我一直致力于掌握 AUAudioUnits 背后的理念,并在 presentation video 中给出的 Xcode 中写下示例代码来自介绍该主题的 Apple 的 WWDC 2016。事实证明,这段代码是为 Swift 2 编写的,而 Swift 3 引入了一种新的指针处理方式(如 here 和 here 所示)。现在我对使用 Swift 编程还很陌生,不熟悉它的一些概念,而且我不知道如何手动执行从 Swift 2 到 Swift 3 的转换。即使使用build设置
Use Legacy Swift Language Version = yes
我无法让它运行。
这是 Swift 2 的代码,与视频中的代码完全相同:
import Foundation
import AVFoundation
class SquareWaveGenerator {
let sampleRate: Double
let frequency: Double
let amplitude: Float
var counter: Double = 0.0
init(sampleRate: Double, frequency: Double, amplitude: Float) {
self.sampleRate = sampleRate
self.frequency = frequency
self.amplitude = amplitude
}
func render(buffer: AudioBuffer) {
let nframes = Int(buffer.mDataByteSize) / sizeof(Float)
var ptr = UnsafeMutablePointer<Float>(buffer.mData)
var j = self.counter
let cycleLength = self.sampleRate / self.frequency
let halfCycleLength = cycleLength / 2
let amp = self.amplitude, minusAmp = -amp
for _ in 0..<nframes {
if j < halfCycleLength {
ptr.pointee = amp
} else {
ptr.pointee = minusAmp
}
ptr = ptr.successor()
j += 1.0
if (j > cycleLength) {
j -= cycleLength
}
}
self.counter = j
}
}
func main() {
//Create an AudioComponentDescription for the input/output unit we want to use.
#if os(iOS)
let kOutputUnitSubType = kAudioUnitSubType_RemoteIO
#else
let kOutputUnitSubType = kAudioUnitSubType_HALOutput
#endif
let ioUnitDesc = AudioComponentDescription(
componentType: kAudioUnitType_Output,
componentSubType: kOutputUnitSubType,
componentManufacturer: kAudioUnitManufacturer_Apple,
componentFlags: 0,
componentFlagsMask: 0)
let ioUnit = try! AUAudioUnit(componentDescription: ioUnitDesc, options: AudioComponentInstantiationOptions())
/*
Set things up to render at the same sample rate as the hardware,
up to 2 channels. Note that the hardware format may not be a standard
format, so we make a separate render format with the same sample rate
and the desired channel count.
*/
let hardwareFormat = ioUnit.outputBusses[0].format
let renderFormat = AVAudioFormat(standardFormatWithSampleRate: hardwareFormat.sampleRate, channels: min(2,hardwareFormat.channelCount))
try! ioUnit.inputBusses[0].setFormat(renderFormat)
// Create square wave generators.
let generatorLeft = SquareWaveGenerator(sampleRate: renderFormat.sampleRate, frequency: 440.0, amplitude: 0.1)
let generatorRight = SquareWaveGenerator(sampleRate: renderFormat.sampleRate, frequency: 440.0, amplitude: 0.1)
// Install a block which will be called to render.
ioUnit.outputProvider = { (actionFlags: UnsafeMutablePointer<AudioUnitRenderActionFlags>, timestamp: UnsafePointer<AudioTimeStamp>, frameCount: AUAudioFrameCount, busIndex: Int, rawBufferList: UnsafeMutablePointer<AudioBufferList>) -> AUAudioUnitStatus in
let bufferList = UnsafeMutableAudioBufferListPointer(rawBufferList)
if bufferList.count > 0 {
generatorLeft.render(bufferList[0])
if bufferList.count > 1 {
generatorRight.render(bufferList[1])
}
}
return noErr
}
// Allocate render resources, then start the audio hardware.
try! ioUnit.allocateRenderResources()
try! ioUnit.startHardware()
sleep(3)
ioUnit.stopHardware()
}
main()
这段代码:
ptr.pointee = amp
[...]
ptr.pointee = minusAmp
抛出以下错误:
Value of type 'UnsafeMutablePointer' has no member 'pointee'
由于无法手动解决这个问题,我尝试手动将代码转换为 Swift 3,希望问题能得到解决。在这里:
import Foundation
import AVFoundation
class SquareWaveGenerator {
let sampleRate: Double
let frequency: Double
let amplitude: Float
var counter: Double = 0.0
init(sampleRate: Double, frequency: Double, amplitude: Float) {
self.sampleRate = sampleRate
self.frequency = frequency
self.amplitude = amplitude
}
func render(buffer: AudioBuffer) {
let nframes = Int(buffer.mDataByteSize) / MemoryLayout<Float>.size
var ptr = buffer.mData
var j = self.counter
let cycleLength = self.sampleRate / self.frequency
let halfCycleLength = cycleLength / 2
let amp = self.amplitude, minusAmp = -amp
for _ in 0..<nframes {
if j < halfCycleLength {
ptr?.pointee = amp
} else {
ptr?.pointee = minusAmp
}
ptr = ptr?.advanced(by: 1)
j += 1.0
if (j > cycleLength) {
j -= cycleLength
}
}
self.counter = j
}
}
func main() {
//Create an AudioComponentDescription for the input/output unit we want to use.
#if os(iOS)
let kOutputUnitSubType = kAudioUnitSubType_RemoteIO
#else
let kOutputUnitSubType = kAudioUnitSubType_HALOutput
#endif
let ioUnitDesc = AudioComponentDescription(
componentType: kAudioUnitType_Output,
componentSubType: kOutputUnitSubType,
componentManufacturer: kAudioUnitManufacturer_Apple,
componentFlags: 0,
componentFlagsMask: 0)
let ioUnit = try! AUAudioUnit(componentDescription: ioUnitDesc, options: AudioComponentInstantiationOptions())
/*
Set things up to render at the same sample rate as the hardware,
up to 2 channels. Note that the hardware format may not be a standard
format, so we make a separate render format with the same sample rate
and the desired channel count.
*/
let hardwareFormat = ioUnit.outputBusses[0].format
let renderFormat = AVAudioFormat(standardFormatWithSampleRate: hardwareFormat.sampleRate, channels: min(2,hardwareFormat.channelCount))
try! ioUnit.inputBusses[0].setFormat(renderFormat)
// Create square wave generators.
let generatorLeft = SquareWaveGenerator(sampleRate: renderFormat.sampleRate, frequency: 440.0, amplitude: 0.1)
let generatorRight = SquareWaveGenerator(sampleRate: renderFormat.sampleRate, frequency: 440.0, amplitude: 0.1)
// Install a block which will be called to render.
ioUnit.outputProvider = { (actionFlags: UnsafeMutablePointer<AudioUnitRenderActionFlags>, timestamp: UnsafePointer<AudioTimeStamp>, frameCount: AUAudioFrameCount, busIndex: Int, rawBufferList: UnsafeMutablePointer<AudioBufferList>) -> AUAudioUnitStatus in
let bufferList = UnsafeMutableAudioBufferListPointer(rawBufferList)
if bufferList.count > 0 {
generatorLeft.render(buffer: bufferList[0])
if bufferList.count > 1 {
generatorRight.render(buffer: bufferList[1])
}
}
return noErr
}
// Allocate render resources, then start the audio hardware.
try! ioUnit.allocateRenderResources()
try! ioUnit.startHardware()
sleep(3)
ioUnit.stopHardware()
}
main()
我在哪里再次遇到上述错误
Value of type 'UnsafeMutablePointer' has no member 'pointee'
最后,我想到了类似的东西
ptr?.storeBytes(of: T, as: T.Type)
应该能够取代“pointee”结构。如果我理解正确的话,“T”是我想存储在指针位置的值。就我而言,那将是“放大器”。 “amp”是 Float 类型。
但是无论我做什么,我都无法让代码运行。它只是不会接受任何类似的东西
ptr?.storeBytes(of: amp, as: Float())
throw
Cannot convert value of type 'Float' to expected argument type 'T.Type'
或
ptr?.storeBytes(of: amp, as: Float.self)
不再立即抛出错误并正确编译,但在运行时,收到 lldb 错误消息
fatal error: storeBytes to misaligned raw pointer
本质上,我不知道自己在做什么,不理解这种情况下“T.Type”的概念,我被困住了。所以我有两个问题:
1) How do I solve this issue and get the code running?
2) Where can I learn more about these types of constructions à la Type which will help me understand what they are and what they mean?
最佳答案
你在这里遇到的是 while AudioBuffer.mData
曾经是 UnsafeMutablePointer
, 它现在是 UnsafeMutableRawPointer
,这是 Swift 3 中的新功能。要像以前一样处理该数据,您可以将引用的内存绑定(bind)到 Float
。类型,像这样:
guard let mData = buffer.mData
else { return /* or error */ }
let nframes = Int(buffer.mDataByteSize) / MemoryLayout<Float>.size
var ptr = mData.bindMemory(to: Float.self, capacity: nframes)
现在ptr
是一个 UnsafeMutablePointer<Float>
,这是您之前使用的,您应该能够访问它的 pointee
属性(property)没有问题。
注意:每当您看到 T.Type
在函数声明中,它要求类型本身,而不是类型的实例。在这种情况下,您要传递 Float
的类型,即 Float.self
.打电话Float()
,另一方面,创建一个新的 Float
实例。
最后,不再继续直接使用 ptr
,我会创建一个缓冲区,它至少会为您提供 Debug模式下的边界检查和更好的界面:
let buffer = UnsafeMutableBufferPointer<Float>(start: ptr, count: frames)
// ...
for i in 0..<nframes {
if j < halfCycleLength {
buffer[i] = amp
} else {
buffer[i] = minusAmp
}
j += 1.0
// ...
}
关于swift - 在将 Swift 2 转换为 Swift 3 期间寻找 "pointee"的替代品时出现问题,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/41308790/