如何等待，直到位置管理器來獲得高精確的數據

Question

我有這樣的代碼要等待一段時間才能獲得高準確的數據：

-(void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation{ 

    if((newLocation.horizontalAccuracy < 150 && newLocation.horizontalAccuracy > 0 /* valid */ && abs(howRecent) < 15.0 /*If it's a relatively recent event less than 15 seconds */)) 


} 

在我的應用程序的其他部分的問題，我需要等待這種方法要回來，所以我用：

[NSThread sleepForTimeInterval:5]; // wait 5 seconds 

這是一個很好的做法，或者有更好的方式來等待另一個任務的執行。

Answer 1

Apple已經提供了一個示例項目，演示了這種確切的場景。 該項目名爲LocateMe和can be found here。

你可以在GetLocationViewController.m找到相關的方法。

簡而言之，它背後的邏輯是放棄任何緩存值並累積位置讀數，直到horizontalAccuracy符合desiredAccuracy要求。我希望這會讓你走上正軌。

Answer 2

#import "LocationTracker.h" 

#define LATITUDE @"latitude" 
#define LONGITUDE @"longitude" 
#define ACCURACY @"theAccuracy" 

#define IS_OS_8_OR_LATER ([[[UIDevice currentDevice] systemVersion] floatValue] >= 8.0) 

@implementation LocationTracker 
AppDelegate *objApp; 


+ (CLLocationManager *)sharedLocationManager { 
    static CLLocationManager *_locationManager; 

    @synchronized(self) { 
     if (_locationManager == nil) { 
      _locationManager = [[CLLocationManager alloc] init]; 
      _locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation; 
     } 
    } 
    return _locationManager; 
} 

- (id)init { 
    if (self==[super init]) { 
     //Get the share model and also initialize myLocationArray 
     self.shareModel = [LocationShareModel sharedModel]; 
     self.shareModel.myLocationArray = [[NSMutableArray alloc]init]; 

     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(applicationEnterBackground) name:UIApplicationDidEnterBackgroundNotification object:nil]; 
     objApp = (AppDelegate *)[[UIApplication sharedApplication] delegate]; 

    } 
    return self; 

} 

-(void)applicationEnterBackground{ 
    CLLocationManager *locationManager = [LocationTracker sharedLocationManager]; 
    locationManager.delegate = self; 
    locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation; 
    locationManager.distanceFilter = kCLDistanceFilterNone; 

    if(IS_OS_8_OR_LATER) { 
     [locationManager requestAlwaysAuthorization]; 
    } 
    [locationManager startUpdatingLocation]; 

    //Use the BackgroundTaskManager to manage all the background Task 
    self.shareModel.bgTask = [BackgroundTaskManager sharedBackgroundTaskManager]; 
    [self.shareModel.bgTask beginNewBackgroundTask]; 
} 

- (void) restartLocationUpdates 
{ 
    NSLog(@"restartLocationUpdates"); 

    if (self.shareModel.timer) { 
     [self.shareModel.timer invalidate]; 
     self.shareModel.timer = nil; 
    } 

    CLLocationManager *locationManager = [LocationTracker sharedLocationManager]; 
    locationManager.delegate = self; 
    locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation; 
    locationManager.distanceFilter = kCLDistanceFilterNone; 

    if(IS_OS_8_OR_LATER) { 
     [locationManager requestAlwaysAuthorization]; 
    } 
    [locationManager startUpdatingLocation]; 
} 


- (void)startLocationTracking { 
    NSLog(@"startLocationTracking"); 

    if ([CLLocationManager locationServicesEnabled] == NO) { 
     NSLog(@"locationServicesEnabled false"); 
     UIAlertView *servicesDisabledAlert = [[UIAlertView alloc] initWithTitle:@"Location Services Disabled" message:@"You currently have all location services for this device disabled" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil]; 
     [servicesDisabledAlert show]; 
    } else { 
     CLAuthorizationStatus authorizationStatus= [CLLocationManager authorizationStatus]; 

     if(authorizationStatus == kCLAuthorizationStatusDenied || authorizationStatus == kCLAuthorizationStatusRestricted){ 
      NSLog(@"authorizationStatus failed"); 
     } else { 
      NSLog(@"authorizationStatus authorized"); 
      CLLocationManager *locationManager = [LocationTracker sharedLocationManager]; 
      locationManager.delegate = self; 
      locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation; 
      locationManager.distanceFilter = kCLDistanceFilterNone; 

      if(IS_OS_8_OR_LATER) { 
       [locationManager requestAlwaysAuthorization]; 
      } 
      [locationManager startUpdatingLocation]; 
     } 
    } 
} 


- (void)stopLocationTracking { 
    NSLog(@"stopLocationTracking"); 

    if (self.shareModel.timer) { 
     [self.shareModel.timer invalidate]; 
     self.shareModel.timer = nil; 
    } 

    CLLocationManager *locationManager = [LocationTracker sharedLocationManager]; 
    [locationManager stopUpdatingLocation]; 
} 

#pragma mark - CLLocationManagerDelegate Methods 

-(void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations{ 

    NSLog(@"locationManager didUpdateLocations"); 

    for(int i=0;i<locations.count;i++){ 
     CLLocation * newLocation = [locations objectAtIndex:i]; 
     CLLocationCoordinate2D theLocation = newLocation.coordinate; 
     CLLocationAccuracy theAccuracy = newLocation.horizontalAccuracy; 

     NSTimeInterval locationAge = -[newLocation.timestamp timeIntervalSinceNow]; 

     if (locationAge > 30.0) 
     { 
      continue; 
     } 

     //Select only valid location and also location with good accuracy 
     if(newLocation!=nil&&theAccuracy>0 
      &&theAccuracy<2000 
      &&(!(theLocation.latitude==0.0&&theLocation.longitude==0.0))){ 

      self.myLastLocation = theLocation; 
      self.myLastLocationAccuracy= theAccuracy; 

      NSMutableDictionary * dict = [[NSMutableDictionary alloc]init]; 
      [dict setObject:[NSNumber numberWithFloat:theLocation.latitude] forKey:@"latitude"]; 
      [dict setObject:[NSNumber numberWithFloat:theLocation.longitude] forKey:@"longitude"]; 
      [dict setObject:[NSNumber numberWithFloat:theAccuracy] forKey:@"theAccuracy"]; 

      //Add the vallid location with good accuracy into an array 
      //Every 1 minute, I will select the best location based on accuracy and send to server 
      [self.shareModel.myLocationArray addObject:dict]; 
     } 
    } 

    //If the timer still valid, return it (Will not run the code below) 
    if (self.shareModel.timer) { 
     return; 
    } 

    self.shareModel.bgTask = [BackgroundTaskManager sharedBackgroundTaskManager]; 
    [self.shareModel.bgTask beginNewBackgroundTask]; 

    //Restart the locationMaanger after 1 minute 
    self.shareModel.timer = [NSTimer scheduledTimerWithTimeInterval:30 target:self 
                  selector:@selector(restartLocationUpdates) 
                  userInfo:nil 
                  repeats:NO]; 

    //Will only stop the locationManager after 10 seconds, so that we can get some accurate locations 
    //The location manager will only operate for 10 seconds to save battery 
    if (self.shareModel.delay10Seconds) { 
     [self.shareModel.delay10Seconds invalidate]; 
     self.shareModel.delay10Seconds = nil; 
    } 

    self.shareModel.delay10Seconds = [NSTimer scheduledTimerWithTimeInterval:10 target:self 
                selector:@selector(stopLocationDelayBy10Seconds) 
                userInfo:nil 
                repeats:NO]; 

} 


//Stop the locationManager 
-(void)stopLocationDelayBy10Seconds{ 
    CLLocationManager *locationManager = [LocationTracker sharedLocationManager]; 
    [locationManager stopUpdatingLocation]; 

    NSLog(@"locationManager stop Updating after 10 seconds"); 
} 


- (void)locationManager: (CLLocationManager *)manager didFailWithError: (NSError *)error 
{ 
    // NSLog(@"locationManager error:%@",error); 

    switch([error code]) 
    { 
     case kCLErrorNetwork: // general, network-related error 
     { 
      UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Network Error" message:@"Please check your network connection." delegate:self cancelButtonTitle:@"Ok" otherButtonTitles:nil, nil]; 
      [alert show]; 
     } 
      break; 
     case kCLErrorDenied:{ 
      UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Enable Location Service" message:@"You have to enable the Location Service to use this App. To enable, please go to Settings->Privacy->Location Services" delegate:self cancelButtonTitle:@"Ok" otherButtonTitles:nil, nil]; 
      [alert show]; 
     } 
      break; 
     default: 
     { 

     } 
      break; 
    } 
} 


//Send the location to Server 
- (void)updateLocationToServer { 

    NSLog(@"updateLocationToServer"); 

    // Find the best location from the array based on accuracy 
    NSMutableDictionary * myBestLocation = [[NSMutableDictionary alloc]init]; 

    for(int i=0;i<self.shareModel.myLocationArray.count;i++){ 
     NSMutableDictionary * currentLocation = [self.shareModel.myLocationArray objectAtIndex:i]; 

     if(i==0) 
      myBestLocation = currentLocation; 
     else{ 
      if([[currentLocation objectForKey:ACCURACY]floatValue]<=[[myBestLocation objectForKey:ACCURACY]floatValue]){ 
       myBestLocation = currentLocation; 
      } 
     } 
    } 
    NSLog(@"My Best location:%@",myBestLocation); 


    //If the array is 0, get the last location 
    //Sometimes due to network issue or unknown reason, you could not get the location during that period, the best you can do is sending the last known location to the server 
    if(self.shareModel.myLocationArray.count==0) 
    { 
     NSLog(@"Unable to get location, use the last known location"); 

     self.myLocation=self.myLastLocation; 
     self.myLocationAccuracy=self.myLastLocationAccuracy; 

    }else{ 
     CLLocationCoordinate2D theBestLocation; 
     theBestLocation.latitude =[[myBestLocation objectForKey:LATITUDE]floatValue]; 
     theBestLocation.longitude =[[myBestLocation objectForKey:LONGITUDE]floatValue]; 
     self.myLocation=theBestLocation; 
     self.myLocationAccuracy =[[myBestLocation objectForKey:ACCURACY]floatValue]; 
    } 

    NSLog(@"Send to Server: Latitude(%f) Longitude(%f) Accuracy(%f)",self.myLocation.latitude, self.myLocation.longitude,self.myLocationAccuracy); 

    //TODO: Your code to send the self.myLocation and self.myLocationAccuracy to your server 

    //After sending the location to the server successful, remember to clear the current array with the following code. It is to make sure that you clear up old location in the array and add the new locations from locationManager 
    [self.shareModel.myLocationArray removeAllObjects]; 
    self.shareModel.myLocationArray = nil; 
    self.shareModel.myLocationArray = [[NSMutableArray alloc]init]; 
} 




@end