不能UnsafeMutableRawPointer的值轉換爲BluetoothDeviceAddress

Question

我想轉換此源代碼：

BluetoothDeviceAddress *deviceAddress = malloc(sizeof(BluetoothDeviceAddress)); 

斯威夫特，這給了我：

let deviceAddress: BluetoothDeviceAddress = malloc(sizeof(BluetoothDeviceAddress)) 

但是，我發現，在斯威夫特3/4，sizeof不再使用，但這不是我的錯誤，Xcode返回：

「無法轉換'UnsafeMutableRawPointer！'類型的值到指定類型「BluetoothDeviceAddress」「

我試圖更改爲malloc(MemoryLayout<BluetoothDeviceAddress>.size)但仍然是相同的錯誤。

編輯： 作爲由MartinR的意見建議，我試圖改變到let deviceAddress = BluetoothDeviceAddress() 但後來當我想初始化IOBluetoothDevice，我還得到一個錯誤（selectedDevice是IOBluetoothDevice一個VAR）：

self.selectedDevice = IOBluetoothDevice(address: deviceAddress) 

錯誤：無法將類型'BluetoothDeviceAddress'的值轉換爲期望的參數類型'UnsafePointer！'

最佳，

安東尼

Answer 1

要回答你直接的問題：從原始 指針獲取類型的指針斯威夫特被稱爲「綁定」並完成與bindMemory()：

let ptr = malloc(MemoryLayout<BluetoothDeviceAddress>.size)! // Assuming that the allocation does not fail 
let deviceAddressPtr = ptr.bindMemory(to: BluetoothDeviceAddress.self, capacity: 1) 
deviceAddressPtr.initialize(to: BluetoothDeviceAddress()) 
// Use deviceAddressPtr.pointee to access pointed-to memory ... 

let selectedDevice = IOBluetoothDevice(address: deviceAddressPtr) 
// ... 

deviceAddressPtr.deinitialize(count: 1) 
free(ptr) 

相反的malloc/free，可以使用Swift中的Unsafe(Mutable)Pointer的分配/釋放方法 ：

let deviceAddressPtr = UnsafeMutablePointer<BluetoothDeviceAddress>.allocate(capacity: 1) 
deviceAddressPtr.initialize(to: BluetoothDeviceAddress()) 
// Use deviceAddressPtr.pointee to access pointed-to memory ... 

let selectedDevice = IOBluetoothDevice(address: deviceAddressPtr) 
// ... 

deviceAddressPtr.deinitialize(count: 1) 
deviceAddressPtr.deallocate(capacity: 1) 

有關原始指針和綁定的更多信息，請參閱SE-0107 UnsafeRawPointer API 。

然而，它通常更容易創建該類型直接 的值並傳遞作爲INOUT表達與&。例如：

var deviceAddress = BluetoothDeviceAddress() 
// ... 

let selectedDevice = IOBluetoothDevice(address: &deviceAddress) 
// ...