Objective-C

One question I keep hearing is “Can you find out what music track a user is listening to? as I want to use it for …”, where the reason usually revolves around posting it to a social network network site, or using it as IM status. Thankfully retrieving the currently being played music track is very easy thanks to the MediaPlayer Framework.

Each application has its own MPMusicPlayerController, but it also has access to the iPod’s MPMusicPlayerController, using the class method iPodMusicPlayer.


MPMusicPlayerController *iPodMusicPlayerController = [MPMusicPlayerController iPodMusicPlayer];


After you have got the iPod music player, you can then get the now playing item

MPMediaItem *nowPlayingItem = [iPodMusicPlayerController nowPlayingItem];


If the now playing item is nil, you know that the user is not playing a music track on their iPod.

Unlike many of the other APIs in iOS, you can’t access information such as the track name, via a simple string property. You have to use one of the following keys:

NSString *const MPMediaItemPropertyPersistentID;
NSString *const MPMediaItemPropertyMediaType;
NSString *const MPMediaItemPropertyTitle;
NSString *const MPMediaItemPropertyAlbumTitle;
NSString *const MPMediaItemPropertyArtist;
NSString *const MPMediaItemPropertyAlbumArtist;
NSString *const MPMediaItemPropertyGenre;
NSString *const MPMediaItemPropertyComposer;
NSString *const MPMediaItemPropertyPlaybackDuration;
NSString *const MPMediaItemPropertyAlbumTrackNumber;
NSString *const MPMediaItemPropertyAlbumTrackCount;
NSString *const MPMediaItemPropertyDiscNumber;
NSString *const MPMediaItemPropertyDiscCount;
NSString *const MPMediaItemPropertyArtwork;
NSString *const MPMediaItemPropertyLyrics;
NSString *const MPMediaItemPropertyIsCompilation;
NSString *const MPMediaItemPropertyReleaseDate;
NSString *const MPMediaItemPropertyBeatsPerMinute;
NSString *const MPMediaItemPropertyComments;
NSString *const MPMediaItemPropertyAssetURL;


And then query the Media Player Item, using the instance method valueForProperty:.

NSString *itemTitle = [nowPlayingItem valueForProperty:MPMediaItemPropertyTitle];


And thus you will end up with a code snippet like this:


MPMusicPlayerController *iPodMusicPlayerController = [MPMusicPlayerController iPodMusicPlayer];

As always this is just a small code snippet to get you started. There are situations for instance, where the user can have a now playing item that has no title (strange I know). So as always you will have to handle these edge cases appropriately.

Location, Location, Location is all the rage at the moment. Where did someone last update their social network status ? Where is the nearest restaurant ? Where do I need to be in 5 mins ? the possibilities for location services are (nearly) endless. But what is a location ? well put simple it is just a co-ordinate value (longitude and latitude), and in the case of iPhone, it is in reference to the earth. But lets be honest, displaying -122.03, 37.33 in your sexy new iPhone application is not very exciting now is it ? That is were MKMapView comes in.

MKMapView allows you to display a Map on your iPhone’s screen. MKMapView is just a subclass of UIView so you can treat it like one. You can ether use it as a subview (such as on a profile page), or make it go full screen (using it with its own view controller) such as when you are viewing a map to get directions.

So like UIView, to create a MKMapView you need to initialise one with a frame:

MKMapView *mapView = [[MKMapView alloc] initWithFrame:CGRectMake(0,0,320,480)];


Unlike UIView, you will also want to become the delegate of MKMapView.


mapView.delegate = self;


The delegate methods for MKMapView include ones that inform you about when the map starts and finishes to load, in addition to if it fails to load at all. (These delegate methods are very similar to UIWebView if you have used that).


- (void)mapViewWillStartLoadingMap:(MKMapView *)mapView;
- (void)mapViewDidFinishLoadingMap:(MKMapView *)mapView;
- (void)mapViewDidFailLoadingMap:(MKMapView *)mapView withError:(NSError *)error;


In addition to the loading of the Map, the delegate also provides call backs for when the map’s region changes, it also provides callbacks regarding annotation information (more on that later).


- (void)mapView:(MKMapView *)mapView regionWillChangeAnimated:(BOOL)animated;
- (void)mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated;


After you have created a MKMapView, you will want to show a specific region on the map. The method to do this is:


- (void)setRegion:(MKCoordinateRegion)region animated:(BOOL)animated;


This introduces a new MapKit data type MKCoordinateRegion. This is the centre point (that you want to show) expressed as a co-ordinate, and then the distance (span) around this co-ordinate that you want to be shown. In essence the span is the zoom level. The bigger the span, the bigger the area that is displayed on the map.

To make a new region you will need to use:


MKCoordinateRegionMake(CLLocationCoordinate2D centerCoordinate, MKCoordinateSpan span);


And thus you will probably have some code that looks like this:


CLLocationCoordinate2D coordinate;
coordinate.latitude = -122.03;
coordinate.longitude = 37.33;

[mapView setRegion:MKCoordinateRegionMake(coordinate, MKCoordinateSpanMake(0.003, 0.003)) animated:YES];


After you have focused in on a specific region of the map, you will more than likely want to annotate a given point. To do this you need to create an object that conforms to the (informal) MKAnnotation protocol, and in particular implements the CLLocationCoordinate2D coordinate property.

e.g.


@interface MCSMMapAnnotation : NSObject {

@end


Then you just need to create an instance of this model object, and then add it to the map as an annotation:


MCSMMapAnnotation *annotation = [[MCSMMapAnnotation alloc] init];

And that is it, nice and simple.

One more thing …

Before I mentioned that there are delegate methods regarding the annotations on the Map View. One that is particular useful is:

- (void)mapView:(MKMapView *)mapView didAddAnnotationViews:(NSArray *)annotationViews;


Why is it useful ? Well if you didn’t notice, doing the above means that the annotation(s) just appear on the screen and they do not drop on. So in this delegate method, you can move the annotations off screen and then put them back to where MapKit said they should be.


- (void)mapView:(MKMapView *)mapView didAddAnnotationViews:(NSArray *)annotationViews{

}


This is just a brief overview of what you can do with MapKit. The most obvious thing you can do, is to add more than one annotation to the map, and the above animation trick is designed to work with this. One feature you may want to do if your application heavily relies upon maps, is to create your own custom pins (that don’t even need to look like pins), to point out specific points on the map.

Although for complex animation sequences on the iPhone you need to use either the OpenGL or Apple’s very own Core Animation Framework, a lot of simple animations can be achieved with the methods found in the UIView class. All these animations are actually built upon Core Animation, but they have been wrapped up for you to use with very little code.

All animations triggered by the UIView class happen within a animation block.

To start an animation block you use the UIView Class method:

+ (void)beginAnimations:(NSString *)animationID context:(void *)context;


The animation ID is used in delegate call backs for such things as the beginning and end of animation blocks. The context is an additional piece of information that can be passed through.

As both of these parameters are optional, you comenly see:

[UIView beginAnimations:@"" context:NULL];


To commit these animations, and therefore end the animation block, you need to use the UIView class method:

+ (void)commitAnimations


So what types of animations can you do ? well quite a few.

You can animate views by:

• Changing their alpha
• Changing there size
• Changing there location

In a single animation block you can animate multiple views, and you are also able to nest animation blocks.

So lets do a common example. When a UITableViewCell is being edited you often want to make a UILabel’s (label) alpha change to 0 so it is hidden:

For those new to C programming:

(editing ? 0.0 : 1.0)


Is equivlant to:

if(editing)
{
0.0;
}else{
1.0;
}


So for the second example we also have a UILabel (label), that we want to grow when the animation code is run. We also want this animation to last 2 seconds, so the user can admire our work. In addition to this, we want the animation to “ease in”. This is known as the animation curve. The animation curves that are available are

• ease in (slow then fast)
• ease out (fast then slow)
• ease in and out (slow, fast, slow)
• linear (constant speed)

We would do this animation using the following animation block:

This is just a brief overview of the animations you can do using the UIView class, but it should be enough to get you started. The UIView methods also include delegate call backs for when an animation starts and end. For more information see Apple’s Documentation.

If the UIView class does not have what you need, you will probably need to use the Core Animation framework. While using this framework is not trivial, it is not as hard as using OpenGL (which is used commonly for 3D games), and you can build some fantastic animations using it.