Classes/TeslameterViewController.m

/*
    File: TeslameterViewController.m
Abstract: A view controller that manages the primary view within the application. It creates a CLLocationManager and turns on heading updates. As updates are received, it displays them in a graph, x, y, and z labels, and also computes the magnitude (size or strength) of the magnetic vector. The units for all values are microteslas.
 
 Version: 1.2
 
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*/
 
#import "TeslameterViewController.h"
#import "GraphView.h"
 
@implementation TeslameterViewController
 
@synthesize magnitudeLabel;
@synthesize xLabel;
@synthesize yLabel;
@synthesize zLabel;
@synthesize graphView;
 
@synthesize locationManager;
 
- (void)viewDidLoad {
    [super viewDidLoad];
    
    // setup the location manager
    self.locationManager = [[[CLLocationManager alloc] init] autorelease];
    
    // check if the hardware has a compass
    if ([CLLocationManager headingAvailable] == NO) {
        // No compass is available. This application cannot function without a compass, 
        // so a dialog will be displayed and no magnetic data will be measured.
        self.locationManager = nil;
        UIAlertView *noCompassAlert = [[UIAlertView alloc] initWithTitle:@"No Compass!" message:@"This device does not have the ability to measure magnetic fields." delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
        [noCompassAlert show];
        [noCompassAlert release];
    } else {
        // heading service configuration
        locationManager.headingFilter = kCLHeadingFilterNone;
        
        // setup delegate callbacks
        locationManager.delegate = self;
        
        // start the compass
        [locationManager startUpdatingHeading];
    }
}
 
- (void)viewDidUnload {
    self.magnitudeLabel = nil;
    self.xLabel = nil;
    self.yLabel = nil;
    self.zLabel = nil;
    self.graphView = nil;
}
 
- (void)dealloc {
    [magnitudeLabel release];
    [xLabel release];
    [yLabel release];
    [zLabel release];
    [graphView release];
    
    // Stop the compass
    [locationManager stopUpdatingHeading];
    [locationManager release];
    [super dealloc];
}
 
// This delegate method is invoked when the location manager has heading data.
- (void)locationManager:(CLLocationManager *)manager didUpdateHeading:(CLHeading *)heading {
    // Update the labels with the raw x, y, and z values.
    [xLabel setText:[NSString stringWithFormat:@"%.1f", heading.x]];
    [yLabel setText:[NSString stringWithFormat:@"%.1f", heading.y]];
    [zLabel setText:[NSString stringWithFormat:@"%.1f", heading.z]];
    
    // Compute and display the magnitude (size or strength) of the vector.
    //      magnitude = sqrt(x^2 + y^2 + z^2)
    CGFloat magnitude = sqrt(heading.x*heading.x + heading.y*heading.y + heading.z*heading.z);
    [magnitudeLabel setText:[NSString stringWithFormat:@"%.1f", magnitude]];
    
    // Update the graph with the new magnetic reading.
    [graphView updateHistoryWithX:heading.x y:heading.y z:heading.z];
}
 
// This delegate method is invoked when the location managed encounters an error condition.
- (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error {
    if ([error code] == kCLErrorDenied) {
        // This error indicates that the user has denied the application's request to use location services.
        [manager stopUpdatingHeading];
    } else if ([error code] == kCLErrorHeadingFailure) {
        // This error indicates that the heading could not be determined, most likely because of strong magnetic interference.
    }
}
 
@end