NSData与NSValue?如何在sendMIDISysExEvent:(NSData*)midiData中封装C结构

我在试着找出使用的方法 sendMIDISysExEvent:(NSData *)midiData 作为在音乐应用程序中重新调谐少数MIDI音符的一种方式。我想要 ViewController Synth 类更改10个音符的调谐。用于重新调谐一个音符的标准MIDI系统专用消息格式如下所示

                 F0 7F <device ID> 08 02 tt ll [kk xx yy zz] F7.

legend: tt ll [kk xx yy zz] (注意:与MIDI 1.0详细规范4.2第49页略有不同)

具有 typedef struct float uint8_t 表示调谐频率,例如。

    typedef struct
    {
    uint8_t SYSEX_SysexHeader;                // oxF0h;     // System Exclusive Header
    uint8_t SYSEX_UniversalRealTimeHeader;    // ox7Fh;     // Universal RealTime Header
    uint8_t SYSEX_myPhone;                    // ox00h;     // ID of target device (e.g. iPhone)
    uint8_t SYSEX_subID1;                     // ox08h;     // sub-ID #1 (MIDI Tuning Standard)
    uint8_t SYSEX_subID2;                     // ox02h;     // sub-ID #2 (note change)
    uint8_t SYSEX_tuningProgramNumber;        // ox0h;      // tuning program number (0 -127)
    uint8_t SYSEX_numberOfKeys;               // ox10h;     // number of changes

    uint8_t SYSEX_key0;
    float   TUNING_pitch_0;

    uint8_t SYSEX_key1;
    float   TUNING_pitch_1;

    uint8_t SYSEX_key2;
    float   TUNING_pitch_2;

    uint8_t SYSEX_key3;
    float   TUNING_pitch_3;

    uint8_t SYSEX_key4;
    float   TUNING_pitch_4;

    uint8_t SYSEX_key5;
    float   TUNING_pitch_5;

    uint8_t SYSEX_key6;
    float   TUNING_pitch_6;

    uint8_t SYSEX_key7;
    float   TUNING_pitch_7;

    uint8_t SYSEX_key8;
    float   TUNING_pitch_8;

    uint8_t SYSEX_key9;
    float   TUNING_pitch_9;

    uint8_t eox;                                // OxF7h;       //

    }
    TuneEvent;

仍然在h

    typedef NS_ENUM(NSInteger, SYSEX)
    {
    SYSEX_SysexHeader               = 240,
    SYSEX_UniversalRealTimeHeader   = 127,
    SYSEX_myPhone                   = 0,
    SYSEX_subID1                    = 8,
    SYSEX_subID2                    = 2,
    SYSEX_tuningProgramNumber       = 0,
    SYSEX_numberOfKeysToBeChanged   = 1,
    SYSEX_key0                      = 61,
    SYSEX_key1                      = 62,
    SYSEX_key2                      = 63,
    SYSEX_key3                      = 64,
    SYSEX_key4                      = 65,
    SYSEX_key5                      = 66,
    SYSEX_key6                      = 67,
    SYSEX_key7                      = 68,
    SYSEX_key8                      = 69,
    SYSEX_key9                      = 70,
    SYSEX_eox                       = 247
    };

    typedef NS_ENUM(NSInteger, TUNING)
    {
    TUNING_pitch0,
    TUNING_pitch1,
    TUNING_pitch2,
    TUNING_pitch3,
    TUNING_pitch4,
    TUNING_pitch5,
    TUNING_pitch6,
    TUNING_pitch7,
    TUNING_pitch8,
    TUNING_pitch9
    };

    float TUNING_float(TUNING micro);

最后,对于浮点值。。。 (thanks to this answer)

PlayViewController.m

    float TUNING_float(TUNING micro) 
    {
    switch (micro) 
        {
        case TUNING_pitch0:
            return  579.4618f;
        case TUNING_pitch1:
            return  607.0552f;
        case TUNING_pitch2:
            return  662.2421f;
        case TUNING_pitch3:
            return  708.2311f;
        case TUNING_pitch4:
            return  772.6157f;
        case TUNING_pitch5:
            return  809.4070f;
        case TUNING_pitch6:
            return  882.9894f;
        case TUNING_pitch7:
            return  910.5828f;
        case TUNING_pitch8:
            return  993.3631f;
        case TUNING_pitch9:
            return  1030.1540f;
        default:
            return   0.0f;
        }
    }

this answer 我开始问我如何根据 NSData sendMIDISysExEvent:(NSData*)midiData 将发送。和 this answer NSValue 这是封装C结构的更好方法,就像我试图创建的那样,所以我很困惑。如果真是这样,我很奇怪为什么苹果会推出这样的方法 sendMIDISysExEvent:(NSData *)midiData .

我的问题是:基于消息格式 (在我上面的代码中概述) ,我该如何准备 midiData 为了用这种方法发送?

字节数 数据类型 操作文件数据 和 NSValue公司 。这也意味着 仅设计用于处理字节数据,即。 uint8\u t 而不是 float. 换言之,明智的选择是根据以下MIDI调谐标准的摘录,使用字节表示频率值

    yy = MSB of fractional part (1/128 semitone = 100/128 cents = .78125 cent units)
    zz = LSB of fractional part (1/16384 semitone = 100/16384 cents = .0061 cent units)