I've created an app that has two viewcontrollers. The app opens to a title screen (general UIViewController titled 'Title') with a segue connection to the second view that is a custom class (OSViewController titled 'MapView'). As it is, the app suspends when entered into the background state so it opens right where you left off which is typically in MapView.
I want to know what I need to do to have the app start at the title screen when it becomes active. Preferably, I'd like it to open to the title screen if it is inactive for more than 1 minute. From what I've been reading, it seems like I would make a call in applicationDidBecomeActive: method in my AppDelegate to code this in. Please provide me the code to put in the applicationDidBecomeActive: method (if that's the right place to put it) that will reopen my app to the title screen when transitioning from the inactive state to the active state. My app is almost finished but I'd like to fix this issue and I don't have a lot of experience dealing with app states. Thanks in advance for your time.
If you need more information just ask.
You can also register a class as an observer of the "didBecomeActive" notification. You should place this in the viewDidLoad or the init method of your class.
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(willBecomeActive:) name:UIApplicationDidBecomeActiveNotification object:nil];
In this case, willBecomeActive: is a method that you have defined in your class that get's called when the app becomes active again. That might look something like this:
- (void)willBecomeActive:(NSNotification *)notification {
if (self.navigationController.topViewController == self) {
[self.navigationController popToRootViewControllerAnimated:YES];
}
}
You'll also need to add this in your viewDidUnload method
[[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationDidBecomeActiveNotification object:nil];
EDIT:
Thanks #AMayes for the advice. I don't believe key/value observing is necessary in this instance.
Related
I'm using storyboard.
As I remeber (I worked with ios 4, long time ago=)) everytime, when View appears, calls
-(void)viewWillAppear:(BOOL)Animated {}
method.
Now this method doesn't call, if I press Home button and run app again.
How to fix it?
I need to update one UIView if it appears after home pressing.
The function viewWillAppear is not part of UIView. It is part of UIViewController.
It is called after the view controller's view has been loaded and just before it starts to transition onto screen.
If you create a subclass of UIView and put this function in it then it will never be called because it isn't supposed to be.
Edit
You are correct that viewWillAppear does not get called when the app is coming back from the background.
If you want to update a part of your app when this happens then you can do something in the AppDelegate.
I'd recommend not trying to store properties etc... in the AppDelegate though. You should do something like this...
- (void)applicationWillEnterForeground:(UIApplication *)application
{
// Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
// just pass the message on. In your view you will need to add an observer for this notification
[[NSNotificationCenter defaultCenter] postNotificationName:#"UpdateViewNotification" object:nil];
}
try this, call the super,
-(void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
}
When my application is interrupted, such as receiving a phone call, screen locked, or switching applications, I need it to respond differently depending on which view/viewcontroller is on screen at the time of the interruption.
in my first view controller, we'll call it VCA, I have this
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:#selector(doSomething)
name:UIApplicationWillResignActiveNotification
object:NULL];
-(void)doSomething{
//code here
};
In VCB I have
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:#selector(doSomethingElse)
name:UIApplicationWillResignActiveNotification
object:NULL];
-(void)doSomethingElse{ //code here };
but if VCB is on screen, or any subsequent view controller (vcc, vcd, vce), and the screen is locked, it will only respond to the doSomething method defined in VCA. Even if I don't have the UIApplicationWillResignActiveNotification in one of the view controllers that comes after VCA, it will still respond to the doSomethign method defined in VCA.
Is there any way I can make my application respond differently depending on which view is on screen when it goes into the background?
This works for me in applicationDidEnterBackground
if ([navigationViewController.visibleViewController isKindOfClass:[YourClass class]]) {
//your code
}
Are you saying your doSomethingElse function is never called? Are you sure of this, maybe it is getting called in addition to doSomething? I think so.
In which case in doSomething and doSomethingElse you could add a check as the first line to ignore the notification if not currently loaded:
if ([self isLoaded] == NO)
return;
How about you check the current visibleViewController when you received the notification? If it matches with your receiver than perform the action(s), otherwise ignore it.
I have a Single View Application. When I hit the home button and ‘minimise’ the application I want to be able to execute code when the user reopens it.
For some reason viewDidAppear and viewWillAppear do not execute when I minimise and reopen the application.
Any suggestions?
Thanks in advance
sAdam
You can either execute code in the app delegate in
- (void)applicationDidBecomeActive:(UIApplication *)application
or register to observe the UIApplicationDidBecomeActiveNotification notification and execute your code in response.
There is also the notification UIApplicationWillEnterForegroundNotification and the method - (void)applicationWillEnterForeground:(UIApplication *)application in the app delegate.
To hook up notifications add this at an appropriate point
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(didBecomeActive:)
name:UIApplicationDidBecomeActiveNotification
object:nil];
Define a the corresponding method
- (void)didBecomeActive:(NSNotification *)notification;
{
// Do some stuff
}
Then don't forget to remove yourself an observer at an appropriate point
[[NSNotificationCenter defaultCenter] removeObserver:self];
Discussion
You most likely only want your viewController to respond to events whilst it is the currently active view controller so a good place to register for the notifications would be viewDidLoad and then a good place to remove yourself as an observer would be viewDidUnload
If you are wanting to run the same logic that occurs in your viewDidAppear: method then abstract it into another method and have viewDidAppear: and the method that responds to the notification call this new method.
This is because since Apple implemented "Multitasking", apps are completely reloaded when you start them again, just as if you had never closed them. Because of this, there is no reason for viewDidAppear to be called.
You could either implement
- (void)applicationWillEnterForeground:(UIApplication *)application
and do there what ever you want. Or you register for the notification UIApplicationWillEnterForegroundNotification in your view controller. Do this in viewDidLoad:
[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(myAppWillEnterForeground)
name:UIApplicationWillEnterForegroundNotification object:nil];
And of course implement the specified selector and do there what you want.
I am not sure how the answer by #Paul.s performs the OP request since registering UIApplicationDidBecomeActiveNotification will be executed twice:
When launching the app
When application goes into the background
A better practice will be to decouple those events into 2 different notifications:
UIApplicationDidBecomeActiveNotification:
Posted when the app becomes active.
An app is active when it is receiving events. An active app can be said to have focus. It gains focus after being launched, loses focus when an overlay window pops up or when the device is locked, and gains focus when the device is unlocked.
Which basically means that all logic related to "when application launched for the first time"
UIApplicationWillEnterForegroundNotification:
Posted shortly before an app leaves the background state on its way to becoming the active app.
Conclusion
This way we can create a design that will perform both algorithms but as a decoupled way:
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(yourMethodName1) name:UIApplicationWillEnterForegroundNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(yourMethodName2) name:UIApplicationDidBecomeActiveNotification object:nil];
This because you don't redraw your view. Use applicationWillEnterForeground in the AppDelegate instead. This should work fine for you.
What is the best way to display a view (in my case a login screen) on app resume. From looking around, I've been playing with the applicationDidBecomeActive event in my AppDelegate, but I cannot seem to get my head around how to properly display a view from here.
I've tried to grab the current window by using self.window and/or it's subviews, but from the AppDelegate self.window is nil.
So far this application seems to be wired up correctly, but I am baffled by two things.
A) why is self.window nil from within my AppDelegate's applicationDidBecomeActive event handler.
B) what is the correct/normal way of display a login view (or the like) on application resume.
Implement a custom UIViewController for all of your applications to inherent from. In this view controller implement logic in the viewWillAppear message to determine and show the login screen if necessary.
//CustomViewController.h
#interface CustomViewController : UIViewController
#end
//CustomerViewController.m
#implementation CustomViewController
-(void)viewWillAppear:(BOOL)animated{
if(login_required){
LoginViewController *loginView = [[LoginViewController alloc] initWithNibName:#"LoginView" bundle:nil];
[self presentModalViewController:loginView animated:false];
}
}
#end
Then, simply, in your login view controller make sure you call:
[self dismissModalViewControllerAnimated:false];
The benefits of this approach are two fold. Firstly, it's a very simple implementation. However, most compellingly, having a base class for an application's view controller presents the opportunity to extract common logic.
Jason,
I have worked on a security tutorial provided by Chris Lowe on raywenderlich.com that was intended to demonstrate how to use basic iOS security to lock the application.
The premise behind this tutorial though was that the application would prompt for login upon first launch and if application was resumed upon unlocking the device through the use of NSNoftificationCenter in viewDidLoad and subscribe the the notifications: deviceWillLock and deviceWillUnlock. All of this assumes the device is set to lock.
Basic iOS Security Tutorial Part 2 - This is the part that has the NSNotification registration.
Basic iOS Security Tutorial Part 1 - This is the first part of the tutorial for clarity.
I also ran into this problem and came across this question whilst researching a solution. I didn't want to create the intermediate super class for my views and I wasn't sure how it would work out with navigation controllers. I have come up with another solution that works well for me - so thought I would share it. It is based around the use of NSNotificationCenter .
In your app delegate create a property to hold a reference to the currently displayed view controller - say currentViewController.
Then in the applicationDidFinishLaunching method, register a block observer to update the currentViewController property like this:
[[NSNotificationCenter defaultCenter] addObserverForName:#"CurrentViewChanged"
object:nil
queue:nil
usingBlock:^(NSNotification *note)
{self.currentViewController = (UIViewController *)note.object;} ];
In your view controller implementations, update the viewDidAppear methods to notify the observer that a new view controller is being displayed by adding the following line
[[NSNotificationCenter defaultCenter] postNotificationName:#"CurrentViewChanged" object:self];
Finally, include code in the applicationDidBecomeActive method in your app delegate to force the modal display of your login screen.
UIStoryboard *mainStoryBoard = self.window.rootViewController.storyboard;
UnlockViewController *uvc = [mainStoryBoard instantiateViewControllerWithIdentifier:#"modalUnlockView"];
uvc.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
[self.currentViewController presentViewController:uvc animated:YES completion:NULL];
A couple of additional items to note :-
You can disable the login screen display at anytime by posting a notification where the view controller passed is nil.
You only need to post the notification once for a navigation view controller at the top level. All view controllers in the navigation controller stack will be covered. I haven't checked, but I suspect the same is true for a tab view controller.
If you want to display the login screen the first time you enter the app after startup then include the following line in the applicationDidFinishLaunching method.
self.currentViewController = self.window.rootViewController;
I hope this is of some use.
Thanks
I am making a game for iPhone and want to be able to pause a timer when a user's game is interrupted like when they hit the home button. I know that in the app delegate there is a method when the app leaves the foreground called:
- (void)applicationWillResignActive:(UIApplication *)application
What I am struggling with is how to pause the timer. I have a function in my view controller that's called pauseGame and is used for when the user wants to pause the game. I was thinking that it would be easiest to pause the game by using this method. I cannot however understand how to call this method. Any ideas? And sorry for the beginner question.
The shortest way is to Use Notifications:
1. define a custom notification, at your application delegate (or anywhere else...)
#define kApplicationWillResignActiveNotification
#"kApplicationWillResignActiveNotification"
2. dispatch the notification when the applicationWillResignActive: method is called
[[NSNotificationCenter defaultCenter] postNotificationName:
kApplicationWillResignActive object:nil];
3. listen to that notification where ever you want in your project (* import the header file where you #defined the notification)
[[NSNotificationCenter defaultCenter] addObserver:self
selector: #selector(appResigned:)
name:kApplicationWillResignActiveNotification object: nil];
4. you can get the NSNotification Object if you add it to your selector
-(void)appResigned:(NSNotification *)notification;