Promise + progress + pause + cancel + retry for Swift.
See ReactKit Wiki page.
// define task
let task = Task<Float, String, NSError> { progress, fulfill, reject, configure in
player.doSomethingWithProgress({ (progressValue: Float) in
progress(progressValue) // optional
}, completion: { (value: NSData?, error: NSError?) in
if error == nil {
fulfill("OK")
}
else {
reject(error)
}
})
// pause/resume/cancel configuration (optional)
configure.pause = { [weak player] in
player?.pause()
}
configure.resume = { [weak player] in
player?.resume()
}
configure.cancel = { [weak player] in
player?.cancel()
}
}
// set success & failure
task.success { (value: String) -> Void in
// do something with fulfilled value
}.failure { (error: NSError?, isCancelled: Bool) -> Void in
// do something with rejected error
}
// you can call configured operations outside of Task-definition
task.pause()
task.resume()
task.cancel()Notice that player has following methods, which will work nicely with SwiftTask:
doSomethingWithProgress(_:completion:)(progress callback as optional)pause()(optional)resume()(optional)cancel()(optional)
One of the best example would be Alamofire (networking library) as seen below.
Using Alamofire
typealias Progress = (bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64)
typealias AlamoFireTask = Task<Progress, String, NSError>
// define task
let task = AlamoFireTask { progress, fulfill, reject, configure in
Alamofire.download(.GET, "http://httpbin.org/stream/100", destination: somewhere)
.progress { bytesWritten, totalBytesWritten, totalBytesExpectedToWrite in
progress((bytesWritten, totalBytesWritten, totalBytesExpectedToWrite) as Progress)
}.response { request, response, data, error in
if let error = error {
reject(error)
return
}
fulfill("OK")
}
return
}
// set progress & then
task.progress { (oldProgress: Progress?, newProgress: Progress) in
println("\(newProgress.bytesWritten)")
println("\(newProgress.totalBytesWritten)")
println("\(newProgress.totalBytesExpectedToWrite)")
}.then { (value: String?, errorInfo: AlamoFireTask.ErrorInfo?) -> Void in
// do something with fulfilled value or rejected errorInfo
}Task can retry for multiple times by using retry() method.
For example, task.retry(n) will retry at most n times (total tries = n+1) if task keeps rejected, and task.retry(0) is obviously same as task itself having no retries.
This feature is extremely useful for unstable tasks e.g. network connection.
By implementing retryable from SwiftTask's side, similar code is no longer needed for player (inner logic) class.
task.retry(2).progress { ... }.success { ...
// this closure will be called even when task is rejected for 1st & 2nd try
// but finally fulfilled in 3rd try.
}For more examples, please see XCTest cases.
Define your task inside initClosure.
let task = Task<Float, NSString?, NSError> { progress, fulfill, reject, configure in
player.doSomethingWithCompletion { (value: NSString?, error: NSError?) in
if error == nil {
fulfill(value)
}
else {
reject(error)
}
}
}In order to pipeline future task.value or task.errorInfo (tuple of (error: Error?, isCancelled: Bool)) via then()/success()/failure(), you have to call fulfill(value) and/or reject(error) inside initClosure.
Optionally, you can call progress(progressValue) multiple times before calling fulfill/reject to transfer progressValue outside of the initClosure, notifying it to task itself.
To add pause/resume/cancel functionality to your task, use configure to wrap up the original one.
// NOTE: use weak to let task NOT CAPTURE player via configure
configure.pause = { [weak player] in
player?.pause()
}
configure.resume = { [weak player] in
player?.resume()
}
configure.cancel = { [weak player] in
player?.cancel()
}task.progress { (oldProgress: Progress?, newProgress: Progress) in
println(newProgress)
return
}.success { ... }task.progress(progressClosure) will add progressClosure to observe old/new progressValue which is notified from inside previous initClosure. This method will return same task, so it is useful to chain with forthcoming then/success/failure.
task.then(thenClosure) will return a new task where thenClosure will be invoked when task is either fulfilled or rejected.
This case is similar to JavaScript's promise.then(onFulfilled, onRejected).
thenClosure can be two types of closure form:
thenClosure: (Value?, ErrorInfo?) -> Value2(flow: task => newTask)
// let task will be fulfilled with value "Hello"
task.then { (value: String?, errorInfo: ErrorInfo?) -> String in
// nil-check to find out whether task is fulfilled or rejected
if errorInfo == nil {
return "\(value!) World"
}
else {
return "\(value!) Error"
}
}.success { (value: String) -> Void in
println("\(value)") // Hello World
return"
}
thenClosure: (Value?, ErrorInfo?) -> Task(flow: task => task2 => newTask)
// let task will be fulfilled with value "Hello"
task.then { (value: String?, errorInfo: ErrorInfo?) -> Task<Float, String, NSError> in
if errorInfo == nil {
// let task2 will be fulfilled with value "\(value!) Swift"
let task2 = ...
return task2
}
else {
return someOtherTask
}
}.success { (value: String) -> Void in
println("\(value)") // Hello Swift
return"
}
Similar to then() method, task.success(successClosure) will return a new task, but this time, successClosure will be invoked when task is only fulfilled.
This case is similar to JavaScript's promise.then(onFulfilled).
// let task will be fulfilled with value "Hello"
task.success { (value: String) -> String in
return "\(value) World"
}.success { (value: String) -> Void in
println("\(value)") // Hello World
return"
}
Just the opposite of success(), task.failure(failureClosure) will return a new task where failureClosure will be invoked when task is only rejected/cancelled.
This case is similar to JavaScript's promise.then(undefined, onRejected) or promise.catch(onRejected).
// let task will be rejected with error "Oh My God"
task.success { (value: String) -> Void in
println("\(value)") // never reaches here
return
}.failure { (error: NSError?, isCancelled: Bool) -> Void in
println("\(error!)") // Oh My God
return
}See Retry-able section.
Task.all(tasks) is a new task that performs all tasks simultaneously and will be:
- fulfilled when all tasks are fulfilled
- rejected when any of the task is rejected
Task.any(tasks) is an opposite of Task.all(tasks) which will be:
- fulfilled when any of the task is fulfilled
- rejected when all tasks are rejected
Task.some(tasks) is a new task that performs all tasks without internal rejection, and is fulfilled with given tasks's fulfilled values. Note that this new task will be fulfilled with empty value-array, even though all tasks are rejected.
- SwiftTask（Promise拡張）を使う - Qiita (Japanese, ver 1.0.0)