如何在目标c下面写下代码？

Question

我将代码从swift转换为客观c：

func toPCMBuffer(data: NSData) -> AVAudioPCMBuffer {
        let audioFormat = AVAudioFormat(commonFormat: AVAudioCommonFormat.pcmFormatFloat32, sampleRate: 8000, channels: 1, interleaved: false)  // given NSData audio format
        let PCMBuffer = AVAudioPCMBuffer(pcmFormat: audioFormat, frameCapacity: UInt32(data.length) / audioFormat.streamDescription.pointee.mBytesPerFrame)
        PCMBuffer.frameLength = PCMBuffer.frameCapacity
        let channels = UnsafeBufferPointer(start: PCMBuffer.floatChannelData, count: Int(PCMBuffer.format.channelCount))
        data.getBytes(UnsafeMutableRawPointer(channels[0]) , length: data.length)
        return PCMBuffer
    }

我转换为目标c：

-(AVAudioPCMBuffer*)toPCMBuffer: (NSData*)data {

    AVAudioFormat * audioFormat = [[AVAudioFormat alloc]initWithCommonFormat:AVAudioPCMFormatFloat32 sampleRate:8000 channels:1 interleaved:false];
    AVAudioPCMBuffer* PCMBuffer = [[AVAudioPCMBuffer alloc]initWithPCMFormat:audioFormat frameCapacity:data.length/audioFormat.streamDescription->mBytesPerFrame];
    PCMBuffer.frameLength = PCMBuffer.frameCapacity;
    float *channels = malloc(PCMBuffer.format.channelCount * sizeof(float)); // remember to free eventually
    memcpy(channels, PCMBuffer.floatChannelData, PCMBuffer.format.channelCount * sizeof(float));
    [data getBytes:channels length:data.length];
    return PCMBuffer;

}

但我不确定纠正行代码：

AVAudioPCMBuffer* PCMBuffer = [[AVAudioPCMBuffer alloc]initWithPCMFormat:audioFormat frameCapacity:data.length/audioFormat.streamDescription->mBytesPerFrame];

这是我不知道如何写UInt32(data.length)到目标c的代码

和：

如何将UnsafeMutableRawPointer(channels[0])转换为objc？

[data getBytes:channels length:data.length];