iphone Programming : Integrating Your Application - Media Playback

Just as it has done for images with the UIImagePickerController class and for email with the MFMailComposeViewController class , Apple has provided a standard way to select and play back iPod media inside your own application.

Warning:

The MPMediaPickerController and associated classes make use of the iPod library; this is not present in iPhone Simulator and will work correctly only on the device itself.

However, things are a little bit more complicated than the two previous cases; here we use an MPMediaPickerController that, via the MPMediaPickerControllerDelegate protocol, returns an MPMediaItemCollection object containing the media items the user has selected, and that can be played using an MPMusicPlayerController object.

These classes are provided by the Media Player framework; if you want to use them, you must add the Media Player framework to your project by right-clicking the Frameworks group in Groups & Files and selecting Add→Existing Frameworks.

Let’s reuse the Prototype application. Open the Finder and navigate to the location where you saved the Prototype project. Right-click on the folder containing the project files and select Duplicate; a folder called Prototype copy will be created containing a duplicate of the project. 

Note:

To prune the Prototype application down to the stub, you will need to:

Next, open the PrototypeViewController.h interface file, import the Media Player framework into the interface (.h) files, and declare your class as an MPMediaPickerControllerDelegate:

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

@interface PrototypeViewController : UIViewController
  <MPMediaPickerControllerDelegate> {
    IBOutlet UIButton *goButton;
}

-(IBAction) pushedGo:(id)sender;

@end

Save your changes, and open the PrototypeViewController.m implementation file. In the pushedGo: method, instantiate an MPMediaPickerController object and present its view modally to the user:

-(IBAction) pushedGo:(id)sender {
   MPMediaPickerController *mediaPicker =
				[[MPMediaPickerController alloc]
				initWithMediaTypes: MPMediaTypeAnyAudio];
				mediaPicker.delegate = self;
				mediaPicker.allowsPickingMultipleItems = YES;
				[self presentModalViewController:mediaPicker animated:YES];
				[mediaPicker release];
}

Now implement the following two delegate methods:

- (void) mediaPicker:(MPMediaPickerController *) mediaPicker
  didPickMediaItems:(MPMediaItemCollection *) userMediaItemCollection
{
    [self dismissModalViewControllerAnimated: YES];

    MPMusicPlayerController *musicPlayer =
      [MPMusicPlayerController applicationMusicPlayer];
    [musicPlayer setQueueWithItemCollection: userMediaItemCollection];
    [musicPlayer play];
}

- (void) mediaPickerDidCancel: (MPMediaPickerController *) mediaPicker {
    [self dismissModalViewControllerAnimated: YES];
}

Save your changes, and click on the Build and Run button in the Xcode toolbar to build and deploy your code. Remember that you’ll need to configure your project  to allow you to deploy the application onto your iPhone or iPod touch so that you can test the application on your device.

Once your application loads, tap the Go! button to bring up the MPMediaPickerController, select some songs, and tap the Done button in the navigation bar (see Figure 1). Your music should start playing.

Once playback has begun, you need to keep track of the currently playing item and display that to the user, or at the very least provide some way for the user to pause (or stop) playback, or perhaps to change her selection. The MPMusicPlayerController class provides two methods: the beginGeneratingPlaybackNotifications: method and a corresponding endGeneratingPlaybackNotifications: method. Add this line to the didPickMediaItems: method:

- (void) mediaPicker:(MPMediaPickerController *) mediaPicker
  didPickMediaItems:(MPMediaItemCollection *) userMediaItemCollection {
    [self dismissModalViewControllerAnimated: YES];

    MPMusicPlayerController *musicPlayer =
      [MPMusicPlayerController applicationMusicPlayer];
    [musicPlayer setQueueWithItemCollection: userMediaItemCollection];
    [musicPlayer beginGeneratingPlaybackNotifications];
    [musicPlayer play];
}

When the begin method is invoked, the class will start to generate notifications of when the player state changes and when the current playback item changes, which your application can register to handle by adding itself as an observer using the NSNotificationCenter class:

- (void) mediaPicker:(MPMediaPickerController *) mediaPicker
  didPickMediaItems:(MPMediaItemCollection *) userMediaItemCollection {
    [self dismissModalViewControllerAnimated: YES];

    MPMusicPlayerController *musicPlayer =
    [MPMusicPlayerController applicationMusicPlayer];
    [musicPlayer setQueueWithItemCollection: userMediaItemCollection];
    [musicPlayer beginGeneratingPlaybackNotifications];

    NSNotificationCenter *notificationCenter =
				[NSNotificationCenter defaultCenter];
				[notificationCenter addObserver:self
				selector:@selector(handleNowPlayingItemChanged:)
				name:@"MPMusicPlayerControllerNowPlayingItemDidChangeNotification"
				object:musicPlayer];
				[notificationCenter addObserver:self
				selector:@selector(handlePlaybackStateChanged:)
				name:@"MPMusicPlayerControllerPlaybackStateDidChangeNotification"
				object:musicPlayer];

    [musicPlayer play];

}

This will invoke the selector methods in our class when the appropriate notification arrives. (You could, for example, use the first to update a UILabel in your view telling the user the name of the currently playing song.)

However, for now let’s just implement these methods to print messages to the console log. In the PrototypeViewController.h interface file, declare the selector methods:

@interface PrototypeViewController : UIViewController
  <MPMediaPickerControllerDelegate>
{
    IBOutlet UIButton *goButton;
}

-(IBAction) pushedGo:(id)sender;
- (void)handleNowPlayingItemChanged:(id)notification;
				- (void)handlePlaybackStateChanged:(id)notification;

@end

Then, in the PrototypeViewController.m implementation file, add the following method. This will be called when the current item being played changes:

- (void)handleNowPlayingItemChanged:(id)notification {
   MPMusicPlayerController *musicPlayer =
      [MPMusicPlayerController applicationMusicPlayer];
   MPMediaItem *currentItem = [musicPlayer nowPlayingItem];
   NSLog(@"%@", currentItem);
}

While the second method handles changes in state, we can use this to update our user interface (e.g., changing the state of the Play and Stop buttons when the music ends):

- (void)handlePlaybackStateChanged:(id)notification {
    MPMusicPlayerController *musicPlayer =
      [MPMusicPlayerController applicationMusicPlayer];
    MPMusicPlaybackState playbackState = [musicPlayer playbackState];
    if (playbackState == MPMusicPlaybackStatePaused) {
        NSLog(@"Paused");

    } else if (playbackState == MPMusicPlaybackStatePlaying) {
        NSLog(@"Playing");

    } else if (playbackState == MPMusicPlaybackStateStopped) {
        NSLog(@"Stopped");

    }
}

Save your changes, and click on the Build and Run button in the Xcode toolbar to build and deploy your code onto your device. Once your application loads, tap the Go! button to bring up the MPMediaPickerController again, select some songs, and tap the Done button in the navigation bar. Your music should start playing, but this time you should see something similar to the following log messages in the Debugger Console:

2009-12-11 00:29:42.535 Prototype[447:207] <MPMediaItem 0x1373e0>
 persistentID: 6817778870160863775
2009-12-11 00:29:42.685 Prototype[447:207] Playing