Question

我试图根据在MIDI播放期间传递用户事件时调用的用户事件回调的内容，弄清楚如何更新UI元素（UIImageViews）。更具体地说，这些用户事件包含传递给用户回调函数的音符数据（例如，演奏音符为60，即中间C）。

我想根据播放的音符更新我的UIImageViews。我试图从回调中访问UIImageViews，但由于它没有直接访问ViewController，并且因为它运行在主要线程以外的线程上，所以我被建议以不同的方式执行。

所以，我想要做的是创建一个单独的控制器，可以将信息从回调函数传递到UI，但我不知道该怎么做。我已经在下面发布了我的ViewController的代码。它包括回调函数和用于设置用户事件和其他视图相关内容的所有相关代码。

我正在使用iOS 5在Xcode 4.3.1中工作，而我正在使用ARC。

PracticeViewController.h

#import <UIKit/UIKit.h>
#import "Lesson.h"
#import "Note.h"
#import <AudioToolbox/AudioToolbox.h>

@interface PracticeViewController : UIViewController

@property (strong, nonatomic) Lesson *selectedLesson;
@property (strong, nonatomic) IBOutlet UINavigationItem *practiceWindowTitle;
@property MusicPlayer player;

//Outlets for White Keys
@property (strong, nonatomic) IBOutlet UIImageView *whiteKey21;
// […]
@property (strong, nonatomic) IBOutlet UIImageView *whiteKey108;

//Outlets for Black Keys
@property (strong, nonatomic) IBOutlet UIImageView *blackKey22;
// […]
@property (strong, nonatomic) IBOutlet UIImageView *blackKey106;

// Key Highlight Images
@property (strong, nonatomic) UIImage *highlightA;
@property (strong, nonatomic) UIImage *highlightB;
@property (strong, nonatomic) UIImage *highlightC;
@property (strong, nonatomic) UIImage *highlightD;
@property (strong, nonatomic) UIImage *highlightE;
@property (strong, nonatomic) UIImage *highlightF;
@property (strong, nonatomic) UIImage *highlightG;
@property (strong, nonatomic) UIImage *highlightH;

- (IBAction)practiceLesson:(id)sender;

@end

PracticeViewController.m

#import "PracticeViewController.h"

@interface PracticeViewController ()

@end

@implementation PracticeViewController
@synthesize blackKey22;
// […]
@synthesize blackKey106;
@synthesize whiteKey21;
// […]
@synthesize whiteKey108;

@synthesize selectedLesson, practiceWindowTitle, player, highlightA, highlightB, highlightC, highlightD, highlightE, highlightF, highlightG, highlightH;

// Implement the UserEvent structure.

typedef struct UserEvent {
    UInt32 length;
    UInt32 typeID;
    UInt32 trackID;
    MusicTimeStamp tStamp;
    MusicTimeStamp dur;
    int playedNote;
} UserEvent;

// Implement the UserCallback function.

void noteUserCallback (void *inClientData, MusicSequence inSequence, MusicTrack inTrack, MusicTimeStamp inEventTime, const MusicEventUserData *inEventData, MusicTimeStamp inStartSliceBeat, MusicTimeStamp inEndSliceBeat)
{       
    UserEvent* event = (UserEvent *)inEventData;
    UInt32 size = event->length;
    UInt32 note = event->playedNote;
    UInt32 timestamp = event->tStamp;
    NSLog(@"Size: %lu Note: %lu, Timestamp: %lu", size, note, timestamp);
}

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }

    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.practiceWindowTitle.title = selectedLesson.titleAndSubtitle;

    // Load in the images for the glow.
    highlightA = [UIImage imageNamed:@"glow_whiteKeysA.png"];
    highlightB = [UIImage imageNamed:@"glow_whiteKeysB.png"];
    highlightC = [UIImage imageNamed:@"glow_whiteKeysC.png"];
    highlightD = [UIImage imageNamed:@"glow_whiteKeysD.png"];
    highlightE = [UIImage imageNamed:@"glow_whiteKeysE.png"];
    highlightF = [UIImage imageNamed:@"glow_whiteKeysF.png"];
    highlightG = [UIImage imageNamed:@"glow_blackKey.png"];
    highlightH = [UIImage imageNamed:@"glow_whiteKeysH.png"];

    // Create player, sequence, left/right hand tracks, and iterator.

    NewMusicPlayer(&player);
    MusicSequence sequence;
    NewMusicSequence(&sequence);
    MusicTrack rightHand;
    MusicTrack leftHand;
    MusicEventIterator iterator;

    // Load in MIDI file.

    NSString *path = [[NSString alloc] init];
    path = [[NSBundle mainBundle] pathForResource:selectedLesson.midiFilename ofType:@"mid"];
    NSURL *url = [NSURL fileURLWithPath:path];
    MusicSequenceFileLoad(sequence, (__bridge CFURLRef)url, 0, kMusicSequenceLoadSMF_ChannelsToTracks);

    // Get the right and left hand tracks from the sequence.

    int rightHandIndex = 0;
    //int leftHandIndex = 1;

    MusicSequenceGetIndTrack(sequence, rightHandIndex, &rightHand); //Get right hand.
    //MusicSequenceGetIndTrack(sequence, leftHandIndex, leftHand); //Get left hand.

    //Iterate through the right hand track and add user events.

    Boolean hasNextEvent = false;
    Boolean hasEvent = false;

    NewMusicEventIterator(rightHand, &iterator);
    MusicEventIteratorHasCurrentEvent(iterator, &hasEvent);
    MusicEventIteratorHasNextEvent(iterator, &hasNextEvent);

    while (hasNextEvent == true) {
        MusicTimeStamp timestamp = 0;
        MusicEventType eventType = 0;
        const void *eventData = NULL;
        int note;
        MusicTimeStamp duration;

        MusicEventIteratorGetEventInfo(iterator, &timestamp, &eventType, &eventData, NULL);

        if (eventType == kMusicEventType_MIDINoteMessage) {
            MIDINoteMessage *noteMessage = (MIDINoteMessage *)eventData;
            note = noteMessage->note;
            duration = noteMessage->duration;
            UserEvent event;

            event.length = 0;
            event.length = sizeof(UserEvent);
            event.playedNote = note;
            event.tStamp = timestamp;

            MusicEventUserData* data = (MusicEventUserData *)&event;
            MusicTrackNewUserEvent(rightHand, timestamp, data);
        }

        MusicEventIteratorHasNextEvent(iterator, &hasNextEvent);
        MusicEventIteratorNextEvent(iterator);
    }

    MusicSequenceSetUserCallback(sequence, noteUserCallback, NULL);

    MusicPlayerSetSequence(player, sequence);
    MusicPlayerPreroll(player);
}

- (void)viewDidUnload
{
    [self setPracticeWindowTitle:nil];
    [self setWhiteKey21:nil];
    // […]
    [self setWhiteKey108:nil];
    [self setBlackKey22:nil];
    // […]
    [self setBlackKey106:nil];
    [super viewDidUnload];
    // Release any retained subviews of the main view.
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return YES;
}

- (IBAction)practiceLesson:(id)sender {
    MusicPlayerStart(player);
}
@end

Answer 1

您与your other question走在了正确的轨道上。我不知道为什么你认为你需要一个完全不同的方法。

在回调中，请确保使用-performSelectorOnMainThread:或dispatch_async与dispatch_get_main_queue进行主线程上触摸UI的任何工作。可能任何使用PracticeViewController的代码都应该放在主线程上。

e.g。

void noteUserCallback (void *inClientData, MusicSequence inSequence, MusicTrack inTrack, MusicTimeStamp inEventTime, const MusicEventUserData *inEventData, MusicTimeStamp inStartSliceBeat, MusicTimeStamp inEndSliceBeat)
{   
    PracticeViewController* pvc = (__bridge PracticeViewController *)inClientData;

    dispatch_async(dispatch_get_main_queue(), ^{
        [pvc.whiteKey21 setImage:pvc.highlightA];
    });
    ...
}

如何在用户回调和视图之间进行通话？

1 个答案: