

I am implementing this method:

- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler
{
    UIApplicationState state = [[UIApplication sharedApplication] applicationState];

    if (state == UIApplicationStateActive)
    {
        [[NSNotificationCenter defaultCenter] postNotificationName:@"PushNotificationReceived" object:self userInfo:userInfo];
    }
}

I checked the documentation, it says this method gets called whether app is in background or foreground. The system may call it second time when the app is about to enter the foreground, so I am wondering, is the code inside if (state == UIApplicationStateActive) { } going to execute.

Also, there is already some handling of the push notification inside application:didFinishLaunchingWithOptions:, which only gets called at app launch. I guess I should remove it from there as, it may display that View Controller twice.

Please let me know you opinion if you have experience with this issues.

Answer 1

actually I'm not getting your point.

didReceiveRemoteNotification is called ONLY if the app is active and NOT in background . So why do you need to check the state ?

Then, if the app is in background the device receive the push notification, than if the user tap on that, it is opened the app and that method is called .

Otherwise if you open the app without tap on the notification , that method it is not called .

Answer 2

From Apple documentation for the related method:

//This method will be invoked even if the application was launched or resumed because of the remote notification. 
//The respective delegate methods will be invoked first.
- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:(void (^)(UIBackgroundFetchResult result))completionHandler NS_AVAILABLE_IOS(7_0);

Therefore, if you implement the above delegate method, you should NOT handle push notifications in application:didFinishLaunchingWithOptions: because the above method will be called even if application is just launching because of the push notification.

[[UIApplication sharedApplication] applicationState] will have value UIApplicationStateActive only if you application was in foreground at the time push notification is received.

For the case when your application was in background or not running when a push notification is received, there are two scenarios:

1. remote-notification is enabled in UIBackgroundModes. In this case, the above method may be called two times. When the push notification is just received to device, the above method will be called with applicationState having value UIApplicationStateBackground . If user taps to presented push notification, the method will be called again, this time having applicationState value UIApplicationStateInactive .
2. remote-notification is NOT enabled in UIBackgroundModes. In this case, the method will be called only when user tapped to presented push notification.