extension URLRequest {
public init(url: URLConvertible, method: HTTPMethod, headers: HTTPHeaders? = nil) throws {
let url = try url.asURL()
self.init(url: url)
httpMethod = method.rawValue
if let headers = headers {
for (headerField, headerValue) in headers {
setValue(headerValue, forHTTPHeaderField: headerField)
}
}
}
func adapt(using adapter: RequestAdapter?) throws -> URLRequest {
guard let adapter = adapter else { return self }
return try adapter.adapt(self)
}
}
url是继承了URLConvertible协议的类型
method是HTTPMethod枚举类型
public enum HTTPMethod: String {
case get = "GET"
case head = "HEAD"
case post = "POST"
...
}
headers是HTTPHeaders类型，其实就是通过类型重命名typealias关键字，将key－value都为String类型的字典重命名为HTTPHeaders
//A dictionary of headers to apply to a
URLRequest.
public typealias HTTPHeaders = [String: String]
并且可以看出，url和method都是必须要有的，headers是可选的
let url = try url.asURL()
这里用try，是因为asURL()定义在类型转换时出现错误throws异常
self.init(url: url)
这里调用URLRequest的初始化方法
//Creates and initializes a URLRequest with the given URL and cache policy.
public init ( url: URL, cachePolicy: URLRequest.CachePolicy = default, timeoutInterval: TimeInterval = default )
这里的CachePolicy其实是NSURLRequest，默认是：.useProtocolCachePolicy
public typealias CachePolicy = NSURLRequest.CachePolicy
httpMethod = method.rawValue
举个官方的🌰，貌似挺好理解
enum PaperSize: String {
case A4, A5, Letter, Legal
}
let selectedSize = PaperSize.Letter
print(selectedSize.rawValue)
// Prints "Letter"
print(selectedSize == PaperSize(rawValue: selectedSize.rawValue)!)
// Prints "true"
if let headers = headers {
for (headerField, headerValue) in headers {
setValue(headerValue, forHTTPHeaderField: headerField)
}
}
for循环的这种方式是由于headers是元组类型
当看到using adapter: RequestAdapter?的时候，我已经知道这是个协议了，而且有throws，说明我们在return的时候需要try。
使用guard来判断是否有值，比if更加清晰
public protocol RequestAdapter {
func adapt(_ urlRequest: URLRequest) throws -> URLRequest
}
