在任务之间留出时间 - iOS

Question

我正在通过 iPhone 的 GPS 获取我的位置信息。我想从同一点获取坐标 15 次（以获得最佳水平精度）。

有没有办法等待，例如，一个坐标和另一个坐标之间的 2 秒？

我使用了一个叫做坐标的对象，以经纬度为属性。

.... Exemple code
Coordinate * coord = [[Coordinate alloc] init];
NSMutableArray *coordinates = [[NSMutableArray alloc] init];

for (i=0 ; i<=14; i++)
{
    coord = newlocation;
    [coordinates addObject:coord];
    .... some code to wait 2 seconds before add a new object to the array....
}

我尝试使用NSThread sleepfortimeinterval，但视图冻结。

谢谢

Answer 1

而不是像这样使用for 循环，理论上您可以使用每两秒触发一次的重复NSTimer，然后在15 次迭代后使用invalidate 计时器。

但我不建议这样做，而是转向事件驱动模型，等待致电您的didUpdateLocations。如果 didUpdateLocations 尚未更新，则在两秒钟内检查是没有意义的。同样，在 30 秒内重复检查 15 次也是没有意义的，例如，如果您在 5 秒后获得了非常准确的位置。

我建议开始监控该位置，在随后调用didUpdateLocations 时观察这些位置，并检查CLLocation 中的horizontalAccuracy（它告诉您该位置的准确程度）。一旦达到所需的horizontalAccuracy，您就可以宣布成功（例如停止监视位置或其他）。如果需要，您还可以建立一个NSTimer，在 30 秒后自动关闭位置监控。

---

例如：

- (void)viewDidLoad
{
    [super viewDidLoad];

    NSLog(@"%s", __PRETTY_FUNCTION__);

    [self startStandardUpdates];

    // after 30 seconds, if we haven't found a location, declare success with whatever we got (if anything)

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(30.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        [self stopStandardUpdates];  // stop monitoring location if you want

        if (!self.foundLocation) {
            if (self.bestLocation) {
                NSLog(@"Didn't find perfect location, but location has accuracy of %.1f meters", self.bestLocation.horizontalAccuracy);
            } else {
                NSLog(@"Even after 30 seconds, did not find any locations!");
            }
        }
    });
}

#pragma mark - Location Services

- (void)startStandardUpdates
{
    // Create the location manager if this object does not
    // already have one.
    if (nil == self.locationManager)
        self.locationManager = [[CLLocationManager alloc] init];

    self.locationManager.delegate = self;
    self.locationManager.desiredAccuracy = kCLLocationAccuracyBest;

    // Set a movement threshold for new events.
    self.locationManager.distanceFilter = 5;

    [self.locationManager startUpdatingLocation];
}

- (void)stopStandardUpdates
{
    [self.locationManager stopUpdatingLocation];
    self.locationManager = nil;
}

#pragma mark - CLLocationManagerDelegate

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
{
    CLLocation* location = [locations lastObject];

    NSLog(@"%s: horizontalAccuracy = %.1f", __FUNCTION__, location.horizontalAccuracy);

    if (location.horizontalAccuracy < 0)  // not a valid location
        return;

    // this checks to see if the location is more accurate than the last;
    // or you might just want to eliminate this `if` clause, because if
    // you get updated location, you can probably assume it's better than
    // the last one (esp if the user might be moving)

    if (!self.bestLocation || location.horizontalAccuracy <= self.bestLocation.horizontalAccuracy) {
        self.bestLocation = location;
    }

    if (location.horizontalAccuracy <= 5) { // use whatever you want here
        NSLog(@"Found location %@", location);
        self.foundLocation = YES;
        [self stopStandardUpdates]; // stop it if you want
    }
}

这使用以下属性：

@property (nonatomic, strong) CLLocationManager *locationManager;
@property (nonatomic, strong) CLLocation *bestLocation;
@property (nonatomic) BOOL foundLocation;