Implement Delegate with Closure in Swift?
You can't define an anonymous class, but you can define a local class that works very similarly. I've actually migrated away from the inline class approach as the REPL seems to have problems with it even though it seems to be fine with the compiler. The approach I'm now using is to define a glue class which forwards methods to closures defined in the init, so it all feels very natural.
The URLConnectionDataDelegate is defined as:
class GreenUrlConnectionDataDelegate: NSObject, NSURLConnectionDataDelegate {
var didFinishLoading:()->()
var didReceiveResponse:((NSURLResponse!)->())?
var didReceiveData:((NSData!)->())?
var didFailWithError:((NSError!)->())?
func connectionDidFinishLoading(conn:NSURLConnection!) {
didFinishLoading()
}
func connection(conn:NSURLConnection!, didReceiveResponse response:NSURLResponse!) {
didReceiveResponse?(response)
}
func connection(conn:NSURLConnection!, didReceiveData data:NSData!) {
didReceiveData?(data)
}
func connection(conn:NSURLConnection!, didFailWithError error:NSError!) {
didFailWithError?(error)
}
init(
didFinishLoading:@escaping ()->(),
didReceiveResponse:@escaping ((NSURLResponse!)->())? = nil,
didReceiveData:@escaping ((NSData!)->())? = nil,
didFailWithError:@escaping ((NSError!)->())? = nil
) {
self.didFinishLoading = didFinishLoading
self.didReceiveResponse = didReceiveResponse
self.didReceiveData = didReceiveData
self.didFailWithError = didFailWithError
}
}
Which allows me to define a function with an inline delegate:
func downloadUrl(string:String, completion:(data:NSData?, error:NSError?) -> ()) {
let url = NSURL(string:string)
let request = NSURLRequest(URL: url)
var received:NSMutableData! = nil
let conn = NSURLConnection(request: request, delegate: GreenUrlConnectionDataDelegate(
didFinishLoading:{
completion(data:received, error:nil)
},
didReceiveResponse:{response in
if let capacity = response?.expectedContentLength {
if capacity > 0 {
received = NSMutableData(capacity: Int(capacity))
}
else {
received = NSMutableData()
}
}
},
didReceiveData:{data in
if data != nil {
received.appendData(data)
}
},
didFailWithError:{error in
completion(data:nil, error:error)
}
)
)
}
And the code to test it out in a playground:
downloadUrl("http://www.google.com") {
(data:NSData?, error:NSError?) -> () in
println("completion")
println("data.size: \(data?.length)")
println("error: \(error?.localizedDescription)")
}
XCPSetExecutionShouldContinueIndefinitely()
You could conceivably even embed the glue class into an extension to the class requiring the delegate, although I haven't tried that out yet.