"Publishing changes from background threads is not allowed" 使用 URLSession 获取数据时
"Publishing changes from background threads is not allowed" while fetching data using URLSession
我正在尝试从 Unsplash API 获取数据，但是我收到以下错误：“不允许从后台线程发布更改；确保从主线程发布值（通过像这样的运算符在模型更新时接收（on :)）。
这是模型结构：
// MARK: - UnsplashData
struct UnsplashData: Codable {
let id: String
let createdAt, updatedAt, promotedAt: Date
let width, height: Int
let color, blurHash: String
let unsplashDataDescription: String?
let altDescription: String
let urls: Urls
let links: UnsplashDataLinks
let categories: [String]
let likes: Int
let likedByUser: Bool
let currentUserCollections: [String]
let sponsorship: JSONNull?
let user: User
let exif: Exif
let location: Location
let views, downloads: Int
enum CodingKeys: String, CodingKey {
case id
case createdAt = "created_at"
case updatedAt = "updated_at"
case promotedAt = "promoted_at"
case width, height, color
case blurHash = "blur_hash"
case unsplashDataDescription = "description"
case altDescription = "alt_description"
case urls, links, categories, likes
case likedByUser = "liked_by_user"
case currentUserCollections = "current_user_collections"
case sponsorship, user, exif, location, views, downloads
}
}
// MARK: - Exif
struct Exif: Codable {
let make, model, exposureTime, aperture: String
let focalLength: String
let iso: Int
enum CodingKeys: String, CodingKey {
case make, model
case exposureTime = "exposure_time"
case aperture
case focalLength = "focal_length"
case iso
}
}
// MARK: - UnsplashDataLinks
struct UnsplashDataLinks: Codable {
let linksSelf, html, download, downloadLocation: String
enum CodingKeys: String, CodingKey {
case linksSelf = "self"
case html, download
case downloadLocation = "download_location"
}
}
// MARK: - Location
struct Location: Codable {
let title, name, city, country: String?
let position: Position
}
// MARK: - Position
struct Position: Codable {
let latitude, longitude: Double?
}
// MARK: - Urls
struct Urls: Codable {
let raw, full, regular, small: String
let thumb: String
}
// MARK: - User
struct User: Codable {
let id: String
let updatedAt: Date
let username, name, firstName, lastName: String
let twitterUsername: String?
let portfolioURL: String
let bio: String?
let location: String
let links: UserLinks
let profileImage: ProfileImage
let instagramUsername: String
let totalCollections, totalLikes, totalPhotos: Int
let acceptedTos: Bool
enum CodingKeys: String, CodingKey {
case id
case updatedAt = "updated_at"
case username, name
case firstName = "first_name"
case lastName = "last_name"
case twitterUsername = "twitter_username"
case portfolioURL = "portfolio_url"
case bio, location, links
case profileImage = "profile_image"
case instagramUsername = "instagram_username"
case totalCollections = "total_collections"
case totalLikes = "total_likes"
case totalPhotos = "total_photos"
case acceptedTos = "accepted_tos"
}
}
// MARK: - UserLinks
struct UserLinks: Codable {
let linksSelf, html, photos, likes: String
let portfolio, following, followers: String
enum CodingKeys: String, CodingKey {
case linksSelf = "self"
case html, photos, likes, portfolio, following, followers
}
}
// MARK: - ProfileImage
struct ProfileImage: Codable {
let small, medium, large: String
}
// MARK: - Encode/decode helpers
class JSONNull: Codable, Hashable {
public static func == (lhs: JSONNull, rhs: JSONNull) -> Bool {
return true
}
public var hashValue: Int {
return 0
}
public func hash(into hasher: inout Hasher) {
// No-op
}
public init() {}
public required init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
if !container.decodeNil() {
throw DecodingError.typeMismatch(JSONNull.self, DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Wrong type for JSONNull"))
}
}
public func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
try container.encodeNil()
}
}
这是我的 ObservableObject：
class UnsplashAPI: ObservableObject {
enum State {
case loading
case loaded(UnsplashData)
}
@Published var state = State.loading
let url = URL(string: "https://api.unsplash.com/")!
func request() {
guard var components = URLComponents(url: url.appendingPathComponent("photos/random"),
resolvingAgainstBaseURL: true)
else {
fatalError("Couldn't append path component")
}
components.queryItems = [
URLQueryItem(name: "client_id", value: "vMDQ3Vzix8FN6MJL5Qpl3y0F7GdQsTtOjBe_L-IG2ro")
]
let request = URLRequest(url: components.url!)
let urlSession = URLSession(configuration: URLSessionConfiguration.default)
urlSession.dataTask(with: request) { data, urlResponse, error in
if let data = data {
let decoder = JSONDecoder()
let dateFormatter = DateFormatter()
dateFormatter.locale = Locale(identifier: "en_US_POSIX")
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ssZ"
decoder.dateDecodingStrategy = .formatted(dateFormatter)
do {
let response = try decoder.decode(UnsplashData.self, from: data)
self.state = .loaded(response) //error here
} catch {
print(error)
fatalError("Couldn't decode")
}
} else if let error = error {
print(error.localizedDescription)
} else {
fatalError("Didn't receive data")
}
}.resume()
}
}
最后，这是我使用 Postman 请求的示例响应：
{
"id": "HWx5PYGudcI",
"created_at": "2020-12-08T22:11:11-05:00",
"updated_at": "2020-12-26T23:19:29-05:00",
"promoted_at": "2020-12-09T03:14:06-05:00",
"width": 4000,
"height": 6000,
"color": "#8ca6a6",
"blur_hash": "LAD,r_D*_M?^%ER4%$-oyYp0m+WE",
"description": null,
"alt_description": "boy in gray crew neck shirt",
"urls": {
"raw": "https://images.unsplash.com/photo-1607483421673-181fb79394b3?ixid=MXwxMTU5MTR8MHwxfHJhbmRvbXx8fHx8fHx8&ixlib=rb-1.2.1",
"full": "https://images.unsplash.com/photo-1607483421673-181fb79394b3?crop=entropy&cs=srgb&fm=jpg&ixid=MXwxMTU5MTR8MHwxfHJhbmRvbXx8fHx8fHx8&ixlib=rb-1.2.1&q=85",
"regular": "https://images.unsplash.com/photo-1607483421673-181fb79394b3?crop=entropy&cs=tinysrgb&fit=max&fm=jpg&ixid=MXwxMTU5MTR8MHwxfHJhbmRvbXx8fHx8fHx8&ixlib=rb-1.2.1&q=80&w=1080",
"small": "https://images.unsplash.com/photo-1607483421673-181fb79394b3?crop=entropy&cs=tinysrgb&fit=max&fm=jpg&ixid=MXwxMTU5MTR8MHwxfHJhbmRvbXx8fHx8fHx8&ixlib=rb-1.2.1&q=80&w=400",
"thumb": "https://images.unsplash.com/photo-1607483421673-181fb79394b3?crop=entropy&cs=tinysrgb&fit=max&fm=jpg&ixid=MXwxMTU5MTR8MHwxfHJhbmRvbXx8fHx8fHx8&ixlib=rb-1.2.1&q=80&w=200"
},
"links": {
"self": "https://api.unsplash.com/photos/HWx5PYGudcI",
"html": "https://unsplash.com/photos/HWx5PYGudcI",
"download": "https://unsplash.com/photos/HWx5PYGudcI/download",
"download_location": "https://api.unsplash.com/photos/HWx5PYGudcI/download"
},
"categories": [],
"likes": 51,
"liked_by_user": false,
"current_user_collections": [],
"sponsorship": null,
"user": {
"id": "3Bj-zCFL4-g",
"updated_at": "2020-12-26T14:58:36-05:00",
"username": "owensito",
"name": "Owen Vangioni",
"first_name": "Owen",
"last_name": "Vangioni",
"twitter_username": null,
"portfolio_url": null,
"bio": "Capturing magical moments...\nInstagram: @owensitens 18 years",
"location": "Argentina ",
"links": {
"self": "https://api.unsplash.com/users/owensito",
"html": "https://unsplash.com/@owensito",
"photos": "https://api.unsplash.com/users/owensito/photos",
"likes": "https://api.unsplash.com/users/owensito/likes",
"portfolio": "https://api.unsplash.com/users/owensito/portfolio",
"following": "https://api.unsplash.com/users/owensito/following",
"followers": "https://api.unsplash.com/users/owensito/followers"
},
"profile_image": {
"small": "https://images.unsplash.com/profile-1583211530737-0c1a46227535image?ixlib=rb-1.2.1&q=80&fm=jpg&crop=faces&cs=tinysrgb&fit=crop&h=32&w=32",
"medium": "https://images.unsplash.com/profile-1583211530737-0c1a46227535image?ixlib=rb-1.2.1&q=80&fm=jpg&crop=faces&cs=tinysrgb&fit=crop&h=64&w=64",
"large": "https://images.unsplash.com/profile-1583211530737-0c1a46227535image?ixlib=rb-1.2.1&q=80&fm=jpg&crop=faces&cs=tinysrgb&fit=crop&h=128&w=128"
},
"instagram_username": "owensitens",
"total_collections": 1,
"total_likes": 13,
"total_photos": 135,
"accepted_tos": true
},
"exif": {
"make": "NIKON CORPORATION",
"model": "NIKON D3300",
"exposure_time": "1/320",
"aperture": "5.3",
"focal_length": "45.0",
"iso": 200
},
"location": {
"title": null,
"name": null,
"city": null,
"country": null,
"position": {
"latitude": null,
"longitude": null
}
},
"views": 536045,
"downloads": 1267
}
您需要将线程切换到 main thread from which you are allowed (and only from it!) to make UI changes in iOS. To fix the error you will need to use GCD 并简单地将更改状态的行换行到 async 闭包块中。
DispatchQueue.main.async {
self.state = .loaded(response) // error should not be triggered anymore
}
在您的 class 定义之前添加 @MainActor。
我正在尝试从 Unsplash API 获取数据，但是我收到以下错误：“不允许从后台线程发布更改；确保从主线程发布值（通过像这样的运算符在模型更新时接收（on :)）。
这是模型结构：
// MARK: - UnsplashData
struct UnsplashData: Codable {
let id: String
let createdAt, updatedAt, promotedAt: Date
let width, height: Int
let color, blurHash: String
let unsplashDataDescription: String?
let altDescription: String
let urls: Urls
let links: UnsplashDataLinks
let categories: [String]
let likes: Int
let likedByUser: Bool
let currentUserCollections: [String]
let sponsorship: JSONNull?
let user: User
let exif: Exif
let location: Location
let views, downloads: Int
enum CodingKeys: String, CodingKey {
case id
case createdAt = "created_at"
case updatedAt = "updated_at"
case promotedAt = "promoted_at"
case width, height, color
case blurHash = "blur_hash"
case unsplashDataDescription = "description"
case altDescription = "alt_description"
case urls, links, categories, likes
case likedByUser = "liked_by_user"
case currentUserCollections = "current_user_collections"
case sponsorship, user, exif, location, views, downloads
}
}
// MARK: - Exif
struct Exif: Codable {
let make, model, exposureTime, aperture: String
let focalLength: String
let iso: Int
enum CodingKeys: String, CodingKey {
case make, model
case exposureTime = "exposure_time"
case aperture
case focalLength = "focal_length"
case iso
}
}
// MARK: - UnsplashDataLinks
struct UnsplashDataLinks: Codable {
let linksSelf, html, download, downloadLocation: String
enum CodingKeys: String, CodingKey {
case linksSelf = "self"
case html, download
case downloadLocation = "download_location"
}
}
// MARK: - Location
struct Location: Codable {
let title, name, city, country: String?
let position: Position
}
// MARK: - Position
struct Position: Codable {
let latitude, longitude: Double?
}
// MARK: - Urls
struct Urls: Codable {
let raw, full, regular, small: String
let thumb: String
}
// MARK: - User
struct User: Codable {
let id: String
let updatedAt: Date
let username, name, firstName, lastName: String
let twitterUsername: String?
let portfolioURL: String
let bio: String?
let location: String
let links: UserLinks
let profileImage: ProfileImage
let instagramUsername: String
let totalCollections, totalLikes, totalPhotos: Int
let acceptedTos: Bool
enum CodingKeys: String, CodingKey {
case id
case updatedAt = "updated_at"
case username, name
case firstName = "first_name"
case lastName = "last_name"
case twitterUsername = "twitter_username"
case portfolioURL = "portfolio_url"
case bio, location, links
case profileImage = "profile_image"
case instagramUsername = "instagram_username"
case totalCollections = "total_collections"
case totalLikes = "total_likes"
case totalPhotos = "total_photos"
case acceptedTos = "accepted_tos"
}
}
// MARK: - UserLinks
struct UserLinks: Codable {
let linksSelf, html, photos, likes: String
let portfolio, following, followers: String
enum CodingKeys: String, CodingKey {
case linksSelf = "self"
case html, photos, likes, portfolio, following, followers
}
}
// MARK: - ProfileImage
struct ProfileImage: Codable {
let small, medium, large: String
}
// MARK: - Encode/decode helpers
class JSONNull: Codable, Hashable {
public static func == (lhs: JSONNull, rhs: JSONNull) -> Bool {
return true
}
public var hashValue: Int {
return 0
}
public func hash(into hasher: inout Hasher) {
// No-op
}
public init() {}
public required init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
if !container.decodeNil() {
throw DecodingError.typeMismatch(JSONNull.self, DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Wrong type for JSONNull"))
}
}
public func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
try container.encodeNil()
}
}
这是我的 ObservableObject：
class UnsplashAPI: ObservableObject {
enum State {
case loading
case loaded(UnsplashData)
}
@Published var state = State.loading
let url = URL(string: "https://api.unsplash.com/")!
func request() {
guard var components = URLComponents(url: url.appendingPathComponent("photos/random"),
resolvingAgainstBaseURL: true)
else {
fatalError("Couldn't append path component")
}
components.queryItems = [
URLQueryItem(name: "client_id", value: "vMDQ3Vzix8FN6MJL5Qpl3y0F7GdQsTtOjBe_L-IG2ro")
]
let request = URLRequest(url: components.url!)
let urlSession = URLSession(configuration: URLSessionConfiguration.default)
urlSession.dataTask(with: request) { data, urlResponse, error in
if let data = data {
let decoder = JSONDecoder()
let dateFormatter = DateFormatter()
dateFormatter.locale = Locale(identifier: "en_US_POSIX")
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ssZ"
decoder.dateDecodingStrategy = .formatted(dateFormatter)
do {
let response = try decoder.decode(UnsplashData.self, from: data)
self.state = .loaded(response) //error here
} catch {
print(error)
fatalError("Couldn't decode")
}
} else if let error = error {
print(error.localizedDescription)
} else {
fatalError("Didn't receive data")
}
}.resume()
}
}
最后，这是我使用 Postman 请求的示例响应：
{
"id": "HWx5PYGudcI",
"created_at": "2020-12-08T22:11:11-05:00",
"updated_at": "2020-12-26T23:19:29-05:00",
"promoted_at": "2020-12-09T03:14:06-05:00",
"width": 4000,
"height": 6000,
"color": "#8ca6a6",
"blur_hash": "LAD,r_D*_M?^%ER4%$-oyYp0m+WE",
"description": null,
"alt_description": "boy in gray crew neck shirt",
"urls": {
"raw": "https://images.unsplash.com/photo-1607483421673-181fb79394b3?ixid=MXwxMTU5MTR8MHwxfHJhbmRvbXx8fHx8fHx8&ixlib=rb-1.2.1",
"full": "https://images.unsplash.com/photo-1607483421673-181fb79394b3?crop=entropy&cs=srgb&fm=jpg&ixid=MXwxMTU5MTR8MHwxfHJhbmRvbXx8fHx8fHx8&ixlib=rb-1.2.1&q=85",
"regular": "https://images.unsplash.com/photo-1607483421673-181fb79394b3?crop=entropy&cs=tinysrgb&fit=max&fm=jpg&ixid=MXwxMTU5MTR8MHwxfHJhbmRvbXx8fHx8fHx8&ixlib=rb-1.2.1&q=80&w=1080",
"small": "https://images.unsplash.com/photo-1607483421673-181fb79394b3?crop=entropy&cs=tinysrgb&fit=max&fm=jpg&ixid=MXwxMTU5MTR8MHwxfHJhbmRvbXx8fHx8fHx8&ixlib=rb-1.2.1&q=80&w=400",
"thumb": "https://images.unsplash.com/photo-1607483421673-181fb79394b3?crop=entropy&cs=tinysrgb&fit=max&fm=jpg&ixid=MXwxMTU5MTR8MHwxfHJhbmRvbXx8fHx8fHx8&ixlib=rb-1.2.1&q=80&w=200"
},
"links": {
"self": "https://api.unsplash.com/photos/HWx5PYGudcI",
"html": "https://unsplash.com/photos/HWx5PYGudcI",
"download": "https://unsplash.com/photos/HWx5PYGudcI/download",
"download_location": "https://api.unsplash.com/photos/HWx5PYGudcI/download"
},
"categories": [],
"likes": 51,
"liked_by_user": false,
"current_user_collections": [],
"sponsorship": null,
"user": {
"id": "3Bj-zCFL4-g",
"updated_at": "2020-12-26T14:58:36-05:00",
"username": "owensito",
"name": "Owen Vangioni",
"first_name": "Owen",
"last_name": "Vangioni",
"twitter_username": null,
"portfolio_url": null,
"bio": "Capturing magical moments...\nInstagram: @owensitens 18 years",
"location": "Argentina ",
"links": {
"self": "https://api.unsplash.com/users/owensito",
"html": "https://unsplash.com/@owensito",
"photos": "https://api.unsplash.com/users/owensito/photos",
"likes": "https://api.unsplash.com/users/owensito/likes",
"portfolio": "https://api.unsplash.com/users/owensito/portfolio",
"following": "https://api.unsplash.com/users/owensito/following",
"followers": "https://api.unsplash.com/users/owensito/followers"
},
"profile_image": {
"small": "https://images.unsplash.com/profile-1583211530737-0c1a46227535image?ixlib=rb-1.2.1&q=80&fm=jpg&crop=faces&cs=tinysrgb&fit=crop&h=32&w=32",
"medium": "https://images.unsplash.com/profile-1583211530737-0c1a46227535image?ixlib=rb-1.2.1&q=80&fm=jpg&crop=faces&cs=tinysrgb&fit=crop&h=64&w=64",
"large": "https://images.unsplash.com/profile-1583211530737-0c1a46227535image?ixlib=rb-1.2.1&q=80&fm=jpg&crop=faces&cs=tinysrgb&fit=crop&h=128&w=128"
},
"instagram_username": "owensitens",
"total_collections": 1,
"total_likes": 13,
"total_photos": 135,
"accepted_tos": true
},
"exif": {
"make": "NIKON CORPORATION",
"model": "NIKON D3300",
"exposure_time": "1/320",
"aperture": "5.3",
"focal_length": "45.0",
"iso": 200
},
"location": {
"title": null,
"name": null,
"city": null,
"country": null,
"position": {
"latitude": null,
"longitude": null
}
},
"views": 536045,
"downloads": 1267
}
您需要将线程切换到 main thread from which you are allowed (and only from it!) to make UI changes in iOS. To fix the error you will need to use GCD 并简单地将更改状态的行换行到 async 闭包块中。
DispatchQueue.main.async {
self.state = .loaded(response) // error should not be triggered anymore
}
在您的 class 定义之前添加 @MainActor。