xcode 来自 UInt8 的 NSData
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NSData from UInt8
提问by Ondrej Rafaj
I have recently found a source code in swift and I am trying to get it to objective-C. The one thing I was unable to understand is this:
我最近在 swift 中找到了一个源代码，我正在尝试将其转换为 Objective-C。我无法理解的一件事是：
var theData:UInt8!
theData = 3;
NSData(bytes: [theData] as [UInt8], length: 1)
Can anybody help me with the Obj-C equivalent?
任何人都可以帮助我使用 Obj-C 等效项吗？
Just to give you some context, I need to send UInt8 to a CoreBluetooth peripheral (CBPeripheral) as UInt8. Float or integer won't work because the data type would be too big.
只是为了给你一些上下文，我需要将 UInt8 作为 UInt8 发送到 CoreBluetooth 外围设备 (CBPeripheral)。浮点数或整数将不起作用，因为数据类型太大。
回答by Martin R
If you write the Swift code slightly simpler as
如果你写的 Swift 代码稍微简单一点
var theData : UInt8 = 3
let data = NSData(bytes: &theData, length: 1)
then it is relatively straight-forward to translate that to Objective-C:
那么将其转换为 Objective-C 相对简单：
uint8_t theData = 3;
NSData *data = [NSData dataWithBytes:&theData length:1];
For multiple bytes you would use an array
对于多个字节，您将使用数组
var theData : [UInt8] = [ 3, 4, 5 ]
let data = NSData(bytes: &theData, length: theData.count)
which translates to Objective-C as
转换为 Objective-C 为
uint8_t theData[] = { 3, 4, 5 };
NSData *data = [NSData dataWithBytes:&theData length:sizeof(theData)];
(and you can omit the address-of operator in the last statement, see for example How come an array's address is equal to its value in C?).
（并且您可以在最后一条语句中省略 address-of 运算符，例如参见数组的地址如何等于其在 C 中的值？）。
回答by YannSteph
In Swift 3
在斯威夫特 3
var myValue: UInt8 = 3 // This can't be let properties
let value = Data(bytes: &myValue, count: MemoryLayout<UInt8>.size)
回答by AechoLiu
In Swift,
在斯威夫特，
Datahas a native initmethod.
Data有一个本地init方法。
// Foundation -> Data
/// Creates a new instance of a collection containing the elements of a
/// sequence.
///
/// - Parameter elements: The sequence of elements for the new collection.
/// `elements` must be finite.
@inlinable public init<S>(_ elements: S) where S : Sequence, S.Element == UInt8
@available(swift 4.2)
@available(swift, deprecated: 5, message: "use `init(_:)` instead")
public init<S>(bytes elements: S) where S : Sequence, S.Element == UInt8
So, the following will work.
因此，以下将起作用。
let values: [UInt8] = [1, 2, 3, 4]
let data = Data(values)
