I tested:
UIControl().sendAction(#selector(URLSessionTask.suspend), to: UIApplication.shared, for: nil)
which is for putting app on background and it works.
How do I put app back on foreground?
I tried:
UIControl().sendAction(#selector(URLSessionTask.resume), to: UIApplication.shared, for: nil)
But eventually it crashes...
Thank you
Update:
Since you've indicated that you're looking for any technical solution, even those not compatible with the App Store or Apple's terms, this should be possible using the Private API LSApplicationWorkspace: openApplicationWithBundleID. Try something like this:
Create a .h file and set up an interface to the LSApplicationWorkspace class and list the required method. You will need to #import "PrivateHeaders.h" in your bridging header.
//
// PrivateHeaders.h
//
#ifndef PrivateHeaders_h
#define PrivateHeaders_h
#interface LSApplicationWorkspace : NSObject
- (bool)openApplicationWithBundleID:(id)arg1;
#end
#endif /* PrivateHeaders_h */
You should then be able to call this function and pass in the Bundle Identifier of your app as an string.
//
// SomeClass.swift
//
import MobileCoreServices
let workspace = LSApplicationWorkspace()
/**
Launch an App given its bundle identifier
- parameter bundleIdentifier: The bundle identifier of the app to launch
- returns: True if app is launched, otherwise false
*/
func openApp(withBundleIdentifier bundleIdentifier: String) -> Bool {
// Call the Private API LSApplicationWorkspace method
return workspace.openApplication(withBundleID: bundleIdentifier)
}
Original:
What you are doing is likely a violation of the iOS Human Interface Guidelines (although the "Don’t Quit Programmatically" is no longer specifically defined), so as the comments have said, it is not suited to the App Store. Regardless, once your app is suspended in this way, I don't expect that there is a way to resume it programmatically, unless you can hook into a Background Operation to run URLSessionTask.resume, but I have not tested it and am unsure whether it can work.
Apps can be launched (and hence brought into the foreground) programmatically from another app or today extension by using a Custom URL Scheme, or via a Push Notification. It isn't possible to launch the app from the Background Operation via a URL Scheme, since it is part of the UIKit framework, which must be run in the main thread.
In summary, I think your best option is to try to use a Notification. This just means that the user will need to click on the notification to bring your app back into the foreground.
Closing/opening the app should be done explicitly by the user. Any other way of closing or opening the app is not supported by Apple and will be rejected when uploaded to app store. iOS Human Interface Guideline states:
Don’t Quit Programmatically
Never quit an iOS application
programmatically because people tend to interpret this as a crash.
However, if external circumstances prevent your application from
functioning as intended, you need to tell your users about the
situation and explain what they can do about it. Depending on how
severe the application malfunction is, you have two choices.
*Display
an attractive screen that describes the problem and suggests a
correction. A screen provides feedback that reassures usersthat
there’s nothing wrong with your application. It puts usersin control,
letting them decide whether they want to take corrective action and
continue using your application or press the Home button and open a
different application
*If only some of your application's features are
not working, display either a screen or an alert when people activate
the feature. Display the alert only when people try to accessthe
feature that isn’t functioning
Just as a follow up to Jordan's excellent answer I want to give an explanation for why your code works in the first place and why that alone will get your app rejected, even without any functionality to make it active again and bring it to the foreground.
As maddy pointed out in a comment, you're basically calling a method from UIApplication's private API. This works due to the Objective-C runtime's dynamic linking. You might wonder "But I am using Swift, what does that have to do with Objective-C?" The answer lies in #selector mechanism. A Selector is basically just a symbol that the Objective-C runtime looks up in a table to get a method it invokes (for you). This is why it's technically not correct to say you "call a method" when you do something like myObjectInstance.someMethod(). The correct way to phrase that would be to "send a message" to the object, because that's what is happening in the runtime. The target-action mechanism is build around that. The sendAction(_: Selector?, to: Any?) method does the same thing. So in effect your code does the following:
Get the symbol that corresponds to URLSessionTask's suspend() method.
Tell the shared instance of UIApplication to invoke the method that it has for that symbol.
Now usually that would result in a crash with the typical "unknown selector sent to instance..." error message. But here, by sure coincidence UIApplication also has a method for that instance (or rather, the runtime also has one of its methods listed in its table for that symbol). You kind of "found" a method that is not declared in its public header. You successfully circumvented a compile-time check for this and invoke a method that is part of a private API. This is explicitly forbidden in the Apple Developer Program License Agreement
Besides all that, I would strongly advise against trying to design an app that way in the first place. As maddy pointed out it's also likely considered to violate the HIGs. Even if you're not trying to do anything malicious and properly explain the feature in your app's description, that won't make Apple let it slide (I assume). Personally, as a user, I'd also find it annoying if the app did something the system already has a specific mechanic for in a different manner, at least in terms of app's coming to background and foreground.
I don't think it can be done without user interaction
The option is you can generate a push notification to tell the user to bring the application to foreground
When the operating system delivers push notification and the target application is not running in the foreground, it presents the notification.
If there is a notification alert and the user taps or clicks the action button (or moves the action slider), the application launches and calls a method to pass in the local-notification object or remote-notification payload.
Related
I tested:
UIControl().sendAction(#selector(URLSessionTask.suspend), to: UIApplication.shared, for: nil)
which is for putting app on background and it works.
How do I put app back on foreground?
I tried:
UIControl().sendAction(#selector(URLSessionTask.resume), to: UIApplication.shared, for: nil)
But eventually it crashes...
Thank you
Update:
Since you've indicated that you're looking for any technical solution, even those not compatible with the App Store or Apple's terms, this should be possible using the Private API LSApplicationWorkspace: openApplicationWithBundleID. Try something like this:
Create a .h file and set up an interface to the LSApplicationWorkspace class and list the required method. You will need to #import "PrivateHeaders.h" in your bridging header.
//
// PrivateHeaders.h
//
#ifndef PrivateHeaders_h
#define PrivateHeaders_h
#interface LSApplicationWorkspace : NSObject
- (bool)openApplicationWithBundleID:(id)arg1;
#end
#endif /* PrivateHeaders_h */
You should then be able to call this function and pass in the Bundle Identifier of your app as an string.
//
// SomeClass.swift
//
import MobileCoreServices
let workspace = LSApplicationWorkspace()
/**
Launch an App given its bundle identifier
- parameter bundleIdentifier: The bundle identifier of the app to launch
- returns: True if app is launched, otherwise false
*/
func openApp(withBundleIdentifier bundleIdentifier: String) -> Bool {
// Call the Private API LSApplicationWorkspace method
return workspace.openApplication(withBundleID: bundleIdentifier)
}
Original:
What you are doing is likely a violation of the iOS Human Interface Guidelines (although the "Don’t Quit Programmatically" is no longer specifically defined), so as the comments have said, it is not suited to the App Store. Regardless, once your app is suspended in this way, I don't expect that there is a way to resume it programmatically, unless you can hook into a Background Operation to run URLSessionTask.resume, but I have not tested it and am unsure whether it can work.
Apps can be launched (and hence brought into the foreground) programmatically from another app or today extension by using a Custom URL Scheme, or via a Push Notification. It isn't possible to launch the app from the Background Operation via a URL Scheme, since it is part of the UIKit framework, which must be run in the main thread.
In summary, I think your best option is to try to use a Notification. This just means that the user will need to click on the notification to bring your app back into the foreground.
Closing/opening the app should be done explicitly by the user. Any other way of closing or opening the app is not supported by Apple and will be rejected when uploaded to app store. iOS Human Interface Guideline states:
Don’t Quit Programmatically
Never quit an iOS application
programmatically because people tend to interpret this as a crash.
However, if external circumstances prevent your application from
functioning as intended, you need to tell your users about the
situation and explain what they can do about it. Depending on how
severe the application malfunction is, you have two choices.
*Display
an attractive screen that describes the problem and suggests a
correction. A screen provides feedback that reassures usersthat
there’s nothing wrong with your application. It puts usersin control,
letting them decide whether they want to take corrective action and
continue using your application or press the Home button and open a
different application
*If only some of your application's features are
not working, display either a screen or an alert when people activate
the feature. Display the alert only when people try to accessthe
feature that isn’t functioning
Just as a follow up to Jordan's excellent answer I want to give an explanation for why your code works in the first place and why that alone will get your app rejected, even without any functionality to make it active again and bring it to the foreground.
As maddy pointed out in a comment, you're basically calling a method from UIApplication's private API. This works due to the Objective-C runtime's dynamic linking. You might wonder "But I am using Swift, what does that have to do with Objective-C?" The answer lies in #selector mechanism. A Selector is basically just a symbol that the Objective-C runtime looks up in a table to get a method it invokes (for you). This is why it's technically not correct to say you "call a method" when you do something like myObjectInstance.someMethod(). The correct way to phrase that would be to "send a message" to the object, because that's what is happening in the runtime. The target-action mechanism is build around that. The sendAction(_: Selector?, to: Any?) method does the same thing. So in effect your code does the following:
Get the symbol that corresponds to URLSessionTask's suspend() method.
Tell the shared instance of UIApplication to invoke the method that it has for that symbol.
Now usually that would result in a crash with the typical "unknown selector sent to instance..." error message. But here, by sure coincidence UIApplication also has a method for that instance (or rather, the runtime also has one of its methods listed in its table for that symbol). You kind of "found" a method that is not declared in its public header. You successfully circumvented a compile-time check for this and invoke a method that is part of a private API. This is explicitly forbidden in the Apple Developer Program License Agreement
Besides all that, I would strongly advise against trying to design an app that way in the first place. As maddy pointed out it's also likely considered to violate the HIGs. Even if you're not trying to do anything malicious and properly explain the feature in your app's description, that won't make Apple let it slide (I assume). Personally, as a user, I'd also find it annoying if the app did something the system already has a specific mechanic for in a different manner, at least in terms of app's coming to background and foreground.
I don't think it can be done without user interaction
The option is you can generate a push notification to tell the user to bring the application to foreground
When the operating system delivers push notification and the target application is not running in the foreground, it presents the notification.
If there is a notification alert and the user taps or clicks the action button (or moves the action slider), the application launches and calls a method to pass in the local-notification object or remote-notification payload.
I have been working on iOS framework (in Swift) which contains beacon functionality. I made it work except that I'm not sure how to handle scenario where I'm in foreground and I encounter multiple beacons in short duration.
If I want didReceive delegate method to show Alert for beacon while in foreground, and if I encounter many beacons it will not work nicely (alerts will display one over another). Is there some solution to queue notifications somehow?
Also I would like to know, if there is a way to make all that logic for receiving local notifications inside my framework?
I have to be able to support iOS-8.0 so I can't use Notification Center which is available from iOS-10.0
Can I create some class which would act like appdelegate (probably some class which would implement UIApplicationDelegate inside framework), is something like that possible?
I want to put as much code as I can inside framework itself so that it won't be too messy job for someone to include that framework with all functionality.
After some time I figured out a way to make this. I'm beginner in iOS with few months experience so I can't say if this solution is the best but it works for me.
I found a way to implement all push and local notification related delegate methods from framework. Basically if main application wants framework to take care of notifications without having to implement anything yourself, on runtime framework will dynamically implement certain UIApplicationDelegate methods for AppDelegate.swift class (or whatever is your AppDelegate class called).
I used object_getClass(UIApplication.shared.delegate!) to get the main class.
Then I used func class_addMethod(_ cls: AnyClass!, _ name: Selector!, _ imp: IMP!, _ types: UnsafePointer!) -> Bool
to implement delegate methods for push and local notifications from inside framework so now it comes down to write one or two lines to use framework entirely with working notifications and beacon location services instead of having to write a lots of code outside framework.
As for handling notifications in foreground mode I made that work by adding them to queue so that if more than one notification comes, and wants to be displayed in foreground regime, only one will be displayed by UIAlertController and the rest will be put in queue and sent again but with some small delay (I set fire date to be some value which I thought was appropriate in my case) after user makes an action regarding that first notification which was the only one presented.
These are just my ideas for the problems I had, if someone shows interest for these solutions I will write more details if needed. I will also gladly accept any criticism.
At some point in my application I have done this exit(0) which crashes my app. But I haven't figured out what method gets called when this executes.
I've put messages in:
(void)applicationWillTerminate:(UIApplication *)application
(void)applicationDidEnterBackground:(UIApplication *)application
But none of this seem to get called! Any idea about what method is called when exit(0) is done?
From Apple's Human User Guidelines...
Don’t Quit Programmatically
Never quit an iOS application programmatically because people tend to
interpret this as a crash. However, if external circumstances prevent
your application from functioning as intended, you need to tell your
users about the situation and explain what they can do about it.
Depending on how severe the application malfunction is, you have two
choices.
Display an attractive screen that describes the problem and suggests a
correction. A screen provides feedback that reassures users that
there’s nothing wrong with your application. It puts users in control,
letting them decide whether they want to take corrective action and
continue using your application or press the Home button and open a
different application
If only some of your application's features are not working, display
either a screen or an alert when people activate the feature. Display
the alert only when people try to access the feature that isn’t
functioning.
If you've decided that you are going to quit programmatically anyway...
In C, exit(0) will halt execution of the application. This means that no delegate methods or exception handlers will be called. So, if the goal is to make sure that some code gets called when the closes, even on a forced close, there may be another option. In your AppDelegate implement a custom method called something like -(void)applicaitonIsgoingAway. Call this method from within anywhere you want your exiting code to be called:
applicationWillTerminate
applicationDidEnterBackground
onUncaughtException
The first two are ones that you already mentioned in your question. The third can be a catch-all of sorts. It's a global exception handler. This next bit comes from a question on that very topic.
This exception handler will get called for any unhanded exceptions (which would otherwise crash your app). From within this handler, you can call applicaitonIsgoingAway, just like in the other 2 cases. From the other question that I mentioned above, you can find an answer similar to this.
void onUncaughtException(NSException* exception)
{
[[AppDelegate sharedInstance] applicationIsgoingAway];
}
But in order for this to work, you need to set this method up as the exception handler like so...
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
NSSetUncaughtExceptionHandler(&onUncaughtException);
//There may already be more code in this method.
}
Now, you can quit the app programmatically by calling NSAssert(FALSE, #"Quitting the app programmatically."); As long as there is no other exception handler in place to catch this, your app will begin to crash, and your exception handler code will be called. in-turn calling applicationIsGoingAway.
When you call exit(0) you immediately terminate your application. 0 is a status code which means successful termination.
No other method is called, you application just dies. As a result end user may think app is just crashed.
Apple discourages you to call exit anywhere.
exit(0) is a C function that terminates your app's process therefore none of the application delegates methods will be called, the app will be killed immediately. Apple recommends strongly against your app quitting because it appears broken to the user.
There is no Apple-supported method to terminate your application programmatically. Calling exit is certainly out of the question. This causes all sorts of bugs (for example the multitasking switcher will break badly) as well as simply being wrong.
If you are trying to disable multitasking, you can do this with the UIApplicationExitsOnSuspend key in your Info.plist file (the title for the key is "Application does not run in background").
Other than that, it's up to your users to press the home button to close your application.
these methods will be called but you cannot use exit(0) you will need to press the back button to close your app then these methods will be called
So, I have an app that monitors significant location changes. I want to only record changes at most every 2 hours. The other times, I really don't want my app to startup at all. Does anyone know if I can terminate my app from within
- (BOOL) application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
Will returning "False" cause my app not to be loaded (from the docs it seems that is only if it is trying to handle a URL).
You should not terminate the app as it lead to rejection by apple.As docs say
There is no API provided for gracefully terminating an iOS application.
You can show pop up to user for appropriate message.During development or testing you can call abort().But you should not ship your app with any of terminate api as apple strongly discourage this.
you can try exit(0); but Let me warn you apple may reject your app if you terminate your app willingly, what would be better is to show a dialogue box containing the reason and asking the user to close the app on thier own.
You really should not terminate your application, but should prompt the user that there's nothing to show at the moment and have them go to the home screen.
However, if you really want to, you can use abort().
From Apple's Developer Library (emphasis added):
In iOS, the user presses the Home button to close applications. Should your application have conditions in which it cannot provide its intended function, the recommended approach is to display an alert for the user that indicates the nature of the problem and possible actions the user could take — turning on WiFi, enabling Location Services, etc. Allow the user to terminate the application at their own discretion.
[...]
If during development or testing it is necessary to terminate your application, the abort function, or assert macro is recommended.
I want to exit my application programatically, I googled, some people suggesting to use exit(1), but apple is not supporting that I guess. If it is the case, How do I exit my application programatically. Any helps appreciated.
exit(0); will work but don't use it
You shouldn't force close an app as the standard way to terminate an application is to press the home button (or use the multitasking bar)
Don’t Quit Programmatically
Never quit an iOS application programmatically because people tend to
interpret this as a crash. However, if external circumstances prevent
your application from functioning as intended, you need to tell your
users about the situation and explain what they can do about it.
Depending on how severe the application malfunction is, you have two
choices.
Display an attractive screen that describes the problem and suggests a
correction. A screen provides feedback that reassures users that
there’s nothing wrong with your application. It puts users in control,
letting them decide whether they want to take corrective action and
continue using your application or press the Home button and open a
different application
If only some of your application's features are not working, display
either a screen or an alert when people activate the feature. Display
the alert only when people try to access the feature that isn’t
functioning.
Source
I believe u are not reading the comment properly thus posting the answer for ur question here:
"Simply Don't do that. as apple does not allow application to crash like that."
look at here. How do I exit my iOS app gracefully after handling a Local Notification and here Exit application in iOS 4.0 there are fare discussion over here.
After the release of iOS4, multitasking(new feature) was added by APPLE. This feature enabled the users to keep the app into suspended state in the background if in between he has to do some other activity(e.g. picking up phone call). So Apple considers your app should be maintained in the background until the user deletes the application from the background. And after this if you want to exit use exit(0);, using this would further lead to rejection from AppStore
Here's a wrong way to accomplished exit function in your app. This is coming to mind when I read your question, never applied anywhere, so be careful if you'll gonna implement this!
- (void) exitApp
{
NSArray *array = [[[NSArray alloc] init] autorelease];
NSLog(#"%#",[array objectAtIndex:10]); //will crash here, looks like exit.
}
P.S. You can put this code inside your UIAlertView asking exit confirmation like Do you really want to exit?. In YES button pressed you can call [self exitApp]; User think that he'll exit from the app.