【代碼筆記】獲取系統完成任務所需的後臺時間

一，代碼。

AppDelegate.h

#import <UIKit/UIKit.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

//添加變數
@property (assign, nonatomic) UIBackgroundTaskIdentifier backgroundUpdateTask;

@end

AppDelegate.m

#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];
    // 在這裡加上你需要長久運行的代碼
    
    //最後徹底的還一次。
    [self endBackgroundUpdateTask];
    
}

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