Added MYBackgroundMonitor

MYBackgroundMonitor.h

@@ -0,0 +1,43 @@
+//
+//  MYBackgroundMonitor.h
+//  MYUtilities
+//
+//  Created by Jens Alfke on 9/24/15.
+//  Copyright © 2015 Jens Alfke. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+
+
+/** Monitors when a UIKit app enters/leaves the background, and allows the client to start a
+    "background task" to request more time to finish an activity. */
+@interface MYBackgroundMonitor : NSObject
+
+- (instancetype) init;
+
+/** Explicitly stops the monitor. (So does deallocing it.) */
+- (void) stop;
+
+/** Starts a background task. Should be called from the onAppBackgrounding block.
+    Only one background task can be active at a time. */
+- (BOOL) beginBackgroundTaskNamed: (NSString*)name;
+
+/** Tells the OS that the current background task is done. */
+- (void) endBackgroundTask;
+
+/** YES if there is currently a background task. */
+@property (readonly) BOOL hasBackgroundTask;
+
+/** This block will be called when the app goes into the background.
+    The app will soon stop being scheduled for CPU time unless the block starts a background task
+    by calling -beginBackgroundTaskNamed:. */
+@property (strong) void (^onAppBackgrounding)();
+
+/** Called when the app returns to the foreground. */
+@property (strong) void (^onAppForegrounding)();
+
+/** Called if the OS loses its patience before -endBackgroundTask is called.
+    The task is implicitly ended, and the app will soon stop being scheduled for CPU time. */
+@property (strong) void (^onBackgroundTaskExpired)();
+
+@end

MYBackgroundMonitor.m

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+//
+//  MYBackgroundMonitor.m
+//  MYUtilities
+//
+//  Created by Jens Alfke on 9/24/15.
+//  Copyright © 2015 Jens Alfke. All rights reserved.
+//
+
+#import "MYBackgroundMonitor.h"
+#import <UIKit/UIKit.h>
+#import <dispatch/dispatch.h>
+
+
+@implementation MYBackgroundMonitor
+{
+    NSString* _name;
+    UIBackgroundTaskIdentifier _bgTask;
+}
+
+
+@synthesize onAppBackgrounding=_onAppBackgrounding, onAppForegrounding=_onAppForegrounding;
+@synthesize onBackgroundTaskExpired=_onBackgroundTaskExpired;
+
+
+- (instancetype) init {
+    self = [super init];
+    if (self) {
+        _bgTask = UIBackgroundTaskInvalid;
+        [[NSNotificationCenter defaultCenter] addObserver: self
+                                                 selector: @selector(appBackgrounding:)
+                                                 name: UIApplicationDidEnterBackgroundNotification
+                                               object: nil];
+        [[NSNotificationCenter defaultCenter] addObserver: self
+                                                 selector: @selector(appForegrounding:)
+                                                 name: UIApplicationWillEnterForegroundNotification
+                                               object: nil];
+    }
+    return self;
+}
+
+
+- (void) endBackgroundTask {
+    @synchronized(self) {
+        if (_bgTask != UIBackgroundTaskInvalid) {
+            [[UIApplication sharedApplication] endBackgroundTask: _bgTask];
+            _bgTask = UIBackgroundTaskInvalid;
+        }
+    }
+}
+
+
+- (void) stop {
+    [self endBackgroundTask];
+    [[NSNotificationCenter defaultCenter] removeObserver: self];
+}
+
+
+- (void) dealloc {
+    [self stop];
+}
+
+
+- (BOOL) beginBackgroundTaskNamed: (NSString*)name {
+    @synchronized(self) {
+        Assert(_bgTask == UIBackgroundTaskInvalid);
+        _bgTask = [[UIApplication sharedApplication] beginBackgroundTaskWithName: name
+                                                               expirationHandler: ^{
+            // Process ran out of background time before endBackgroundTask was called:
+            [self endBackgroundTask];
+            if (_onBackgroundTaskExpired)
+                _onBackgroundTaskExpired();
+        }];
+        return (_bgTask != UIBackgroundTaskInvalid);
+    }
+}
+
+
+- (BOOL) hasBackgroundTask {
+    @synchronized(self) {
+        return _bgTask != UIBackgroundTaskInvalid;
+    }
+}
+
+
+- (void) appBackgrounding: (NSNotification*)n {
+    if (_onAppBackgrounding)
+        _onAppBackgrounding();
+}
+
+
+- (void) appForegrounding: (NSNotification*)n {
+    if (_onAppForegrounding)
+        _onAppForegrounding();
+}
+
+
+@end