Xcode 15.3 iOS Playground中Async/Await执行异常原因及修复

错误原因 #

Xcode Playground的默认执行逻辑会在主线程任务结束后终止运行，但你的代码使用了异步await调用。尽管异步任务已完成并输出结果，但Playground未检测到明确的持续运行标记，误以为执行意外中断，因此抛出该错误。本质是Playground对异步代码的执行生命周期处理逻辑和常规iOS项目不同。

修复方法 #

只需在代码开头添加一行标记，告知Playground保持运行状态直到手动结束，修改后的代码如下：

import Foundation
import PlaygroundSupport

// 让Playground持续运行，直到主动结束
PlaygroundPage.current.needsIndefiniteExecution = true

func fetchWeatherHistory() async -> [Double] {
    (1...100).map { _ in Double.random(in: -10...30) }
}

func calculateAverageTemperature(for records: [Double]) async -> Double {
    let total = records.reduce(0, +)
    let average = total / Double(records.count)
    return average
}

func upload(result: Double) async -> String {
    "OKet"
}

func processWeather() async throws {
    let records = await fetchWeatherHistory()
    let average = await calculateAverageTemperature(for: records)
    let response = await upload(result: average)
    print("Server response: \(response)")
    // 异步任务完成后主动终止Playground
    PlaygroundPage.current.finishExecution()
}

do {
    try await processWeather()
} catch let error {
    print(error.localizedDescription)
    PlaygroundPage.current.finishExecution()
}

注：代码中把无需重新赋值的var改为let是规范优化操作，并非修复错误的必要步骤。

内容的提问来源于stack exchange，提问作者The Outstanding Question Asker