使用當前位置縮放MapView的問題

Question

我在我的應用程序的首頁上顯示地圖視圖，我使用CLLocation從當前位置設置區域和座標。 當應用程序運行時，藍圖正顯示在地圖視圖上，當我打開其子視圖並返回到主屏幕時，地圖將顯示完美的位置和縮放級別。 下面的代碼導致藍屏是否有任何錯誤？

- (void)viewWillAppear:(BOOL)animated { 
    CLLocationManager *lm = [[CLLocationManager alloc] init]; 
    lm.delegate = self; 
    lm.desiredAccuracy = kCLLocationAccuracyBest; 
    lm.distanceFilter = kCLDistanceFilterNone; 
    [lm startUpdatingLocation]; 

    CLLocation *location = [lm location]; 

    CLLocationCoordinate2D coord; 


    coord = [location coordinate]; 

    CLLocationCoordinate2D zoomLocation; 
    zoomLocation.latitude = coord.latitude; //39.281516; 
    zoomLocation.longitude= coord.longitude; //-76.580806; 

    MKCoordinateRegion viewRegion = MKCoordinateRegionMakeWithDistance(zoomLocation, 0.3*METERS_PER_MILE, 0.3*METERS_PER_MILE); 

    MKCoordinateRegion adjustedRegion = [self.mainMapView regionThatFits:viewRegion];     

    [self.mainMapView setRegion:adjustedRegion animated:YES];  
} 

Answer 1

我猜你會看到藍色，因爲位置是（0，0），它位於大海中間。可能因爲第一次，CLLocationManager的位置尚未設置。

您應該檢查是否還有位置，如果沒有，請等待CLLocationManagerDelegate方法locationManager:didUpdateToLocation:fromLocation:中的回調，然後將地圖居中放置在所需位置。

事情是這樣的：

... 
@property (nonatomic, assign) BOOL needsCentering 
... 

@synthesize needsCentering = _needsCentering; 

- (void)viewWillAppear:(BOOL)animated { 
    CLLocationManager *lm = [[CLLocationManager alloc] init]; 
    lm.delegate = self; 
    lm.desiredAccuracy = kCLLocationAccuracyBest; 
    lm.distanceFilter = kCLDistanceFilterNone; 
    [lm startUpdatingLocation]; 

    CLLocation *location = [lm location]; 

    if (!location) { 
     _needsCentering = YES; 
    } else { 
     _needsCentering = NO; 

     CLLocationCoordinate2D coord; 

     coord = [location coordinate]; 

     CLLocationCoordinate2D zoomLocation; 
     zoomLocation.latitude = coord.latitude; //39.281516; 
     zoomLocation.longitude= coord.longitude; //-76.580806; 

     MKCoordinateRegion viewRegion = MKCoordinateRegionMakeWithDistance(zoomLocation, 0.3*METERS_PER_MILE, 0.3*METERS_PER_MILE); 

     MKCoordinateRegion adjustedRegion = [self.mainMapView regionThatFits:viewRegion];     

     [self.mainMapView setRegion:adjustedRegion animated:YES]; 
    } 
} 

- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation { 
    if (_needsCentering) { 
     _needsCentering = NO; 

     CLLocationCoordinate2D coord; 

     coord = [newLocation coordinate]; 

     CLLocationCoordinate2D zoomLocation; 
     zoomLocation.latitude = coord.latitude; //39.281516; 
     zoomLocation.longitude= coord.longitude; //-76.580806; 

     MKCoordinateRegion viewRegion = MKCoordinateRegionMakeWithDistance(zoomLocation, 0.3*METERS_PER_MILE, 0.3*METERS_PER_MILE); 

     MKCoordinateRegion adjustedRegion = [self.mainMapView regionThatFits:viewRegion];     

     [self.mainMapView setRegion:adjustedRegion animated:YES]; 
    } 
} 

但同時，你可能想看看的MKMapViewshowsUserLocation。