swift3中的UnsafeMutablePointer错误答案

【问题标题】：Error in UnsafeMutablePointer in swift3swift3中的UnsafeMutablePointer错误
【发布时间】：2016-11-15 08:56:55
【问题描述】：

我的鳕鱼是这样的

let samples = UnsafeMutableBufferPointer<Int16>(start:UnsafeMutablePointer(buffer.mData), count: Int(buffer.mDataByteSize)/sizeof(Int16))

运行此代码时出现以下错误

Cannot invoke initializer for type 'UnsafeMutablePointer<_>' with an argument list of type '(UnsafeMutableRawPointer?)'

buffer.mdata 有原始数据。我该如何解决这个问题。提前致谢

【问题讨论】：

您可以编辑问题以显示mData 声明吗？

标签： swift swift3 unsafe-pointers

【解决方案1】：

假设buffer 是来自AVFoundation 的AudioBuffer 框架：buffer.mData 是一个“可选的原始指针” UnsafeMutableRawPointer?，在 Swift 3 中你必须绑定指向类型化指针的原始指针：

let buffer: AudioBuffer = ...

if let mData = buffer.mData {
    let numSamples = Int(buffer.mDataByteSize)/MemoryLayout<Int16>.size
    let samples = UnsafeMutableBufferPointer(start: mData.bindMemory(to: Int16.self, capacity: numSamples),
                                             count: numSamples)
    // ...
}

见SE-0107 UnsafeRawPointer API 有关原始指针的更多信息。

【讨论】：

【解决方案2】：

根据文档：

// Creates an UnsafeMutablePointer over the count contiguous Element instances beginning at start.
init(start: UnsafeMutablePointer<Element>?, count: Int)

所以

let samples = UnsafeMutableBufferPointer<Int16>(start:UnsafeMutablePointer(buffer.mData), count: Int(buffer.mDataByteSize)/sizeof(Int16))

会是这样的：

let byteSize = Int16(buffer.mDataByteSize)/sizeOf(Int16)
let buffer:UnsafeMutablePointer<Int16> = buffer.mData.assumingMemoryBound(to: Int16.self)
let samples = UnsafeMutableBufferPointer<Int16>(start:buffer, count:byteSize)

有多种方法可以将UnsafeMutableRawPointer 转换为UnsafeMutablePointer<T>。 Martin 在上面的答案中已经给出了一个转换，另一个在这个例子中。

【讨论】：