Question

I am trying to make an app that plays MP3 songs. My program flow is like this:

I have an XML file here in my website: http://jeewanaryal.web44.net/SongsXML/songsListXML.xml. It has song titles and the actual URL of those songs on the Internet. I have the following code for my Pop songs section:

NSString *urlString = @"http://jeewanaryal.web44.net/SongsXML/songsListXML.xml";
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:urlString]];

NSDictionary *dict = [XMLReader dictionaryForXMLData:data error:nil];

NSArray *arrayOfSongs = [[NSArray alloc] initWithArray:[[[dict objectForKey:@"list"] objectForKey:@"songs"] objectForKey:@"song"]];


StartStopSound = [UIButton buttonWithType:UIButtonTypeRoundedRect];
StartStopSound.frame = CGRectMake(60, 360, 200, 30);
[StartStopSound setTitle:@"बजाउनुहोस" forState:UIControlStateNormal];
[StartStopSound addTarget:self action:@selector(playSong) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:StartStopSound];

back = [UIButton buttonWithType:UIButtonTypeRoundedRect];
back.frame = CGRectMake(20, 320, 100, 30);
[back setTitle:@"पछाडीको गीत " forState:UIControlStateNormal];
[back addTarget:self action:@selector(playSong) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:back];

next = [UIButton buttonWithType:UIButtonTypeRoundedRect];
next.frame = CGRectMake(200, 320, 100, 30);
[next setTitle:@"अगाडीको गीत" forState:UIControlStateNormal];
[next addTarget:self action:@selector(playSong) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:next];



NSData *myData = [[NSData alloc] init ];
NSString *urlString1 = [[NSString alloc] init];


for (NSDictionary *fruitDict in arrayOfSongs) {

    UILabel *songTitle = [[UILabel alloc] initWithFrame:CGRectMake(40, 200, 300, 40)];
    songTitle.text = [NSString stringWithFormat:@"%@",[[fruitDict objectForKey:@"title"] objectForKey:@"text"]];
    [self.view addSubview:songTitle];


    urlString1 = [NSString stringWithFormat:@"%@",[[fruitDict objectForKey:@"url"] objectForKey:@"text"]];



    //NSLog(@"\n\n -- URL STRING : %@ \n\n",urlString);

}

myData = [NSData dataWithContentsOfURL:[NSURL URLWithString:urlString1]];

player = [[AVAudioPlayer alloc] initWithData:myData error:nil];

[player play];
[player numberOfLoops];
[player currentTime];

This works fine for a single song; that is, it only plays the last URL of my XML file. I want to make all songs to be played one by one, making a “Next” and “Previous” button on my app.

Will you please tell me how I can implement that? I am using XMLReader.h and XMLReader.m file to parse the data from XML into my app.

Answer 1

You would need to store arrayOfSongs somewhere in the class. The “back” and “next” buttons would need separate actions (e.g. playPreviousSong, playNextSong). These methods would then look something like this:

-(void) playPreviousSong
{
    NSString *url = [[self songs] objectAtIndex:[self songIndex] - 1];
    [self playSong:url];
    [self setSongIndex:[self songIndex - 1];
}

This is a crude implementation just to show how it’d fit together. Basically you need to store the list of songs and keep track of which song is “selected”/playing, then just select the next/previous one.

Edit: To answer your question in the comments, you have already extracted the array of song URLs, you simply need to keep a reference to it in the class. E.g.

@interface AudioPlayer {
    NSArray *_songs;
    NSUInteger *_songIndex;
}

Then in the @implementation instead of creating a arrayOfSongs variable, simply reference the array from the instance variable:

_songs = [[NSArray alloc] initWithArray:[[[dict objectForKey:@"list"] objectForKey:@"songs"] objectForKey:@"song"]];

Then in, for example, the playPreviousSong method:

-(void) playPreviousSong
{
    NSString *url = [_songs objectAtIndex:_songIndex - 1];
    [self playSong:url];
    _songIndex--;
}