将完成块从swift传递回目标

// 定义一个异步函数，接受一个完成块作为参数
func fetchData(completion: @escaping (Result<String, Error>) -> Void) {
    // 模拟异步操作
    DispatchQueue.global().async {
        // 模拟成功和失败的情况
        let success = Bool.random()
        if success {
            completion(.success("Data fetched successfully"))
        } else {
            completion(.failure(NSError(domain: "", code: -1, userInfo: [NSLocalizedDescriptionKey: "Failed to fetch data"])))
        }
    }
}

// 调用异步函数并传递完成块
fetchData { result in
    switch result {
    case .success(let data):
        print(data)
    case .failure(let error):
        print("Error: \(error.localizedDescription)")
    }
}

func fetchData(completion: @escaping (Result<String, Error>) -> Void) {
    DispatchQueue.global().async {
        // 模拟异步操作
        let success = Bool.random()
        if success {
            completion(.success("Data fetched successfully"))
        } else {
            completion(.failure(NSError(domain: "", code: -1, userInfo: [NSLocalizedDescriptionKey: "Failed to fetch data"])))
        }
    }
}

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        fetchData { [weak self] result in
            // 处理结果
        }
    }
}

fetchData { result in
    DispatchQueue.main.async {
        switch result {
        case .success(let data):
            // 更新UI
            print(data)
        case .failure(let error):
            // 更新UI
            print("Error: \(error.localizedDescription)")
        }
    }
}