iOS集成PayPal-Braintree支付时BTAPIClient可选类型解包报错如何解决

问题根因 #

你遇到的报错本质是Swift可选类型的类型匹配问题：
你定义的braintreeClient是可选类型BTAPIClient?，而BTPayPalDriver初始化要求传入非可选的BTAPIClient实例，直接传可选值就会触发该报错。另外你当前的代码还有两个隐藏问题会导致后续报错：

1. 初始化BTAPIClient的授权字符串末尾多了一个空格，会直接导致初始化失败，braintreeClient变成nil
2. 你实现的BTViewControllerPresentingDelegate代理方法是空的，就算解包成功也无法弹出支付页面

修正方案 #

你可以用guard let安全解包可选值，同时补全代理逻辑、修正授权字符串即可，核心代码修改如下：

import UIKit
import Braintree

class MyViewController: UIViewController {
    // 可以保持可选类型
    var braintreeClient: BTAPIClient?

    override func viewDidLoad() {
        super.viewDidLoad()
        // 去掉授权字符串末尾的多余空格
        braintreeClient = BTAPIClient(authorization: "sandbox_bnkgmk59_5dxr37xvb54mg8sp")
    }

    @IBAction func clickedBtnPay(_ sender: Any) {
        // 安全解包braintreeClient，解包失败直接终止支付流程
        guard let client = braintreeClient else {
            print("BTAPIClient初始化失败，请检查授权字符串是否正确")
            return
        }
        // 用解包后的非可选值初始化
        let payPalDriver = BTPayPalDriver(apiClient: client)
        payPalDriver.viewControllerPresentingDelegate = self
        payPalDriver.appSwitchDelegate = self
        
        let request = BTPayPalRequest(amount: "2.32")
        request.currencyCode = "USD"

        payPalDriver.requestOneTimePayment(request) { (tokenizedPayPalAccount, error) in
            if let tokenizedPayPalAccount = tokenizedPayPalAccount {
                print("Got a nonce: \(tokenizedPayPalAccount.nonce)")
                // 后续处理拿到的nonce传给自己的服务端校验
            } else if let error = error {
                print("支付出错：\(error.localizedDescription)")
            } else {
                print("用户取消支付")
            }
        }
    }
}

extension MyViewController: BTViewControllerPresentingDelegate {
    func paymentDriver(_ driver: Any, requestsPresentationOf viewController: UIViewController) {
        // 实现弹出支付页面的逻辑
        present(viewController, animated: true)
    }
  
    func paymentDriver(_ driver: Any, requestsDismissalOf viewController: UIViewController) {
        // 实现关闭支付页面的逻辑
        dismiss(animated: true)
    }
}

extension MyViewController: BTAppSwitchDelegate {
    func appSwitcherWillPerformAppSwitch(_ appSwitcher: Any) {}
    func appSwitcher(_ appSwitcher: Any, didPerformSwitchTo target: BTAppSwitchTarget) {}
    func appSwitcherWillProcessPaymentInfo(_ appSwitcher: Any) {}
}

注意事项 #

• 不要用!强制解包可选值，一旦授权字符串错误、环境不匹配导致初始化失败，强制解包会直接触发App崩溃
• 如果你需要切换到生产环境，记得把授权字符串替换为生产环境的client token或tokenization key
• 拿到支付nonce之后需要传递到你的后端服务，调用Braintree的接口完成实际的交易校验和扣款

内容的提问来源于stack exchange，提问作者askit