Implement app lifecycle reactivity.

GoogleDataTransport.podspec

@@ -41,6 +41,11 @@ Shared library for iOS SDK data transport needs.
     test_spec.source_files = ['GoogleDataTransport/Tests/Unit/**/*.{h,m}'] + common_test_sources
   end
 
+  s.test_spec 'Tests-Lifecycle' do |test_spec|
+    test_spec.requires_app_host = false
+    test_spec.source_files = ['GoogleDataTransport/Tests/Lifecycle/**/*.{h,m}'] + common_test_sources
+  end
+
   # Integration test specs
   s.test_spec 'Tests-Integration' do |test_spec|
     test_spec.requires_app_host = false

GoogleDataTransport/GoogleDataTransport/Classes/GDTLifecycle.m

@@ -69,27 +69,27 @@ - (void)dealloc {
 }
 
 - (void)applicationDidEnterBackground:(NSNotification *)notification {
-  //  UIApplication *application = [UIApplication sharedApplication];
-  //  [[GDTTransformer sharedInstance] appWillBackground:application];
-  //  [[GDTStorage sharedInstance] appWillBackground:application];
-  //  [[GDTUploadCoordinator sharedInstance] appWillBackground:application];
-  //  [[GDTRegistrar sharedInstance] appWillBackground:application];
+  UIApplication *application = [UIApplication sharedApplication];
+  [[GDTTransformer sharedInstance] appWillBackground:application];
+  [[GDTStorage sharedInstance] appWillBackground:application];
+  [[GDTUploadCoordinator sharedInstance] appWillBackground:application];
+  [[GDTRegistrar sharedInstance] appWillBackground:application];
 }
 
 - (void)applicationWillEnterForeground:(NSNotification *)notification {
-  //  UIApplication *application = [UIApplication sharedApplication];
-  //  [[GDTTransformer sharedInstance] appWillForeground:application];
-  //  [[GDTStorage sharedInstance] appWillForeground:application];
-  //  [[GDTUploadCoordinator sharedInstance] appWillForeground:application];
-  //  [[GDTRegistrar sharedInstance] appWillForeground:application];
+  UIApplication *application = [UIApplication sharedApplication];
+  [[GDTTransformer sharedInstance] appWillForeground:application];
+  [[GDTStorage sharedInstance] appWillForeground:application];
+  [[GDTUploadCoordinator sharedInstance] appWillForeground:application];
+  [[GDTRegistrar sharedInstance] appWillForeground:application];
 }
 
 - (void)applicationWillTerminate:(NSNotification *)notification {
-  //  UIApplication *application = [UIApplication sharedApplication];
-  //  [[GDTTransformer sharedInstance] appWillTerminate:application];
-  //  [[GDTStorage sharedInstance] appWillTerminate:application];
-  //  [[GDTUploadCoordinator sharedInstance] appWillTerminate:application];
-  //  [[GDTRegistrar sharedInstance] appWillTerminate:application];
+  UIApplication *application = [UIApplication sharedApplication];
+  [[GDTTransformer sharedInstance] appWillTerminate:application];
+  [[GDTStorage sharedInstance] appWillTerminate:application];
+  [[GDTUploadCoordinator sharedInstance] appWillTerminate:application];
+  [[GDTRegistrar sharedInstance] appWillTerminate:application];
 }
 
 @end

GoogleDataTransport/GoogleDataTransport/Classes/GDTRegistrar.m

@@ -89,4 +89,39 @@ - (void)registerPrioritizer:(id<GDTPrioritizer>)prioritizer target:(GDTTarget)ta
   return targetToPrioritizer;
 }
 
+#pragma mark - GDTLifecycleProtocol
+
+- (void)appWillBackground:(nonnull UIApplication *)app {
+  dispatch_async(_registrarQueue, ^{
+    for (id<GDTUploader> uploader in [self->_targetToUploader allValues]) {
+      [uploader appWillBackground:app];
+    }
+    for (id<GDTPrioritizer> prioritizer in [self->_targetToPrioritizer allValues]) {
+      [prioritizer appWillBackground:app];
+    }
+  });
+}
+
+- (void)appWillForeground:(nonnull UIApplication *)app {
+  dispatch_async(_registrarQueue, ^{
+    for (id<GDTUploader> uploader in [self->_targetToUploader allValues]) {
+      [uploader appWillForeground:app];
+    }
+    for (id<GDTPrioritizer> prioritizer in [self->_targetToPrioritizer allValues]) {
+      [prioritizer appWillForeground:app];
+    }
+  });
+}
+
+- (void)appWillTerminate:(nonnull UIApplication *)app {
+  dispatch_sync(_registrarQueue, ^{
+    for (id<GDTUploader> uploader in [self->_targetToUploader allValues]) {
+      [uploader appWillTerminate:app];
+    }
+    for (id<GDTPrioritizer> prioritizer in [self->_targetToPrioritizer allValues]) {
+      [prioritizer appWillTerminate:app];
+    }
+  });
+}
+
 @end

GoogleDataTransport/GoogleDataTransport/Classes/GDTStorage.h

@@ -16,13 +16,15 @@
 
 #import <Foundation/Foundation.h>
 
+#import <GoogleDataTransport/GDTLifecycle.h>
+
 @class GDTEvent;
 @class GDTStoredEvent;
 
 NS_ASSUME_NONNULL_BEGIN
 
 /** Manages the storage of events. This class is thread-safe. */
-@interface GDTStorage : NSObject <NSSecureCoding>
+@interface GDTStorage : NSObject <NSSecureCoding, GDTLifecycleProtocol>
 
 /** Creates and/or returns the storage singleton.
  *

GoogleDataTransport/GoogleDataTransport/Classes/GDTStorage.m

@@ -23,6 +23,7 @@
 #import "GDTAssert.h"
 #import "GDTConsoleLogger.h"
 #import "GDTEvent_Private.h"
+#import "GDTLifecycle.h"
 #import "GDTRegistrar_Private.h"
 #import "GDTUploadCoordinator.h"
 
@@ -75,6 +76,13 @@ - (instancetype)init {
 - (void)storeEvent:(GDTEvent *)event {
   [self createEventDirectoryIfNotExists];
 
+  __block UIBackgroundTaskIdentifier bgID = UIBackgroundTaskInvalid;
+  if (_runningInBackground) {
+    bgID = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
+      [[UIApplication sharedApplication] endBackgroundTask:bgID];
+    }];
+  }
+
   dispatch_async(_storageQueue, ^{
     // Check that a backend implementation is available for this target.
     NSInteger target = event.target;
@@ -99,6 +107,12 @@ - (void)storeEvent:(GDTEvent *)event {
     if (event.qosTier == GDTEventQoSFast) {
       [self.uploader forceUploadForTarget:target];
     }
+
+    // If running in the background, save state to disk and end the associated background task.
+    if (bgID != UIBackgroundTaskInvalid) {
+      [NSKeyedArchiver archiveRootObject:self toFile:[GDTStorage archivePath]];
+      [[UIApplication sharedApplication] endBackgroundTask:bgID];
+    }
   });
 }
 
@@ -180,6 +194,29 @@ - (void)addEventToTrackingCollections:(GDTStoredEvent *)event {
   _targetToEventSet[event.target] = events;
 }
 
+#pragma mark - GDTLifecycleProtocol
+
+- (void)appWillForeground:(UIApplication *)app {
+  [NSKeyedUnarchiver unarchiveObjectWithFile:[GDTStorage archivePath]];
+  self->_runningInBackground = NO;
+}
+
+- (void)appWillBackground:(UIApplication *)app {
+  self->_runningInBackground = YES;
+  [NSKeyedArchiver archiveRootObject:self toFile:[GDTStorage archivePath]];
+  // Create an immediate background task to run until the end of the current queue of work.
+  __block UIBackgroundTaskIdentifier bgID = [app beginBackgroundTaskWithExpirationHandler:^{
+    [app endBackgroundTask:bgID];
+  }];
+  dispatch_async(_storageQueue, ^{
+    [app endBackgroundTask:bgID];
+  });
+}
+
+- (void)appWillTerminate:(UIApplication *)application {
+  [NSKeyedArchiver archiveRootObject:self toFile:[GDTStorage archivePath]];
+}
+
 #pragma mark - NSSecureCoding
 
 /** The NSKeyedCoder key for the storedEvents property. */

GoogleDataTransport/GoogleDataTransport/Classes/GDTTransformer.h

@@ -16,6 +16,8 @@
 
 #import <Foundation/Foundation.h>
 
+#import <GoogleDataTransport/GDTLifecycle.h>
+
 @class GDTEvent;
 
 @protocol GDTEventTransformer;
@@ -28,7 +30,7 @@ NS_ASSUME_NONNULL_BEGIN
  * maintain state (or at least, there's nothing to stop them from doing that) and the same instances
  * may be used across multiple instances.
  */
-@interface GDTTransformer : NSObject
+@interface GDTTransformer : NSObject <GDTLifecycleProtocol>
 
 /** Instantiates or returns the event transformer singleton.
  *
@@ -37,6 +39,9 @@ NS_ASSUME_NONNULL_BEGIN
 + (instancetype)sharedInstance;
 
 /** Writes the result of applying the given transformers' -transform method on the given event.
+ *
+ * @note If the app is suspended, a background task will be created to complete work in-progress,
+ * but this method will not send any further events until the app is resumed.
  *
  * @param event The event to apply transformers on.
  * @param transformers The list of transformers to apply.

GoogleDataTransport/GoogleDataTransport/Classes/GDTTransformer.m

@@ -21,6 +21,7 @@
 
 #import "GDTAssert.h"
 #import "GDTConsoleLogger.h"
+#import "GDTLifecycle.h"
 #import "GDTStorage.h"
 
 @implementation GDTTransformer
@@ -46,6 +47,13 @@ - (instancetype)init {
 - (void)transformEvent:(GDTEvent *)event
       withTransformers:(NSArray<id<GDTEventTransformer>> *)transformers {
   GDTAssert(event, @"You can't write a nil event");
+
+  __block UIBackgroundTaskIdentifier bgID = UIBackgroundTaskInvalid;
+  if (_runningInBackground) {
+    bgID = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
+      [[UIApplication sharedApplication] endBackgroundTask:bgID];
+    }];
+  }
   dispatch_async(_eventWritingQueue, ^{
     GDTEvent *transformedEvent = event;
     for (id<GDTEventTransformer> transformer in transformers) {
@@ -61,7 +69,34 @@ - (void)transformEvent:(GDTEvent *)event
       }
     }
     [self.storageInstance storeEvent:transformedEvent];
+    if (self->_runningInBackground) {
+      [[UIApplication sharedApplication] endBackgroundTask:bgID];
+    }
+  });
+}
+
+#pragma mark - GDTLifecycleProtocol
+
+- (void)appWillForeground:(UIApplication *)app {
+  dispatch_async(_eventWritingQueue, ^{
+    self->_runningInBackground = NO;
   });
 }
 
+- (void)appWillBackground:(UIApplication *)app {
+  // Create an immediate background task to run until the end of the current queue of work.
+  __block UIBackgroundTaskIdentifier bgID = [app beginBackgroundTaskWithExpirationHandler:^{
+    [app endBackgroundTask:bgID];
+  }];
+  dispatch_async(_eventWritingQueue, ^{
+    [app endBackgroundTask:bgID];
+  });
+}
+
+- (void)appWillTerminate:(UIApplication *)application {
+  // Flush the queue immediately.
+  dispatch_sync(_eventWritingQueue, ^{
+                });
+}
+
 @end

GoogleDataTransport/GoogleDataTransport/Classes/GDTUploadCoordinator.h

@@ -16,14 +16,16 @@
 
 #import <Foundation/Foundation.h>
 
+#import <GoogleDataTransport/GDTLifecycle.h>
+
 #import "GDTRegistrar.h"
 
 NS_ASSUME_NONNULL_BEGIN
 
 /** This class connects storage and uploader implementations, providing events to an uploader
  * and informing the storage what events were successfully uploaded or not.
  */
-@interface GDTUploadCoordinator : NSObject
+@interface GDTUploadCoordinator : NSObject <NSSecureCoding, GDTLifecycleProtocol>
 
 /** Creates and/or returrns the singleton.
  *