我正在尝试添加一个throws使用完成处理程序添加到我现有的函数，但我不断收到警告说no calls throwing functions occur within try expression。在我抛出错误的部分中，我收到一条错误消息
从“() throwing -> Void”类型的抛出函数到非抛出函数类型的转换无效。
enum LoginError: ErrorType {
case Invalid_Credentials
case Unable_To_Access_Login
case User_Not_Found
}
@IBAction func loginPressed(sender: AnyObject) {
do{
try self.login3(dict, completion: { (result) -> Void in
if (result == true)
{
self.performSegueWithIdentifier("loginSegue", sender: nil)
}
})
}
catch LoginError.User_Not_Found
{
//deal with it
}
catch LoginError.Unable_To_Access_Login
{
//deal with it
}
catch LoginError.Invalid_Credentials
{
//deal with it
}
catch
{
print("i dunno")
}
}
func login3(params:[String: String], completion: (result:Bool) throws -> Void)
{
//Request set up
let task = session.dataTaskWithRequest(request, completionHandler: {data, response, error -> Void in
do {
let json = try NSJSONSerialization.JSONObjectWithData(data, options: .MutableLeaves) as? NSDictionary
if let parseJSON = json
{
let userID = parseJSON["user_id"] as? Int
let loginError = parseJSON["user_not_found"] as? String
let validationError = parseJSON["invalid_credentials"] as? String
let exception = parseJSON["unable_to_access_login"] as? String
var responseArray = [(parseJSON["user_id"] as? Int)]
if userID != nil
{
dispatch_async(dispatch_get_main_queue()) {
completion(result:true)
}
}
else if loginError != ""
{
dispatch_async(dispatch_get_main_queue()){
completion(result: false)
self.loginErrorLabel.text = loginError
throw LoginError.User_Not_Found
}
}
else if validationError != ""
{
dispatch_async(dispatch_get_main_queue()){
completion(result:false)
self.validationErrorLabel.text = validationError
throw LoginError.Invalid_Credentials
}
}
else if exception != nil
{
dispatch_async(dispatch_get_main_queue()){
completion(result:false)
self.exceptionErrorLabel.text = "Unable to login"
throw LoginError.Unable_To_Access_Login
}
}
}
else
{
}
}
catch let parseError {
// Log the error thrown by `JSONObjectWithData`
})
task.resume()
}
您可以做的是将错误封装到可抛出的闭包中，如下面的代码所示，以实现您想要的：
func login3(params:[String: String], completion: (inner: () throws -> Bool) -> ()) {
let task = session.dataTaskWithRequest(request, completionHandler: { data, response, error -> Void in
let json = try NSJSONSerialization.JSONObjectWithData(data, options: .MutableLeaves) as? NSDictionary
if let parseJSON = json {
let userID = parseJSON["user_id"] as? Int
let loginError = parseJSON["user_not_found"] as? String
let validationError = parseJSON["invalid_credentials"] as? String
let exception = parseJSON["unable_to_access_login"] as? String
var responseArray = [(parseJSON["user_id"] as? Int)]
if userID != nil {
dispatch_async(dispatch_get_main_queue()) {
completion(inner: { return true })
}
}
else if loginError != ""
{
dispatch_async(dispatch_get_main_queue()) {
self.loginErrorLabel.text = loginError
completion(inner: { throw LoginError.User_Not_Found })
}
}
else if validationError != ""
{
dispatch_async(dispatch_get_main_queue()) {
self.validationErrorLabel.text = validationError
completion(inner: {throw LoginError.Invalid_Credentials})
}
}
else if exception != nil
{
dispatch_async(dispatch_get_main_queue()){
self.exceptionErrorLabel.text = "Unable to login"
completion(inner: {throw LoginError.Unable_To_Access_Login})
}
}
}
else
{
}
}
task.resume()
}
您可以通过以下方式调用它：
self.login3(dict) { (inner: () throws -> Bool) -> Void in
do {
let result = try inner()
self.performSegueWithIdentifier("loginSegue", sender: nil)
} catch let error {
print(error)
}
}
诀窍是login3函数需要一个额外的闭包，称为'inner'类型的() throws -> Bool。这个闭包要么提供计算结果，要么抛出异常。闭包本身是在计算过程中通过以下两种方式之一构建的：
- 如果出现错误：
inner: {throw error}
- 如果成功：
inner: {return result}
我强烈推荐您一篇关于使用的优秀文章try/catch在异步调用中在 Swift 中使用 try / catch 和异步闭包 http://appventure.me/2015/06/19/swift-try-catch-asynchronous-closures/
我希望这对你有帮助。
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