iTunes API 抓取（JSON）

iTunes Search API 的文件

以 iTunes 搜尋 swift 當例子

API 的網址為:

https://itunes.apple.com/search?term=swift&media=music&country=tw

可以用 JSON Editor online 看一下內容。

解析時要一層一層的解

先用playground測試

這是第一層：

解析：

struct SearchResponse: Codable {
       let resultCount: Int
       let results: []
   }

results :[] 因為還不知道 array 成員的型別，所以先寫 [ ]。

這是第二層：

定義型別： StoreItem

解析：

 struct StoreItem: Codable {
    let trackId: Int
    let artistName: String
    let trackName: String
    let collectionName: String?
    let previewUrl: URL
    let artworkUrl100: URL
    let trackPrice: Double?
    let isStreamable: Bool?
}

然後 results :[] 改成 results: [StoreItem]

程式碼：

struct SearchResponse: Codable {
       let resultCount: Int
       let results: [StoreItem]
   }

struct StoreItem: Codable {
    let trackId: Int
    let artistName: String
    let trackName: String
    let collectionName: String?
    let previewUrl: URL
    let artworkUrl100: URL
    let trackPrice: Double?
    let isStreamable: Bool?
}

第二種寫法

SearchResponse 包住 StoreItem

struct SearchResponse: Codable {
       let resultCount: Int
       let results: [StoreItem]
    struct StoreItem: Codable {
        let trackId: Int
        let artistName: String
        let trackName: String
        let collectionName: String?
        let previewUrl: URL
        let artworkUrl100: URL
        let trackPrice: Double?
        let isStreamable: Bool?
    }
   }

注意

有些 property 被宣告為 optional
因為 JSON 裡有些 key 不會每一筆資料都有
比方不是每首歌都可以買，所以不一定有 trackPrice
不一定會有的 collectionName，trackPrice & isStreamable 設為 optional
如果沒有設為 optional，到時候一旦發現沒有這些欄位，將造成轉換失敗。

測試 JSON 解碼是否成功

方法 1: 使用 async & await

let urlString = "https://itunes.apple.com/search?term=swift&media=music&country=tw"
if let url = URL(string: urlString) {
    Task {
        do {
            let (data, _) = try await URLSession.shared.data(from: url)
            let decoder = JSONDecoder()
            let searchResponse = try decoder.decode(SearchResponse.self, from: data)
            print(searchResponse.results)
        } catch {
            print(error)
        }
    }
}

方法 2: 使用 completion handler

let urlString = "https://itunes.apple.com/search?term=swift&media=music&country=tw"

if let url = URL(string: urlString) {
    URLSession.shared.dataTask(with: url){
        data, response, error
        in
        if let data {
            let decoder = JSONDecoder()
            do {
                let searchResponse = try decoder.decode(SearchResponse.self, from: data)
            } catch  {
                print(error)
            }
        } 
    }.resume()
}

中文搜尋會不一樣

需要加上一段程式碼：

.addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed),

完整程式碼：

if let urlString = "https://itunes.apple.com/search?term=伍佰&media=music&country=tw".addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed),
   let url = URL(string: urlString){
    URLSession.shared.dataTask(with: url){
        data, response, error
        in
        if let data {
            let decoder = JSONDecoder()
            do {
                let searchResponse = try decoder.decode(SearchResponse.self, from: data)
                let itme = searchResponse.results[1]
                print(itme.trackName, itme.previewUrl)
            } catch  {
                print(error)
            }
        }
    }.resume()
}

練習檔案
0927jsonDemoiTunesPG.zip