将CLGeocoder城市名称传递给新类UILabel

Question

我正在尝试将CLGeocoder检索的城市名称成功传递给另一个类的UILabel。首先，CLGecoder级

FindLocation.h

@property (nonatomic, strong) NSString *cityName; 

FindLocation.m - 里法（无效）的LocationManager：（CLLocationManager *）经理...

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations 
{ 
if (self.isFirstUpdate) { 
    self.isFirstUpdate = NO; 
    return; 
} 

CLLocation *location = [locations lastObject]; 

if (location.horizontalAccuracy > 0) { 
    self.currentLocation = location;} 

CLGeocoder *fgeo = [[CLGeocoder alloc] init]; 

// Reverse Geocode a CLLocation to a CLPlacemark 
[fgeo reverseGeocodeLocation:location completionHandler:^(NSArray *placemarks, NSError 
*error){ 
    NSLog(@"%@", location); 

       // Make sure the geocoder did not produce an error 
       // before continuing 
       if(!error){ 
        // Iterate through all of the placemarks returned 
        // and output them to the console 

        for(CLPlacemark *placemark in placemarks){ 
         NSLog(@"%@",[placemark description]); 
         self.cityName = [placemark locality]; 
         NSLog(@"city is %@",cityName); } 

        [self.locationManager stopUpdatingLocation]; 
        [self.delegate findLocationDidGeocodeCityName:self.cityName]; 
       } else { 
        // Our geocoder had an error, output a message 
        // to the console 
        NSLog(@"There was a reverse geocoding error\n%@", 
         [error localizedDescription]); 

而且在我FirstViewController它看起来像这样：

FindLocation *cityname = [[FindLocation alloc] init]; 
    [cityname cityName]; 
    [self.cityLabel setText:(cityname.cityName)]; 
    NSLog(@"CityName is...%@", cityname.cityName); //Log shows CityName is...(null) 

我不知道这里有什么错。既然找到了城市，后面的代码肯定会出错，但我不知道是什么。 NSString - cityName的传递是否实现了错误？

Answer 1

我认为问题在于地理编码过程不是即时的。您正在实例化FindLocation，然后立即尝试访问cityName。但是，即使假设您的init方法触发位置更新，地理编码器也需要一点时间才能访问服务器并获得响应。另外，位置管理器不会立即返回一个位置，并且由于它看起来像是地理编码器的起始位置，所以您必须稍等一会。

这里的一个解决方案是在FindLocation上实现委托协议，以便在地理编码完成时通知FirstViewController。事情是这样的：

FindLocation.h

#import <UIKit/UIKit.h> 

@class FindLocation; 
@protocol FindLocationDelegate <NSObject> 
- (void)findLocationDidGeocodeCityName:(NSString *)cityName; 
@end 

@interface FindLocation : NSObject 

@property (weak, nonatomic) id<FindLocationDelegate> delegate; 

@end 

，然后在CLGeocoder completionHandler检索的cityName后：现在

[self.delegate findLocationDidGeocodeCityName:self.cityName]; 

，在FirstviewController.h，表明您符合FindLocationDelegate协议：

@interface FirstViewController : UIViewController <FindLocationDelegate> 

在你的FirstViewCont roller.m，设置委托像这样：

FindLocation *cityName = [[FindLocation alloc] init]; 
cityName.delegate = self; 

，然后也FirstViewController，实现委托方法：

#pragma mark - FindLocation Delegate 

- (void)findLocationDidGeocodeCityName:(NSString *)cityName 
{ 
    [self.cityLabel setText:cityName]; 
} 

还有其他的方法来做到这一点为好，但关键是你必须等到completionHandler运行，然后通知其他感兴趣的对象返回什么。