Size an MKMapView to Fit its Annotations in iOS Without Futzing with Coordinate Systems

map viewAn oddity of MKMapView is that it always defaults to showing the western hemisphere of the Earth. That’s almost certainly not what you want. Instead, you have probably set an array of id <MKAnnotation> objects which you want to appear as pins on the map. If the pins were evenly distributed over the USA, then great. Otherwise, the MapView is not at all zoomed the way you want. It baffles me a map view doesn’t just zoom itself by default when you set annotations, but it doesn’t.

One approach might be to loop over all of your annotations and figure out what the max and min x and y values are across them all. Then get the center point of the map view and do some math to convert the coordinates and scale the map view.

Alternatively, MapKit has API that is separate from the map view itself for manipulating rectangles and regions which can do the job automatically.

The main problem is that id <MKAnnotation> objects contain a CoreLocation coordinate – CLLocationCoordinate2D – which represents a GPS coordinate while MapView has an MKCoordinateRegion which has a CLLocationCoordinate2D defining its center but uses an MKCoordinateRegion span struct to define the zoom level of the map view in terms of degrees of arc.

MapKit provides a mix of object-oriented API and C functions to convert an array of CLLocationCoordinate2D structs from id <MKAnnotation> objects into an MKCoordinateRegion suitable for setting the region in a MKMapView. These transformations are straightforward and don’t require fiddling with converting between coordinate systems.

Here is the code in a map view controller

#define MINIMUM_ZOOM_ARC 0.014 //approximately 1 miles (1 degree of arc ~= 69 miles)
#define ANNOTATION_REGION_PAD_FACTOR 1.15
#define MAX_DEGREES_ARC 360
//size the mapView region to fit its annotations
- (void)zoomMapViewToFitAnnotations:(MKMapView *)mapView animated:(BOOL)animated
{ 
    NSArray *annotations = mapView.annotations;
    int count = [mapView.annotations count];
    if ( count == 0) { return; } //bail if no annotations
    
    //convert NSArray of id <MKAnnotation> into an MKCoordinateRegion that can be used to set the map size
    //can't use NSArray with MKMapPoint because MKMapPoint is not an id
    MKMapPoint points[count]; //C array of MKMapPoint struct
    for( int i=0; i<count; i++ ) //load points C array by converting coordinates to points
    {
        CLLocationCoordinate2D coordinate = [(id <MKAnnotation>)[annotations objectAtIndex:i] coordinate];
        points[i] = MKMapPointForCoordinate(coordinate);
    }
    //create MKMapRect from array of MKMapPoint
    MKMapRect mapRect = [[MKPolygon polygonWithPoints:points count:count] boundingMapRect];
    //convert MKCoordinateRegion from MKMapRect
    MKCoordinateRegion region = MKCoordinateRegionForMapRect(mapRect);
    
    //add padding so pins aren't scrunched on the edges
    region.span.latitudeDelta  *= ANNOTATION_REGION_PAD_FACTOR;
    region.span.longitudeDelta *= ANNOTATION_REGION_PAD_FACTOR;
    //but padding can't be bigger than the world
    if( region.span.latitudeDelta > MAX_DEGREES_ARC ) { region.span.latitudeDelta  = MAX_DEGREES_ARC; }
    if( region.span.longitudeDelta > MAX_DEGREES_ARC ){ region.span.longitudeDelta = MAX_DEGREES_ARC; }
    
    //and don't zoom in stupid-close on small samples
    if( region.span.latitudeDelta  < MINIMUM_ZOOM_ARC ) { region.span.latitudeDelta  = MINIMUM_ZOOM_ARC; }
    if( region.span.longitudeDelta < MINIMUM_ZOOM_ARC ) { region.span.longitudeDelta = MINIMUM_ZOOM_ARC; }
    //and if there is a sample of 1 we want the max zoom-in instead of max zoom-out
    if( count == 1 )
    { 
        region.span.latitudeDelta = MINIMUM_ZOOM_ARC;
        region.span.longitudeDelta = MINIMUM_ZOOM_ARC;
    }
    [mapView setRegion:region animated:animated];
}

- (void)viewWillAppear:(BOOL)animated
{
    [self zoomMapViewToFitAnnotations:self.mapView animated:animated];
    //or maybe you would do the call above in the code path that sets the annotations array
}

How to Create an Xcode 4.0-style Window-based Application in Xcode 4.2

I’ve decided to get up to speed on iOS programming and, to help me with that, I bought Aaron Hillegass’s iOS Programming: The Big Nerd Ranch Guid 2nd edition. I’ve listened to Aaron on podcasts and have heard that his training method is fantastic. The book does seem to be unusually well written for a tech book but the problem I immediately ran into is that it was written for Xcode 4.0 and iOS 4.3 SDK. I have Lion with Xcode 4.2 and iOS 5 SDK. That’s part of the adventure of discovery and change in tech but unfortunately Apple removed the project type that Hillegass’s examples are based on which is a major stumbling block.

Hillegass uses the “Window-based Application” template for iOS as the basis for all of his projects. That template no longer exists in Xcode. The closest thing in Xcode 4.2 is “Empty Application”. However, that’s not quite the same thing because the now-defunct “Window-based Application” template generated a main window XIB view wired to generated controller but the “Empty Application” has no XIB. In order to make any sense out of the book, you have to create the XIB and wire it up yourself. This is no big deal to anybody with a little experience but to a newb like me, it took a bit of wandering in the wilderness at the Big Nerd Ranch forums to figure out how to manually get the project into the state that the exercises in the book will work.

How to Convert a new “Empty Application” into a “Window-based Application”

Start by creating a new iOS Application project using the “Empty Application” project. This will create a very similar project to the “Window-based Application” project described in iOS Programming 2/e with just a few differences:

  1. The main controller class that gets generated is “AppDelegate” rather than “<project-name>AppDelegate”. The
  2. There is no XIB view.
  3. The window property of AppDelegate doesn’t have the IBOutlet macro to make it visible to the Interface Builder tooling.
    1. Prepare the controller to talk to the Interface Builder tooling

    In the controller class interface definition of the we need to add the IBOutlet macro so that the tooling will recognize the controller. In your controller header file, AppDelegate.h, the line to modify begins with @property and ends with *window. Add IBOutlet in front of the UIWindow type as shown below.

#import <UIKit/UIKit.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) IBOutlet UIWindow *window;

@end

Save this change.

Update the didFinishLaunchingWithOptions: method

The auto-generated first line of code in the didFinishLaunchingWithOptions: method of AppDelegate.m prevents message routing from working properly. Comment it out as below:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    //self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];
    // Override point for customization after application launch.
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;
}

Save this change.

Create the XIB file

Right-click on the folder containing your AppDelegate files and choose “Add File”. Select “Window” from the iOS User Interface group. Choose the appropriate device family—for the initial Quiz project that is iPhone. The default file name is Window.xib which works fine or you can name it MainWindow.xib to make it just like in the book.

OS X 10.7 (Lion)-2011-11-23-11-18-56

Change the Class of the XIB file’s owner to UIApplication

Select Window.xib in the Navigator. Select the “File’s Owner” cube in the objects pane just left of the layout canvas and change the Class in the properties pane to UIApplication.

OS X 10.7 (Lion)-2011-11-23-11-34-47

 

Add an object for the controller

Filter the tool pallet on the bottom right to “Objects and Controllers” and drag and drop an Object from the toolbox onto the object pane.

OS X 10.7 (Lion)-2011-11-23-11-37-52

Set the class of the controller object

In the properties window, change the class to controller that was generated for your project by the template. That should be AppDelegate. The Object will automatically be renamed with a space added into the Pascal casing. (You can override this by putting something into the Label field of the Identity pane.)

OS X 10.7 (Lion)-2011-11-23-11-45-00

Route the XIB delegate to the controller

Now we want to wire up the MVC message routing for the view. Select the “File’s Owner” cube in the object pane and control+drag the delegate outlet to the App Delegate object.

OS X 10.7 (Lion)-2011-11-23-12-00-15

 

Route the controller object’s window outlet to the window object

Next perform a similar ctrl+drag of the window outlet from the App Delegate object to the Window object.

OS X 10.7 (Lion)-2011-11-23-12-01-08

All done

Now our Empty Application project is set up just like a Window-based Application as described in iOS Programming 2nd Edition. The file names may be a bit different but that should have no practical  effect. The AppDelegate inherits from UIResponder <UIApplicationDelegate> rather than NSObject<UIApplicationDelegate>. This doesn’t seem to be a problem, either.

Now that I have figured out how to create an wire up a main window XIB file, everything seems to work great as I follow along in the book.

Replicating My Key Android App Features on iOS

PwnTunes-IconPwnTunes (€10) == Android Mass Storage USB Device

Android is mostly cloud-focused. You don’t sync it with a PIM or iTunes. If you want to put music on the Nexus One or get your pictures off you can just plug it into a computer. Android presents itself as a USB drive.  You can simply copy files back and forth between the device and the computer. Incidentally, this is exactly how the Kindle and my Nikon D200 work as well.

PwnTunes is a Cydia app which requires that your iPhone is jailbroken but it pretty much replicates the Android behavior. I was willing to pay €10 for this convenience because I’m an iTunes rebel. I buy my music from Amazon’s MP3 store and I don’t even have iTunes installed on my Windows partition where I spend the vast majority of my time.

PwnTunes Update

PwnTunes is horrible. It does not work well at all. Unfortunately, there is no substitute for iTunes for i-devices.

bria-iconBria iPhone App ($8) == SipDroid

I have a SIP account on Callcentric which allows me to make calls in the US without any international phone charges when I’m abroad. My SIP account is also tied to my Google Voice number so when I get a call on my main USA number it rings through to me anywhere in the world provided that my phone has data service. Bria is working really well for me so far. I’d say that the background service and notification features of Android  is more favorable to this sort of thing. It does seem that iOS will occasionally decide to kill Bria, I think. It’s hard to tell.

gvoice-iconGoogle Voice == Google Voice

Apple has approved the Google Voice app for iOS so it is now available on the iPhone. Incidentally, the iTunes store on iOS makes this much easier to install than the Android Market because if your SIM is not on one of the whitelisted carriers in Google Market, Google Voice doesn’t appear. The iTunes store has no such issue.

Podcaster ($2) == Google Listenpodcaster-icon

Google Listen is a podcatcher which downloads and caches podcasts over the air. It’s a little flaky but it mostly works. It’s another one of the apps that is hidden in Google Market for some carriers. Podcaster does the same thing for iOS and has a much nicer user interface than Google Listen. I really like Podcaster but my main complaint is that the scheduled polling of podcasts doesn’t seem to be reliable when Podcaster is running in the background.

kindle-iconKindle == Kindle

On the one hand this is essentially the same reading experience as the Android version. On the other hand, the Android version is more feature-ful because of the subscription content struggle between Amazon and Apple. The iOS version of Kindle cannot receive periodical subscriptions.

 

nytimes-iconNY Times == NY Times

Nothing to see here. The Android and iOS versions are nearly identical if you allow for the differences in standard interface widgets on the platforms.

 

gtranslate-icon

Google Translate == Google Translate

Again this is the same app on iOS as on Android. It’s very cool if a bit Eurocentric. Don’t expect it to hear and speak Arabic or Asanti Twi. On the other hand it is great at hearing and speaking French, Spanish, German and Dutch. It speaks Danish but can’t hear Danish and it hears Afrikaans but can’t speak it. Something interesting is going on there.

Bonus: Flickrflickr-icon

iOS has a cool Flickr app that will background upload photos to your Flickr stream and can also edit tags and sets in Flickr as well as browse your friends Flickr streams. Nicely done.

 

Bonus: OneNote

onenote-icon

I have OneNote and use it off and on. OneNote 2010 syncs with Microsoft’s cloud storage and this cool little iOS app also syncs with Microsoft’s cloud storage. If you take notes on an iDevice they show up in OneNote on Windows and vice-versa. My main complaint is that syncing a notebook for the first time is pretty slow over 3g. Jury is still out on this one but I’m giving it a whirl.

Nexus One Came Back to Life After a Soaking

I’ve had my Nexus One in a bag of rice for the last 5 days to draw the water out of it. I put the battery back in this morning and it booted up with a working touch screen and no evident ill effects except that it has decided to erase all my personal data and apps.

All of the data on it is synced onto cloud services and onto my iPhone and desktop so nothing is lost. It is a big hassle to get apps back on the Nexus One though because the Android Market store has some really unfortunate carrier blocking. Some apps such as GMail, Google Listen, Google Voice and Amazon Kindle do not appear in the store unless the carrier identified by your SIM is white-listed with Google. This is one thing that Apple seems to get really right. The iOS App Store seems to work regardless of locality or carrier.

I’ve decided to stick with iPhone for a while. iOS 4 is a significant improvement. It seems to achieve most of the key benefits that Android has while retaining a slicker GUI and avoiding the glitchy touch-screen registration issues and periodic hangs that I experience regularly with Android 2.2 on the Nexus One.

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