iOS挂起时间

AppDelegate
@property(nonatomic,strong)NSDate * backgroundDate;

- (void)applicationDidEnterBackground:(UIApplication *)application {
    
    self.backgroundDate = [NSDate date];
}
- (void)applicationDidBecomeActive:(UIApplication *)application {
    NSDate * currentDate = [NSDate date];
    NSTimeInterval start = [self.backgroundDate timeIntervalSince1970]*1;
    NSTimeInterval end = [currentDate timeIntervalSince1970]*1;
    
     NSTimeInterval value = end - start;
    NSLog(@"时间差%f",value);
}