我正在发现组合。我编写了以“组合”方式发出 HTTP 请求的方法,例如:
func testRawDataTaskPublisher(for url: URL) -> AnyPublisher<Data, Error> {
var request = URLRequest(url: url,
cachePolicy: .useProtocolCachePolicy,
timeoutInterval: 15)
request.httpMethod = "GET"
return urlSession.dataTaskPublisher(for: request)
.tryMap {
return $0.data
}
.eraseToAnyPublisher()
}
我想多次调用该方法并毕竟完成一项任务,例如:
let myURLs: [URL] = ...
for url in myURLs {
let cancellable = testRawDataTaskPublisher(for: url)
.sink(receiveCompletion: { _ in }) { data in
// save the data...
}
}
上面的代码不起作用,因为我必须将可取消项存储在属于该类的变量中。
第一个问题是:将许多(例如 1000)个可取消项存储在类似的内容中是一个好主意吗?Set<AnyCancellable>
???不会造成内存泄漏吗?
var cancellables = Set<AnyCancellable>()
...
let cancellable = ...
cancellables.insert(cancellable) // ???
第二个问题是:当所有可取消的任务都完成后,如何开始任务?我在想类似的事情
class Test {
var cancellables = Set<AnyCancellable>()
func run() {
// show a loader
let cancellable = runDownloads()
.receive(on: RunLoop.main)
.sink(receiveCompletion: { _ in }) { _ in
// hide the loader
}
cancellables.insert(cancellable)
}
func runDownloads() -> AnyPublisher<Bool, Error> {
let myURLs: [URL] = ...
return Future<Bool, Error> { promise in
let numberOfURLs = myURLS.count
var numberOfFinishedTasks = 0
for url in myURLs {
let cancellable = testRawDataTaskPublisher(for: url)
.sink(receiveCompletion: { _ in }) { data in
// save the data...
numberOfFinishedTasks += 1
if numberOfFinishedTasks >= numberOfURLs {
promise(.success(true))
}
}
cancellables.insert(cancellable)
}
}.eraseToAnyPublisher()
}
func testRawDataTaskPublisher(for url: URL) -> AnyPublisher<Data, Error> {
...
}
}
通常我会使用DispatchGroup
,启动多个HTTP任务并在任务完成时使用通知,但我想知道如何使用Combine以现代方式编写它。