播放音乐入门

大纲

这次简单实现了：

在线音乐播放（AVPlayer）、
监听进度（addPeriodicTimeObserverForInterval）、
设置控制中心的音乐信息（MPNowPlayingInfoCenter）、
监听远程控制中心的操作（remoteControlReceivedWithEvent上一曲、下一曲等）

还未涉及到的知识有：

AVAudioSession 等，慢慢完善。

效果图

Screen Shot 2018-01-30 at 下午4.26.10.png IMG_2141.PNG IMG_2142.PNG

代码

//
//  ViewController.m
//  LearnAVPlayer
//
//  Created by zhiyunyu on 2018/1/29.
//  Copyright © 2018年 zhiyunyu. All rights reserved.
//

#import "ViewController.h"
#import <AVFoundation/AVFoundation.h>
#import <MediaPlayer/MediaPlayer.h>

#define MP3_URL @"http://techslides.com/demos/samples/sample.mp3" //文件来源于 http://techslides.com/sample-files-for-development

@interface ViewController ()

@property(nonatomic, strong) UIButton *startPlayBtn;
@property(nonatomic, strong) UIProgressView *musicProgressView;

@property(nonatomic, strong) AVPlayer *player;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.view.backgroundColor = [UIColor blackColor];
    
    self.startPlayBtn = ({
        UIButton *btn = [[UIButton alloc] initWithFrame:CGRectMake(100, [UIScreen mainScreen].bounds.size.height - 200,[UIScreen mainScreen].bounds.size.width - 200, 48)];
        btn.layer.borderWidth = 1;
        btn.layer.cornerRadius = 24;
        btn.layer.borderColor = [UIColor whiteColor].CGColor;
        [btn setTitle:@"播放" forState:UIControlStateNormal];
        [btn addTarget:self action:@selector(startPlay:) forControlEvents:UIControlEventTouchUpInside];
        btn;
    });
    [self.view addSubview:self.startPlayBtn];
    
    self.musicProgressView = ({
        UIProgressView *progressView = [[UIProgressView alloc] initWithFrame:CGRectMake(24, [UIScreen mainScreen].bounds.size.height - 250,[UIScreen mainScreen].bounds.size.width - 48, 20)];
        progressView.backgroundColor = [UIColor whiteColor];
        progressView;
    });
    [self.view addSubview:self.musicProgressView];
    
    [self setMusicInfo];
}

-(void)setMusicInfo {
    NSURL * url  = [NSURL URLWithString:MP3_URL];
    AVPlayerItem * songItem = [[AVPlayerItem alloc]initWithURL:url];
    self.player = [[AVPlayer alloc]initWithPlayerItem:songItem];
    
//    @weakify(self); 我目前没有添加对应的库，正式工程中一定要加上@weakify(self);
    id observer = [self.player addPeriodicTimeObserverForInterval:CMTimeMake(10.0, 10.0) queue:dispatch_get_main_queue() usingBlock:^(CMTime time) {
//        @strongify(self);
        CGFloat currentTime = CMTimeGetSeconds(time);
        self.musicProgressView.progress = currentTime / CMTimeGetSeconds(self.player.currentItem.duration);
        [self updateNowPlayingInfoCenter];
    }];
    
    //告诉系统，我们要接受远程控制事件（如果这里不设置，即使设置了MPNowPlayingInfoCenter，控制中心也不会显示歌曲信息）
    [[UIApplication sharedApplication] beginReceivingRemoteControlEvents];
    [self becomeFirstResponder];
}

-(void)startPlay:(id)sender {
    [self.player play];
}

//设置控制中心的歌曲信息
-(void)updateNowPlayingInfoCenter {
    NSDictionary *info = @{MPMediaItemPropertyArtist:@"俞志云",
                           MPMediaItemPropertyAlbumTitle:@"一首歌的名字",
                           MPMediaItemPropertyPlaybackDuration:@(CMTimeGetSeconds(self.player.currentItem.duration)),
                           MPNowPlayingInfoPropertyElapsedPlaybackTime:@(CMTimeGetSeconds(self.player.currentTime))
                            };
    [[MPNowPlayingInfoCenter defaultCenter] setNowPlayingInfo:info];
}

//响应远程音乐播放控制消息
- (void)remoteControlReceivedWithEvent:(UIEvent *)receivedEvent {
    if (receivedEvent.type == UIEventTypeRemoteControl) {
        switch (receivedEvent.subtype) {
            case UIEventSubtypeRemoteControlPlay:
                NSLog(@"暂停播放");
                break;
            case UIEventSubtypeRemoteControlPause:
                NSLog(@"继续播放");
                break;
            case UIEventSubtypeRemoteControlNextTrack:
                NSLog(@"下一曲");
                break;
            case UIEventSubtypeRemoteControlPreviousTrack:
                NSLog(@"上一曲");
                break;
            default:
                break;
        }
    }
}

@end

关于background modes

要支持后台播放得设置background modes；
在控制中心显示歌曲信息不需要设置background modes ，但是歌曲播放完毕信息就不再显示；如果要歌曲信息一直驻留在控制中心，就得设置background modes ；
设置支持音频后台播放：选中项目》capability > background modes 〉勾选第一项audio （这是基本设置，可能还要多加一些操作，等我再确认下）