Iphone Application : Implementing Location Services - Creating a Location-Aware Application (part 1)

Many iPhone and Mac users have a, shall we say, “heightened” interest in Apple Computer; visiting Apple’s campus in Cupertino, California, can be a life-changing experience. For these special users, we’re going to create a Core Location-powered application that keeps you informed of just how far away you are.

The application will be created in two parts: The first introduces Core Location and displays the number of miles from the current location to Cupertino. In the second section, we use the iPhone’s compass to display an arrow that points users in the right direction, should they get off track.

Setting Up the Project

For the rest of this hour, we’ll be working on a new application that uses the Core Location framework. Create a new view-based iPhone application in Xcode and call it Cupertino.

Adding the Core Location Framework

The Core Location framework isn’t linked into our project by default, so we need to add it. Open the Targets group in Xcode, and right-click the Cupertino target. Right-click the Frameworks group in the Cupertino project, and then choose Add, Existing Frameworks from the contextual menu. Scroll through the Framework list that appears and find CoreLocation.framework. Select it, and then click Add to add it to the project, as shown in Figure 1. If it doesn’t add directly to the Frameworks group, drag the CoreLocation.framework icon into the group to keep the project tidy.

Figure 1. Add the Core Location framework to the project.

Adding Background Image Resources

To make sure the user remembers where we’re going, we have a nice picture of an apple as the application’s background image. Locate apple.png within the project’s Images folder in the Finder, and drag it into the Resources group within the Xcode project group. Be sure to check the Copy Items into Destination Group’s Folder check box in the Copy dialog. (You can also include the [email protected] file if you want a higher-resolution version for the iPhone 4’s display.)

Adding Outlets, Properties, and Protocols

The CupertinoViewController will serve as the location manager delegate, receiving location updates and updating the user interface to reflect the new locations. Click the CupertinoViewController.h file in the Classes group. Update the file by importing the Core Location header file, indicating that we’ll be conforming to the CLLocationManagerDelegate protocol, and adding properties for the location manager (locMan), a label with the distance to Cupertino (distanceLabel), and two subviews (distanceView and waitView), as demonstrated in Listing 1.

Listing 1.

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

@interface CupertinoViewController : UIViewController
    <CLLocationManagerDelegate> {

        CLLocationManager *locMan;
        IBOutlet UILabel *distanceLabel;
        IBOutlet UIView *distanceView;
        IBOutlet UIView *waitView;

}

@property (assign, nonatomic) CLLocationManager *locMan;
@property (retain, nonatomic) UILabel *distanceLabel;
@property (retain, nonatomic) UIView *distanceView;
@property (retain, nonatomic) UIView *waitView;

@end

For each of the properties, add a corresponding @synthesize line to the CupertinoViewController.m implementation file, following the @implementation directive:

@synthesize locMan;
@synthesize distanceLabel;
@synthesize distanceView;
@synthesize waitView;

Finally, add a release for each of these objects to the implementation file’s dealloc method:

- (void)dealloc {
    [locMan release];
    [distanceLabel release];
    [distanceView release];
    [waitView release];
    [super dealloc];
}

Creating the User Interface

The user interface for this hour’s lesson is simple: We can’t perform any actions to change our location (teleportation isn’t yet possible), so all we need to do is update the screen to show information about where we are.

Double-click the CupertinoViewController.xib file in the Resources group to open Interface Builder, and then complete the following steps:

The final view should resemble Figure 3. When satisfied with your results, save the XIB file and return to Xcode.

Figure 3. The final Cupertino Locator UI.