无法用类型为'（_）'的参数列表调用'perform'

Question

为什么这个Square示例直接针对他们的README不起作用？

let callbackURL = URL(string: "OdinMobile://")! 
    do { 
     let amount = try SCCMoney(amountCents: money, currencyCode: "USD") 

     let request : SCCAPIRequest = 
      try SCCAPIRequest(
       callbackURL: callbackURL, 
       amount: amount, 
       userInfoString: userInfoString, 
       merchantID: nil, 
       notes: notes, 
       customerID: nil, 
       supportedTenderTypes: supportedTenderTypes, 
       clearsDefaultFees: clearsDefaultFees, 
       returnAutomaticallyAfterPayment: true 
      ) 

    } catch let error as NSError { 
     print(error.localizedDescription) 
    } 

    do { 
     try SCCAPIConnection.perform(request) 
    } catch let error as NSError { 
     print(error.localizedDescription) 
    } 

我得到一个Cannot invoke 'perform' with an argument list of type '(_)'与Overloads for 'perform' exist with these partially matching parameter lists: (SCCAPIRequest), (Selector!)的附加消息。我想让request成为SCCAPIRequest，为什么它不能作为一个阅读？是因为它在do区块吗？

Answer 1

的do关键字创建其大括号内部的范围，像一个if或for循环，这意味着在创建请求是第一范围内以及在所述第二不可​​用。由于在这两种情况下，您都会在相同的情况下执行相同的操作，因此您可以在同一范围内调用perform调用。

let callbackURL = URL(string: "OdinMobile://")! 
do { 
    let amount = try SCCMoney(amountCents: money, currencyCode: "USD") 

    let request : SCCAPIRequest = 
     try SCCAPIRequest(
      callbackURL: callbackURL, 
      amount: amount, 
      userInfoString: userInfoString, 
      merchantID: nil, 
      notes: notes, 
      customerID: nil, 
      supportedTenderTypes: supportedTenderTypes, 
      clearsDefaultFees: clearsDefaultFees, 
      returnAutomaticallyAfterPayment: true 
     ) 
    try SCCAPIConnection.perform(request) 
} catch let error as NSError { 
    print(error.localizedDescription) 
}