Show an alert when iOS app is in the background

问题:

I want to show an alert view when my iOS app is in the background (and it's using location).

For example, the Uber Partner (Driver) app shows an alert and plays a sound even when:

• I have turned off notifications!
• My iPhone is in Silent mode!

I am aware of the local notifications approach and it doesn't work if the user turns off/ changes the Notifications in Settings. I am looking for something different.

Actions performed to reach the above state:

• Go online on Uber Partner App (you are the driver!)
• Disable Notifications for the app in Settings
• Move the app to background and wait for a Ride Request
• After some time, a ride Request is popped up as an Alert view and a sound is played in the background

Of course, silent remote notifications can be tapped in by the app using the didReceiveRemoteNotification: fetchCompletionHandler: API even if the user disables Notifications in Settings. But, how the alert is popped up, that's what I am trying to find out.

回答1:

I would imagine that Uber has some special permissions or uses some private API that allow them to achieve this behavior without using local notifications. While I don't know how Uber implemented this in their partner app, I can talk a little bit about how alerts work on the home screen.

SpringBoard is the singleton class that manages the SpringBoard application (SpringBoard.app), the application launcher for the iPhone. SpringBoard doesn't use the standard UIAlertView/UIAlertController classes, since they don't participate in the SpringBoard-wide alert system. iOS 5 introduced SBAlertItem the which is used to display UIAlertViews on SpringBoard (Battery Notification Alerts, Sim Unlock Alert, etc.). Apple uses SBAlertItem for their lock and home screen alerts, I'll be working on the assumption that Uber is using an SBAlertItem for this answer.

SBAlertItem has a protected ivar UIAlertView *_alertSheet. Assuming this acts as a normal UIAlertView, you should be able to change the properties on this alert to fit your needs. I would also read through saurik's Cydia Substrate project, specifically MobileSafety.mm to see some use cases. I've also found noweibogoodsleep which provides an example of using SBAlertItem on the SpringBoard.

I've also found SBUserNotificationAlert, a subclass of SBAlertItem. This appears to have more methods to facilitate alert customization that may fit your needs better than the standard SBAlertItem.

I realize hooking into private APIs is probably not what you were expecting when asking this question. Since I don't know how Uber works, I can only provide an answer from my personal experience working with the runtime and jailbroken devices.

回答2:

After some static analysis of the binary, it became clear that they are not using PKPushRegistry (VOIP), undocumented NSNotificationCenter calls or SBAlertItem.

Took a little while to find it, but they are actually using CFUserNotification for the alerts. The class is documented for Mac, but private for iOS.

I found the usage by doing this:

nm -u ~/Downloads/Payload/UberDriver.app/UberDriver | grep CFUserNotification

The output is:

_CFUserNotificationCancel
_CFUserNotificationCreate
_CFUserNotificationCreateRunLoopSource
_kCFUserNotificationAlertHeaderKey
_kCFUserNotificationAlertMessageKey
_kCFUserNotificationAlertTopMostKey
_kCFUserNotificationAlternateButtonTitleKey
_kCFUserNotificationDefaultButtonTitleKey
_kCFUserNotificationSoundURLKey

If I grep for PKPushRegistry or for SBAlertItem, both return no results.

Can use the class by importing this file to your project.

UPDATE

I have 'working' code, however it immediately calls the callback function (responseFlags set to kCFUserNotificationCancelResponse) without showing the alert..

I am using the same keys and calls as the Uber app (compare code below to list above), so there must be something extra. Will keep looking.

#import "CFUserNotification.h"

@interface AppDelegate ()
@property (nonatomic) CFRunLoopSourceRef runLoopSource;
@property (nonatomic) CFUserNotificationRef notification;
@end

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    SInt32 error;
    NSDictionary *keys = @{(__bridge NSString*)kCFUserNotificationAlertHeaderKey: @"Hello",
                           (__bridge NSString*)kCFUserNotificationAlertMessageKey: @"World",
                           (__bridge NSString*)kCFUserNotificationAlertTopMostKey: @YES,
                           (__bridge NSString*)kCFUserNotificationDefaultButtonTitleKey: @"asdf",
                           (__bridge NSString*)kCFUserNotificationAlternateButtonTitleKey: @"asdf",
                           };

    self.notification = CFUserNotificationCreate(NULL, 10, kCFUserNotificationPlainAlertLevel, &error, (__bridge CFDictionaryRef)keys);
    self.runLoopSource = CFUserNotificationCreateRunLoopSource(NULL, self.notification, NotificationCallback, 0);
    CFRunLoopAddSource(CFRunLoopGetMain(), self.runLoopSource, kCFRunLoopCommonModes);

    return YES;
}

void NotificationCallback(CFUserNotificationRef userNotification, CFOptionFlags responseFlags) {
    NSLog(@"got response: %lu", responseFlags);
}

回答3:

Your question missed the most important part regarding the "Uber Partner" app that would make things a lot clearer. The "Uber Partner" app is an Enterprise app and is not restricted to the Appstore guide lines.

it didn't got any special permissions like other answers suggested.

It is possible to display an alert view using SBAlertItem regardless of Sound \ Notification settings but if your end goal is to make it to the appstore, unfortunately, your app will be rejected for using private API.