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