ios – 在Swift 3中提取Data对象的片段

let myDataStream = Data(bytes: [24,163,209,194,255,1,184,230,37,208,140,201,6,64,7,98,108,117,...])

let streamLength = Int(myDataStream[0])
let newStream = Data(bytes: myDataStream[0...streamLength])

您可以结合使用subdata和removeSubRange方法来获得所需的结果.

subData(in :)是Data结构上的实例方法.

removeSubRange()也是Data结构上的实例方法.

您可以在此处阅读有关这些方法的更多信息：https://developer.apple.com/reference/foundation/data

示例方法：

func extract(from data: inout Data) -> Data? {
    guard data.count > 0 else {
        return nil
    }

    // Define the length of data to return
    let length = Int.init(data[0])

    // Create a range based on the length of data to return
    let range = Range(0..<length)

    // Get a new copy of data
    let subData = data.subdata(in: rangE)

    // Mutate data
    data.removeSubrange(rangE)

    // Return the new copy of data
    return subData
}

用法：

// Data (27 bytes)
var data = Data(bytes: [24,42,63,78,200,3,34,36])

// First extraction
let first = extract(from: &data)
print(first!) // Prints 24 bytes
print(data) // Prints 3 bytes

// Second extraction
let second = extract(from: &data)
print(second!) // Prints 3 bytes
print(data) // Prints 0 bytes

// Third extraction
let third = extract(from: &data)
print(third ?? "No Data") // Prints "No Data"

进行扩展

您还可以将上面的提取方法包装在Data的扩展中,如下所示：

extension Data {
    mutaTing func extract() -> Data? {
        guard self.count > 0 else {
            return nil
        }

        // Define the length of data to return
        let length = Int.init(self[0])

        // Create a range based on the length of data to return
        let range = Range(0..<length)

        // Get a new copy of data
        let subData = self.subdata(in: rangE)

        // Mutate data
        self.removeSubrange(rangE)

        // Return the new copy of data
        return subData
    }
}

然后你可以使用这样的方法：

// Data (27 bytes)
var data = Data(bytes: [24,36])

// First extraction
let first = data.extract()
print(first!) // Prints 24 bytes
print(data) // Prints 3 bytes

// Second extraction
let second = data.extract()
print(second!) // Prints 3 bytes
print(data) // Prints 0 bytes

// Third extraction
let third = data.extract()
print(third ?? "No Data") // Prints "No Data"