CLLocation 标头始终为 -1

Question

嘿伙计们，我正在尝试构建一个应用程序，它将使用指南针指向预定位置的方向，但现在我正在尝试了解如何制作基本指南针。我遵循了指南，但是我总是得到“-1”作为标题，并且只让它工作一次，从那以后我就没有更改过代码。任何想法都会有帮助。

#import <UIKit/UIKit.h>
#import <CoreLocation/CoreLocation.h>

@interface TrackerViewController : UIViewController <CLLocationManagerDelegate> {

}

@property (nonatomic, retain) CLLocationManager *locationManager;
@property (nonatomic, retain) IBOutlet UISwitch *toggle;
@property (nonatomic, retain) IBOutlet UIImageView *compass;
@property (nonatomic, retain) IBOutlet UILabel *headingLabel;

-(IBAction)toggleSwitch;

@end

以及实施文件...

#import "TrackerViewController.h"


@implementation TrackerViewController

@synthesize locationManager; 
@synthesize toggle; 
@synthesize compass; 
@synthesize headingLabel;

- (IBAction)toggleSwitch {
if(self.toggle.isOn) {
    [self.locationManager startUpdatingHeading];
} else {
    [self.locationManager stopUpdatingHeading];
}
}

- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];

if ([CLLocationManager headingAvailable]) {
    self.locationManager = [[[CLLocationManager alloc] init] autorelease]; 
    self.locationManager.delegate = self;
} else {
    [[[[UIAlertView alloc] initWithTitle:@"Aw snap!" 
                                 message:@"Device doesn't support heading updates" 
                                delegate:nil 
                       cancelButtonTitle:@"OK" 
                       otherButtonTitles:nil] autorelease] show];   
}
}

- (void)locationManager:(CLLocationManager *)manager didUpdateHeading:(CLHeading 
*)newHeading {
float heading = [newHeading trueHeading] * M_PI / 180.0;
self.compass.transform = CGAffineTransformMakeRotation(-heading);
self.headingLabel.text = [NSString stringWithFormat:@"%d°", (int)[newHeading trueHeading]];
NSLog(@"%d", (int)[newHeading trueHeading]);
}


- (void)locationManager:(CLLocationManager *)manager 
   didFailWithError:(NSError *)error {

//  NSLog(@"Error!");

if (error.code == kCLErrorDenied) {
    [[[[UIAlertView alloc] initWithTitle:@"Aw snap!" 
                                 message:@"User didn't allow heading updates" 
                                delegate:nil 
                       cancelButtonTitle:@"OK" 
                       otherButtonTitles:nil] autorelease] show];
    self.toggle.on = NO;
    [self.locationManager stopUpdatingHeading];
}
}


- (void)didReceiveMemoryWarning {
// Releases the view if it doesn't have a superview.
[super didReceiveMemoryWarning];

// Release any cached data, images, etc that aren't in use.
}

- (void)viewDidUnload {
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
}


- (void)dealloc {
self.locationManager = nil;
self.compass = nil;
self.toggle = nil;
self.headingLabel = nil;
[super dealloc];
}

@end

Answer 1

磁航向
该属性中的值表示相对于磁北极的航向，这与地理北极不同。值 0 表示设备指向磁北，90 表示设备指向东，180 表示设备指向南，依此类推。此属性中的值应始终有效。