UISlider未更新

Question

我正在尝试为一项任务编写一个音乐播放器，并且我被困在试图让滑块随着歌曲的播放而更新。我已经能够做到这一点，如果用户滑动滑块，歌曲将倒带/快进到歌曲的该部分。有人知道为什么在播放歌曲时滑块不会持续更新吗？

这是.h文件

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

@interface AS3MPViewController : UIViewController <MPMediaPickerControllerDelegate>{
    IBOutlet UIButton *playButton;
    IBOutlet UIButton *stopButton;
    IBOutlet UIButton *pauseButton;
    IBOutlet UISlider *volumeSlider;
    AVAudioPlayer *musicPlayer;
    IBOutlet UIButton *pickSongButton;
    IBOutlet UISlider *timeSlider;
    NSTimer *timer;
}

@property (nonatomic, retain) UIButton *playButton;
@property (nonatomic, retain) UIButton *stopButton;
@property (nonatomic, retain) UIButton *pauseButton;
@property (nonatomic, retain) UISlider *volumeSlider;
@property (nonatomic, retain) AVAudioPlayer *musicPlayer;
@property (nonatomic, retain) UIButton *pickSongButton;
@property (nonatomic, retain) UISlider *timeSlider;
@property (nonatomic, retain) NSTimer *timer;

- (IBAction) play;
- (IBAction) stop;
- (IBAction) pause;
- (IBAction) changeVolume: (UISlider *)sender;
- (IBAction) chooseSong: (UIButton *)sender;
- (IBAction) changeTime: (UISlider *)sender;
- (void)setTimeSliderOptions;

@end

这是.m文件

#import "AS3MPViewController.h"

@interface AS3MPViewController ()

@end

@implementation AS3MPViewController

@synthesize playButton = _playButton;
@synthesize stopButton = _stopButton;
@synthesize pauseButton = _pauseButton;
@synthesize musicPlayer = _musicPlayer;
@synthesize volumeSlider = _volumeSlider;
@synthesize pickSongButton = _pickSongButton;
@synthesize timeSlider = _timeSlider;
@synthesize timer;

- (void)viewDidLoad
{
    [super viewDidLoad];

    NSString *filePath = [[NSBundle mainBundle] pathForResource:@"animals001"     ofType:@"mp3"];

    NSURL *fileURL = [[NSURL alloc] initFileURLWithPath:filePath];

    self.musicPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:fileURL error:nil];

    [self.musicPlayer prepareToPlay];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


- (IBAction) play {
    [self.musicPlayer play];

}

- (IBAction) stop {
    [self.musicPlayer stop];
    self.musicPlayer.currentTime = 0;
}

- (IBAction) pause {
    [self.musicPlayer pause];
}

- (IBAction) changeVolume: (UISlider *)sender {
    self.musicPlayer.volume = [sender value];
}

- (IBAction)chooseSong:(UIButton *)sender {
    MPMediaPickerController *mediaPicker = [[MPMediaPickerController alloc] initWithMediaTypes:MPMediaTypeAnyAudio];

    [mediaPicker setDelegate:self];
    [mediaPicker setAllowsPickingMultipleItems:NO];

    mediaPicker.prompt = NSLocalizedString(@"Add Some Songs To Play", "Prompt In Media Item Picker");

    [self presentModalViewController: mediaPicker animated:YES];
}

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

- (void) mediaPicker:(MPMediaPickerController *)mediaPicker didPickMediaItems:    (MPMediaItemCollection *)mediaItemCollection {

    MPMediaItem *item = [[mediaItemCollection items] objectAtIndex:0];
    NSURL *url = [item valueForProperty:MPMediaItemPropertyAssetURL];

    //AVPlayerItem *playerItem = [[AVPlayerItem alloc] initWithURL:url];
    //AVPlayer *player = [[AVPlayer alloc] initWithPlayerItem:playerItem];

    self.timeSlider.maximumValue = [self.musicPlayer duration];

    self.musicPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:url error:nil];

    [self.musicPlayer play];

    timer = [NSTimer scheduledTimerWithTimeInterval:0.1f target:self selector:@selector(songCurrentTime) userInfo:nil repeats:YES];

    [self dismissModalViewControllerAnimated:YES];
}

- (IBAction)changeTime: (UISlider *)sender {
    self.musicPlayer.currentTime = self.musicPlayer.duration * sender.value;
}

- (void)songCurrentTime {
    timeSlider.value = (self.musicPlayer.currentTime / self.musicPlayer.duration);
}
@end

Answer 1

检查连接，确保您使用ValueChanged EX的滑块连接了IBAction方法：

- (IBAction)changeTime: (UISlider *)sender {

IB连接时检查此方法是否与ValueChanged连接

Answer 2

我认为您的问题是您正在从一个线程而不是主线程更新滑块的值。尝试修改songCurrentTime方法，使其在更新滑块的值的主线程上调用另一个方法。

- (void)songCurrentTime {
[self performSelectorOnMainThread:@selector(songCurrentTimeMain) withObject:nil waitUntilDone:YES];
}

- (void)songCurrentTimeMain {
timeSlider.value = (self.musicPlayer.currentTime / self.musicPlayer.duration);
}

当然，为了获得正确的结果，请确保滑块的最小值为0，最大值为1。

诚挚的问候

Answer 3

设置滑块值时，该值始终小于或等于1，因为self.musicPlayer.currentTime始终小于或等于self.musicPlayer.duration。相反，你可以试试这个

timeSlider.value = self.musicPlayer.currentTime;