將CLGeocoder城市名稱傳遞給新類UILabel

Question

我正在嘗試將CLGeocoder檢索的城市名稱成功傳遞給另一個類的UILabel。首先，CLGecoder級

FindLocation.h

@property (nonatomic, strong) NSString *cityName; 

FindLocation.m - 裏法（無效）的LocationManager：（CLLocationManager *）經理...

- (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它看起來像這樣：

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

我不知道這裏有什麼錯。既然找到了城市，後面的代碼肯定會出錯，但我不知道是什麼。 NSString - cityName的傳遞是否實現了錯誤？

Answer 1

我認爲問題在於地理編碼過程不是即時的。您正在實例化FindLocation，然後立即嘗試訪問cityName。但是，即使假設您的init方法觸發位置更新，地理編碼器也需要一點時間才能訪問服務器並獲得響應。另外，位置管理器不會立即返回一個位置，並且由於它看起來像是地理編碼器的起始位置，所以您必須稍等一會。

這裏的一個解決方案是在FindLocation上實現委託協議，以便在地理編碼完成時通知FirstViewController。事情是這樣的：

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 

，然後在CLGeocoder completionHandler檢索的cityName後：現在

[self.delegate findLocationDidGeocodeCityName:self.cityName]; 

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

@interface FirstViewController : UIViewController <FindLocationDelegate> 

在你的FirstViewCont roller.m，設置委託像這樣：

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

，然後也FirstViewController，實現委託方法：

#pragma mark - FindLocation Delegate 

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

還有其他的方法來做到這一點爲好，但關鍵是你必須等到completionHandler運行，然後通知其他感興趣的對象返回什麼。