Swift Inbox

• Swfit Inbox

  • pending

    • @EnvironmentObject & environmentObject(_:)

  • Swift 中含关联值的枚举

  • Error

    • Overview

    • Using Enumerations as Errors

    • Including More Data in Errors

  • JSONEncoder

pending

• some , Swift 5.1

• @frozen

• Combine

  • Self.Output

• SwiftUI

@EnvironmentObject & environmentObject(_:)

• The @EnvironmentObject attribute.

  • You use this attribute in views that are lower down in the view hierarchy to receive data from views that are higher up.

• The environmentObject(_:) modifier.

  • You apply this modifier so that views further down in the view hierarchy can read data objects passed down through the environment.

Swift 中含关联值的枚举

Swift 中含关联值的枚举

• static 可以修饰存储属性，而 class 不能；

• class 修饰的方法可以继承，而 static 不能。

• 在协议中需用 static 来修饰。

Error

Swift Docs: Protocol-Error

Declaration：

public protocol Error : Sendable {
}

Overview

Any type that declares conformance to the Error protocol can be used to represent an error in Swift’s error handling system. Because the Error protocol has no requirements of its own, you can declare conformance on any custom type you create.

Using Enumerations as Errors

Swift’s enumerations are well suited to represent simple errors.

enum IntParsingError: Error {
    case overflow
    case invalidInput(Character)
}

extension Int {
    init(validating input: String) throws {
        // ...
        let c = _nextCharacter(from: input)
        if !_isValid(c) {
            throw IntParsingError.invalidInput(c)
        }
        // ...
    }
}

do {
    let price = try Int(validating: "$100")
} catch IntParsingError.invalidInput(let invalid) {
    print("Invalid character: '\(invalid)'")
} catch IntParsingError.overflow {
    print("Overflow error")
} catch {
    print("Other error")
}
// Prints "Invalid character: '$'"

Including More Data in Errors

Sometimes you may want different error states to include the same common data, such as the position in a file or some of your application’s state. When you do, use a structure to represent errors. The following example uses a structure to represent an error when parsing an XML document, including the line and column numbers where the error occurred:

struct XMLParsingError: Error {
    enum ErrorKind {
        case invalidCharacter
        case mismatchedTag
        case internalError
    }

    let line: Int
    let column: Int
    let kind: ErrorKind
}

func parse(_ source: String) throws -> XMLDoc {
    // ...
    throw XMLParsingError(line: 19, column: 5, kind: .mismatchedTag)
    // ...
}

do {
    let xmlDoc = try parse(myXMLData)
} catch let e as XMLParsingError {
    print("Parsing error: \(e.kind) [\(e.line):\(e.column)]")
} catch {
    print("Other error: \(error)")
}
// Prints "Parsing error: mismatchedTag [19:5]"

JSONEncoder

An object that encodes instances of a data type as JSON objects.

class JSONEncoder

struct GroceryProduct: Codable {
    var name: String
    var points: Int
    var description: String?
}

let pear = GroceryProduct(name: "Pear", points: 250, description: "A ripe pear.")

let encoder = JSONEncoder()
encoder.outputFormatting = .prettyPrinted

let data = try encoder.encode(pear)
print(String(data: data, encoding: .utf8)!)

/* Prints:
 {
   "name" : "Pear",
   "points" : 250,
   "description" : "A ripe pear."
 }
*/