【代码笔记】获取系统完成任务所需的后台时间

#import <UIKit/UIKit.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

//添加变量
@property (assign, nonatomic) UIBackgroundTaskIdentifier backgroundUpdateTask;

@end

#import "AppDelegate.h"
#import "RootViewController.h"

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    
    RootViewController *rootVC=[[RootViewController alloc]init];
    UINavigationController *nav=[[UINavigationController alloc]initWithRootViewController:rootVC];
    self.window.rootViewController=nav;
    
    
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;
}

- (void)applicationWillResignActive:(UIApplication *)application
{
    // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
    // Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
}

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    
    [self beingBackgroundUpdateTask];
    // 在这里加上你需要长久运行的代码
    
    //最后彻底的还一次。
    [self endBackgroundUpdateTask];
    
}

- (void)beingBackgroundUpdateTask
{
    self.backgroundUpdateTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
        //有借有还。
        [self endBackgroundUpdateTask];
    }];
}
- (void)endBackgroundUpdateTask
{
    [[UIApplication sharedApplication] endBackgroundTask: self.backgroundUpdateTask];
    self.backgroundUpdateTask = UIBackgroundTaskInvalid;
}