如何在用戶回調和視圖之間進行通話？

Question

我想知道如何基於用戶事件在MIDI播放過程中傳遞時調用的用戶事件回調的內容來更新UI元素（UIImageViews）。更具體地說，這些用戶事件包含傳遞到用戶回調函數中的音符數據（例如播放的音符是60，又名中間C）。

我想基於播放的音符更新我的UIImageViews。我試圖從回調中訪問UIImageViews，但由於它沒有對ViewController的直接訪問，並且因爲它運行在主線程以外的線程上，所以我被建議採用不同的方式。

所以，我想要做的是創建一個單獨的控制器，可以將回調函數的信息傳遞給UI，但我不知道該怎麼做。我已經在下面發佈了我的ViewController的代碼。它包含回調函數以及用於設置用戶事件和其他視圖相關內容的所有相關代碼。

我正在使用iOS 5在Xcode 4.3.1中工作，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

你是正確的軌道上your other question。我不知道你爲什麼認爲你需要一個完全不同的方法。

在您的回調中，請務必使用-performSelectorOnMainThread:或dispatch_async和dispatch_get_main_queue來執行任何涉及主線程UI的工作。可能的話，任何使用PracticeViewController的代碼都應該放在主線程中。

例如

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]; 
    }); 
    ... 
}