I'm new to Swift code formatting and I'm trying to figure out how to use the UIAccessibilityRequestGuidedAccess function. Here's how the function is declared in Swift:
func UIAccessibilityRequestGuidedAccessSession(_ enable: Bool,
_ completionHandler: ((Bool) -> Void)!)
In Objective-C I would have used it as follows:
UIAccessibilityRequestGuidedAccessSession(YES, ^(BOOL didSucceed) {
if (didSucceed ) {
...
} else {
...
}
Any help with the syntax is appreciated.
You do it like this:
UIAccessibilityRequestGuidedAccessSession(true){
success in
println("Request guided access success \(success)")
}
YES is not valid in swift (use true/false), and if the last parameter of a function is a closure, you can use trailing closure syntax as shown above. success is the argument passed into the completion block.
Related
func startUpdates(from start: Date,
withHandler handler: #escaping CMPedometerHandler)
typealias CMPedometerHandler = (CMPedometerData?, Error?) -> Void
The above function retrieves the pedometer data from your iOS device. When I called the function the only argument I need passed to is the parameter from start.
Who actually initialized the parameter list of the completion handler closure? The startUpdates function I've called?
When I called the function the only argument I need to passed to is the parameter from start
That's not true.
You have to pass also the closure as second parameter. The closure itself is called by the startUpdates function after doing its work and passes two parameters back, an optional Data and an optional Error instance.
The functional programming is a very convenient way to be able to run arbitrary code (in the closure).
You can declare the closure separately
let result : CMPedometerHandler = { data, error in
if let error = error { print(error); return }
// do something with the data
}
startUpdates(from: Date(), withHandler: result)
or inline
startUpdates(from: Date(), withHandler: { data, error in
if let error = error { print(error); return }
// do something with the data
})
or with trailing closure syntax
startUpdates(from: Date()) { data, error in
if let error = error { print(error); return }
// do something with the data
}
I have the following code snippet.
camera.onDeviceChange = { [weak self] (camera: LLSimpleCamera!, device: AVCaptureDevice!) -> Void in
print("Device changed.")
}
This used to work fine in Swift 2, but now I am getting the following error message:
Cannot assign value of type '(LLSimpleCamera!, AVCaptureDevice!) -> Void' to type '((LLSimpleCamera?, AVCaptureDevice?) -> Void)!'
Not really sure how to change this, I tried matching the type by changing the ! to optionals and then adding ! after the void, however this didn't work.
Your error suggest type mismatch that means LLSimpleCamera! != LLSimpleCamera? .. there is no need to define type. .. you can use it something like
camera.onDeviceChange = { [weak self] (camera, device) -> Void in
print("Device changed.")
}
I have working project in Xcode 7.3 with swift 2.2 version. Now I have updated Xcode 8 and migrated to swift 3. Now my project contains errors specially for blocks like success block of afnetworking.
Which gives error as
Cannot convert value of type '() -> ()' to expected argument type '((URLSessionDataTask, Any?) -> Void)?'
I don't understand how to solve this to work as per swift 3.
And there is also same like error in Facebook login.
Which gives error as
Cannot convert value of type '(FBSDKLoginManagerLoginResult!, NSError!) -> Void' to expected argument type 'FBSDKLoginManagerRequestTokenHandler!'
and
Cannot convert value of type '(_, _, NSError!) -> Void' to expected argument type 'FBSDKGraphRequestHandler!'
This all errors are related to handler blocks in swift 3. I don't understand the errors and so that can't able to solve. Any help will be appreciated. Thanks in advance.
For facebook - the problem is in new Swift rules about converting objective-c function parameters into Swift.
Previously, if parameters in objective-c code did not have nullability attributes(like nonnull or nullable), Swift converts it with ! making them non optional(forced unwrapping). Now it convert it with ? making them optional. That why you are getting an error. Before you were putting as a callback for login:
(FBSDKLoginManagerLoginResult!, NSError!) -> Void
Now you need to put:
(FBSDKLoginManagerLoginResult?, Error?) -> Void
Also, as you see, now you will not see NSError class. Instead of that Swift will put Error.This is also new rule. Now all "NS" prefixed in class names is removed in Swift(NSObject -> Object; NSError -> Error).
Example of working code for facebook login in Swift 3.0:
let manager = FBSDKLoginManager()
manager.logIn(withReadPermissions: ["public_profile"], from: self.controller) {
(loginResult: FBSDKLoginManagerLoginResult?, error: Error?) in
}
Example of working code for facebook request in Swift 3.0:
let request = FBSDKGraphRequest()
request.start {
(connection: FBSDKGraphRequestConnection?, result: Any?, error: Error?) in
}
As you see, now it is using Any type instead of objective-c id. In Swift 2.2 it was using AnyObject. It is also new Swift converting rule.
You do not need to specify callback parameters type. I did that in code for highlighting their real types. So you can just write code without them:
let manager = FBSDKLoginManager()
manager.logIn(withReadPermissions: ["public_profile"], from: self.controller) { (loginResult, error) in }
let request = FBSDKGraphRequest()
request.start { (connection, result, error) in }
But you need to remember that they are optional now.
In conclusion some converting rules that may affect you callback code:
Closure parameters are optional if in objective-c are not specified nullability attributes
All "NS" prefixes is removed for objective-c classes in Swift
If objective-c function had id parameter, in Swift 3.0 it will have type Any instead of AnyObject
Though I didn't know the error before that what Xcode want to inform me about the error, but I have removed type specification with object and it worked.
As
manager.post(methodname, parameters: param, progress: nil, success:{ (dataTask, responseObj) in
if let dict : NSDictionary = responseObj as? NSDictionary {
print("Response of \(methodname) : \(dict)")
if dict.object(forKey: "response") as? String == "success" {
CompletionHandler(true, dict)
} else {
CompletionHandler(false, dict)
}
}
})
Here with respect to question error is given at dataTask and responseObj which are with type specified. After removing type it worked fine.
Same as with facebook login
#IBAction func fbLoginClicked(_ sender: AnyObject) {
let app = UIApplication.shared.delegate as! AppDelegate
app.fbLoginManager = FBSDKLoginManager()
app.fbLoginManager.logOut()
app.fbLoginManager.loginBehavior = FBSDKLoginBehavior.native
app.fbLoginManager.logIn(withReadPermissions: ["email"], from: self, handler: { (result, error) -> Void in
if error != nil {
print(error?.localizedDescription)
} else {
if (result! as FBSDKLoginManagerLoginResult).isCancelled == true {
} else {
self.fetchFacebookUserDetail()
}
}
})
}
Here also I have removed type specification of result and error and problem solved. And followed this in whole app and it worked. I can run the project without error and also it is working. Thanks.
I am trying to call a swift method, which is implemented like this:-
#objc class DataAPI: NSObject {
func makeGet(place:NSString , completionHandler: (String! , Bool!) -> Void)
{
var str:String = ""
let manager = AFHTTPSessionManager()
manager.GET("https://api.com", parameters: nil, success:
{ (operation, responseObject) -> Void in
str = "JSON: \(responseObject!.description)"
print(str)
completionHandler(str,false) //str as response json, false as error value
},
failure: { (operation,error: NSError!) in
str = "Error: \(error.localizedDescription)"
completionHandler("Error",true)
})
}}
Now when I am trying to call it in my Objective C class, it is throwing an error "No Visible interface for DataAPI declares selector makeGet:completionHandler"
This is how I am calling the method in my Objective C class:-
[[DataAPI new] makeGet:#"" completionHandler:^{
}];
Try to clean and Rebuild to generate the "YourModule-Swift.h" again with all your changes.
Then it should be something like this:
[[DataAPI new] makeGet:#"" withCompletionHandler:^(NSString* string, BOOl b){
// your code here
}];
If you still getting that error, your "YourModule-Swift.h" file hasn't been generated correctly. Check it!
I see that in Swift the completion handler has two arguments: String and Bool whereas in your Objective-C call you pass a block without any arguments. I think it may be the cause of the error.
Try:
[[DataAPI new] makeGet:#"" completionHandler:^(NSString* string, BOOl b){
}];
You shouldn't use !(ImplicitUnwrappedOptional) keyword in closure. That is not allow bridging to ObjC code. just remove ! from closure.
func makeGet(place:NSString , completionHandler: (String! , Bool!) -> Void)
to
func makeGet(place:NSString , completionHandler: (String , Bool) -> Void)
I would like to call a completion block in Swift as I have always done in Objective-C. I took a look at closures, but for some reason, I cannot get it to work...
Obj-C:
- (void)someMethodWithParam1:(NSString *)param completion:(void(^)(NSArray* arr, NSURLResponse *resp))callback
{
callback(arr, resp);
}
Swift:
func someMethodWithParam1(param: NSString, completion:((NSArray?, NSURLResponse?)->())) ->(){
^
|
/* Error: Insert ',' here */
completion(arr, resp)
}
EDIT
Okay, it was not a syntactical error, but an error from my side. The method header I used here is different from the one in my code. So this code that I originally posted should work fine.
Typealias's are your friend here, just to make the code more readable
typealias onComplete = (NSArray?, NSURLResponse?) -> ()
func someMethodWithParam1(param: NSString, completion:onComplete) -> ()
{
completion(arr, resp)
}