面试题：Objective-C的Core Haptics复杂触觉反馈设计

Question

假设你要为一款音乐应用设计独特的触觉反馈，根据不同的音符和节奏触发不同强度和时长的触觉反馈。请详细描述你将如何在Objective-C中利用Core Haptics技术来实现这一功能，包括数据结构的设计、反馈序列的规划等。

Answer 1

1. 引入Core Haptics框架

在项目的.h文件或.m文件开头引入Core Haptics框架：

#import <CoreHaptics/CoreHaptics.h>

2. 数据结构设计

• 音符结构体：用于表示单个音符及其对应的触觉反馈属性。

typedef struct {
    float intensity; // 触觉反馈强度，范围0.0 - 1.0
    float duration;  // 触觉反馈时长，单位秒
} NoteHaptic;

typedef struct {
    NoteHaptic notes[128]; // 假设最多支持128种不同音符
} MusicHapticData;

• 节奏结构体：用于表示节奏模式以及对应音符的触发顺序。

typedef struct {
    NSInteger noteIndices[100]; // 假设一个节奏最多100个音符
    NSInteger count;
} RhythmPattern;

3. 初始化Core Haptics引擎

在合适的地方，比如视图控制器的viewDidLoad方法中初始化Core Haptics引擎：

- (void)viewDidLoad {
    [super viewDidLoad];
    if (@available(iOS 13.0, *)) {
        CHHapticEngine *engine = [[CHHapticEngine alloc] initWithCallbackQueue:dispatch_get_main_queue()];
        NSError *error;
        if (![engine startAndReturnError:&error]) {
            NSLog(@"Error starting haptic engine: %@", error);
        }
        self.hapticEngine = engine;
    }
}

4. 规划反馈序列

• 根据音符创建触觉事件：

- (CHHapticEvent *)hapticEventForNoteIndex:(NSInteger)noteIndex withData:(MusicHapticData *)data {
    if (@available(iOS 13.0, *)) {
        NoteHaptic note = data->notes[noteIndex];
        CHHapticEventParameter *intensityParam = [[CHHapticEventParameter alloc] initWithParameterID:CHHapticEventParameterIDHapticIntensity value:note.intensity relative:NO];
        CHHapticEventParameter *durationParam = [[CHHapticEventParameter alloc] initWithParameterID:CHHapticEventParameterIDHapticDuration value:note.duration relative:NO];
        CHHapticEvent *event = [[CHHapticEvent alloc] initWithEventType:CHHapticEventTypeHapticContinuous parameters:@[intensityParam, durationParam] relativeTime:0];
        return event;
    }
    return nil;
}

• 根据节奏模式创建反馈序列：

- (CHHapticPattern *)hapticPatternForRhythm:(RhythmPattern *)rhythm withData:(MusicHapticData *)data {
    if (@available(iOS 13.0, *)) {
        NSMutableArray<CHHapticEvent *> *events = [NSMutableArray array];
        float timeOffset = 0;
        for (NSInteger i = 0; i < rhythm.count; i++) {
            NSInteger noteIndex = rhythm.noteIndices[i];
            CHHapticEvent *event = [self hapticEventForNoteIndex:noteIndex withData:data];
            event.relativeTime = timeOffset;
            [events addObject:event];
            timeOffset += data->notes[noteIndex].duration;
        }
        CHHapticPattern *pattern = [[CHHapticPattern alloc] initWithEvents:events error:nil];
        return pattern;
    }
    return nil;
}

5. 触发触觉反馈

当需要播放与音乐对应的触觉反馈时，执行以下操作：

- (void)playHapticForRhythm:(RhythmPattern *)rhythm withData:(MusicHapticData *)data {
    if (@available(iOS 13.0, *)) {
        CHHapticPattern *pattern = [self hapticPatternForRhythm:rhythm withData:data];
        CHHapticPatternPlayer *player = [self.hapticEngine makePlayerWithPattern:pattern error:nil];
        [player startAtTime:0 error:nil];
    }
}

6. 清理资源

在适当的时候，比如视图控制器销毁时，停止并关闭Core Haptics引擎：

- (void)dealloc {
    if (@available(iOS 13.0, *)) {
        [self.hapticEngine stopAndReturnError:nil];
        [self.hapticEngine close];
    }
}