I would like to know, according to a job interview that I have been, how to fetch 2 differents API call - let say movie name and international language support API
how to download 2 of them together to into one table view?
thank you in advance it will help me a lot
It is Simple You have to create request chain and after getting both result reload the tableview
you have create array of dictionary from both service resposnse
For example say first will return just arrayForMovieName:["a","b","c"]
and Second will return just arrayForLanguage:["Hindi","English","etc"]
now merge this two array into your created third array of dictionary like
arrForMovieWithLanguage = [[movie:"a","language":["Hindi","English"]],[movie:"b","language":["English"]]]
Solution :1 Take boolean for both service like
var isLanguageGet:Bool = false
var isMovieGet:Bool = false
wsGetMovie()
{
isMovieGet = true
if isLanguageGet
{ self.tableView.reloadData()
}
}
wsGetLanguage()
{
isLanguageGet = true
if isMovieGet
{ self.tableView.reloadData()
}
}
Solution :2 Make webservice call sync
wsGetMovie()
{
wsGetLanguage()
}
wsGetLanguage()
{
self.tableView.reloadData()
}
You can use closure to wait asynchronously for another API response. i 'm just give you a idea of implementation. after that you can implement as per your requirement.
In my requirement it needs Euro price from first service. and after that another API need that euro price and will return Payment data. So, I achieve this scenario like below.
func getPaymentDetail(euroPrice: Double, completion: #escaping (Result<JSON>) -> Void) {
// Call second API and return result in completion closure.
if response.result.isSuccess {
completion(response.result)
}
// For failure handle here.
}
func getPriceOfEuro(rate: #escaping (Double) -> Void) {
// Here I get Euro price.
}
Then bind them in sequence like below.
getPriceOfEuro(rate: { (price) in
self.getPaymentDetail(euroPrice: price, completion: { (result) in
// Take data from result and reload Table.
})
})
Related
I'm attempting to use Vapor3 to perform raw SQL queries. The supplied documentation for this kind of thing is pretty vague on the website unfortunately.
Essentially I want to do something like:
router.get("example") { req -> Future<View> in
let leaf = try request.make(LeafRenderer.self)
// I can't get this next bit to work. Does anyone have any ideas how to do this? I seem to get all sorts of Xcode errors with .mysql, closures etc.
let users = try request.withNewConnection(to: .mysql) { connection -> EventLoopFuture<[User]>
return try connection.raw("select * from users").all(decoding: User.self)
}
var context = [String: String]()
context["user"] = users
return leaf.render("example", context)
}
Any help on want I'm doing wrong here would be greatly appreciated.
Thanks in advance,
Matt
You code was failing because you aren't implementing the closure properly. Your route returns in the let users... closure so the second return is never reached.
This works:
router.get("example")
{
insecure.get("example") {
request -> Future<View> in
return request.withNewConnection(to: .mysql) {
connection in
return connection.raw("select * from User").all(decoding: User.self).flatMap(to:View.self) {
users in
return try request.make(LeafRenderer.self).render("example",["users":users])
}
}
}
}
The changes are:
There's no need to define leaf until you need it.
The definition of users is now inside the closure.
I'm confused on how to query the children of a model object and use it immediately. My Client contains a number of Station children
final class Client: PostgreSQLModel {
var stations: Children<Client, Station> {
return children(\.clientID)
}
}
and then in my controller I have a list of clients that I want to look at and grab their stations.
func clientIndexHandler(_ req: Request) throws -> Future<View> {
return Client.query(on: req).all().flatMap(to: View.self) { clients in
let sorted = clients.sorted { ... }
let content = try sorted.map { client in
let stations = try client.stations
.query(on: req)
.all()
.map(to: [String].self) { stations in
return stations.map { $0.name }
}
// Now I want to use the stations for other stuff.
return ClientIndexContent(client: client, stations: stations, ....)
}
let context = ClientIndexContext(clients: content)
return try req.make(LeafRenderer.self).render("clients/index", context)
}
}
My problem is that stations is an EventLoopFuture<[String]> instead of a [String]. Since I'm using Leaf here I need the actual values from the clients and stations so that I can populate the content to pass into the leaf renderer.
So you have a number of ways of doing it, but basically you need to rethink how you do things in an async world. However, Vapor does provide some nice things to help this. To start with, Leaf can actually handle futures, so if you set your ClientIndexContext to have a property of let stations: Future<[String]>, then you can just access that inside Leaf as normal.
The other option you can do is to call map(to: [String].self) on stations which will get all of the futures for you.
obviously I am new to RxSwift and though I consumed a lot of documentations and speeches, I think I am missing some fundamental concepts.
In my app I have a RESTful web service to load various resources but the base url of the web service is unknown at build/start time. Instead I have a "URL resolver" web service which I can call with my apps bundle, version and possible environment ("production", "debug" or any custom string entered in the apps debug settings) to obtain the base url I then use for the actual service.
My thinking was that I would create 2 services, one for the URL resolver and one for the actual web service which gives me my resources. The URL resolver would have a Variable and a Observable. I use the variable to signal the need to refresh the base url via a web service call to the URL resolver. I do this by observing the variable and filter only for true values. A function in the service class set the variables value to true (initially it is false) and inside an observer of the filtered variable, I make the web service call in another Observable (this example uses a dummy JSON web service):
import Foundation
import RxSwift
import Alamofire
struct BaseURL: Codable {
let title: String
}
struct URLService {
private static var counter = 0
private static let urlVariable: Variable<Bool> = Variable(false)
static let urlObservable: Observable<BaseURL> = urlVariable.asObservable()
.filter { counter += 1; return $0 }
.flatMap { _ in
return Observable.create { observer in
let url = counter < 5 ? "https://jsonplaceholder.typicode.com/posts" : ""
let requestReference = Alamofire.request(url).responseJSON { response in
do {
let items = try JSONDecoder().decode([BaseURL].self, from: response.data!)
observer.onNext(items[0])
} catch {
observer.onError(error)
}
}
return Disposables.create() {
requestReference.cancel()
}
}
}
static func getBaseUrl() {
urlVariable.value = true;
}
static func reset() {
counter = 0;
}
}
Now the problem is that sometimes it can happen that a web service call fails and I would need to show the error to the user so a retry can be made. I thought that the onError was useful for this but it seems to kills all the subscribers forever.
I could put the subscribing in its own function and inside the error handler of the Observer, I could show a alert and then call the subscribe function again like so:
func subscribe() {
URLService.urlObservable.subscribe(onNext: { (baseURL) in
let alert = UIAlertController(title: "Success in Web Service", message: "Base URL is \(baseURL.title)", preferredStyle: .alert)
let actionYes = UIAlertAction(title: "Try again!", style: .default, handler: { action in
URLService.getBaseUrl()
})
alert.addAction(actionYes)
DispatchQueue.main.async {
let alertWindow = UIWindow(frame: UIScreen.main.bounds)
alertWindow.rootViewController = UIViewController()
alertWindow.windowLevel = UIWindowLevelAlert + 1;
alertWindow.makeKeyAndVisible()
alertWindow.rootViewController?.present(alert, animated: true, completion: nil)
}
}, onError: { error in
let alert = UIAlertController(title: "Error in Web Service", message: "Something went wrong: \(error.localizedDescription)", preferredStyle: .alert)
let actionYes = UIAlertAction(title: "Yes", style: .default, handler: { action in
URLService.reset()
self.subscribe()
})
alert.addAction(actionYes)
DispatchQueue.main.async {
VesselService.reset()
let alertWindow = UIWindow(frame: UIScreen.main.bounds)
alertWindow.rootViewController = UIViewController()
alertWindow.windowLevel = UIWindowLevelAlert + 1;
alertWindow.makeKeyAndVisible()
alertWindow.rootViewController?.present(alert, animated: true, completion: nil)
}
}).disposed(by: disposeBag)
}
Then in my AppDelegate I would call
subscribe()
URLService.getBaseUrl()
The problem is that all other observers get killed on an error as well but since the the only other observer on the URLService.urlObservable is my other web service class, I guess I could implement the same style subscribe function in there as well.
I read that some people suggest to return a Result enum which has 2 cases: the actual result (.success(result: T)) or an error (.error(error: Error)).
So what is the better way of handling errors web service errors in Rx? I cant wrap my head around this problem and I'm trying for 2 days to understand it. Any ideas or suggestions?
Update
It just came to my mind that I could ignore errors from the web service calls completely and instead post any error to a global "error" variable which my app delegate could observe to show alerts. The "error" could reference the function which initially caused it so a retry could be made. I'm still confused and not sure what I should do. :/
Update 2
I think I might found a working solution. As I am still a beginner to Rx and RxSwift, I'm happy to take improvement suggestions. As I was writing the actual code, I splitted my call chain in two parts:
The part where I make the web service calls
The part where I click a button and process the result of the web service, whether it is an error or a success
In the part where I click the button and process the result, I use catchError and retry as suggested in the comments. The code looks like this:
let userObservable = URLService
.getBaseUrl(environment: UserDefaults.standard.environment) //Get base url from web service 1
.flatMap({ [unowned self] baseURL -> Observable<User> in
UserService.getUser(baseURL: baseURL,
email: self.usernameTextField.text!,
password: self.passwordTextField.text!) //Get user from web service 2 using the base url from webservice 1
})
signInButton
.rx
.tap
.throttle(0.5, scheduler: MainScheduler.instance)
.flatMap({ [unowned self] () -> Observable<()> in
Observable.create { observable in
let hud = MBProgressHUD.present(withTitle: "Signing in...");
self.hud = hud
observable.onNext(())
return Disposables.create {
hud?.dismiss()
}
}
})
.flatMap({ () -> Observable<User> in
return userObservable
})
.catchError({ [unowned self] error -> Observable<User> in
self.hud?.dismiss()
self.handleError(error)
return userObservable
})
.retry()
.subscribe(onNext: { [unowned self] (user) in
UserDefaults.standard.accessToken = user.accessToken
UserDefaults.standard.tokenType = user.tokenType
self.hud?.dismiss()
})
.disposed(by: disposeBag)
The trick was to move the call to the two web services out of the cain into their own variable so I can re-call it at any time. When I now return the "userObservable" and an error happens during the web service call, I can show the error in the catchError and return the same "userObservable" for the next retry.
At the moment this only properly handles errors when they occur in the web service call chain so I think I should make the button tap a driver.
Okay so for everyone who comes here, you probably have a lack of understanding or a misconception of how the Rx world is supposed to work. I still find it sometimes confusing but I found a way better solution than what I posted in my original question.
In Rx, a error "kills" or rather completes all observers in the chain and that is actually a good thing. If there are expected errors like API error in web service calls, you should either try to handle them where they occur or treat them like expected values.
For example, your observer could return a optional type and subscribers could filter for the existence of values. If an error in the API call occurs, return nil. Other "error handlers" could filter for nil values to display error messages to the user.
Also viable is to return a Result enum with two cases: .success(value: T) and .error(error: Error). You treat the error as a acceptable result and the observer is responsible for checking if it should display a error message or the success result value.
Yet another option, which surely is not the best as well but works it to simply nest the call which you expect to fail inside the subscriber of the call which must not be affected. In my case that is a button tap which causes a call to a web service.
The "Update 2" of my original post would become:
signInButton.rx.tap.throttle(0.5, scheduler: MainScheduler.instance)
.subscribe(onNext: { [unowned self] () in
log.debug("Trying to sign user in. Presenting HUD")
self.hud = MBProgressHUD.present(withTitle: "Signing in...");
self.viewModel.signIn()
.subscribe(onNext: { [unowned self] user in
log.debug("User signed in successfully. Dismissing HUD")
self.hud?.dismiss()
}, onError: { [unowned self] error in
log.error("Failed to sign user in. Dismissing HUD and presenting error: \(error)")
self.hud?.dismiss()
self.handleError(error)
}).disposed(by: self.disposeBag)
}).disposed(by: self.disposeBag)
The MVVM view model makes the calls to the web serivces like so:
func signIn() -> Observable<User> {
log.debug("HUD presented. Loading BaseURL to sign in User")
return URLService.getBaseUrl(environment: UserDefaults.standard.environment)
.flatMap { [unowned self] baseURL -> Observable<BaseURL> in
log.debug("BaseURL loaded. Checking if special env is used.")
if let specialEnv = baseURL.users[self.username.value] {
log.debug("Special env is used. Reloading BaseURL")
UserDefaults.standard.environment = specialEnv
return URLService.getBaseUrl(environment: specialEnv)
} else {
log.debug("Current env is used. Returning BaseURL")
return Observable.just(baseURL)
}
}
.flatMap { [unowned self] baseURL -> Observable<User> in
log.debug("BaseURL to use is: \(baseURL.url). Now signing in User.")
let getUser = UserService.getUser(baseURL: baseURL.url, email: self.username.value, password: self.password.value).share()
getUser.subscribe(onError: { error in
UserDefaults.standard.environment = nil
}).disposed(by: self.disposeBag)
return getUser
}
.map{ user in
UserDefaults.standard.accessToken = user.accessToken
UserDefaults.standard.tokenType = user.tokenType
return user
}
}
First I was thinking to only call the view models signIn() function when pressing the button but since there should be no UI code in the view model, I figured that presenting and dismissing the HUD is the responsibility of the ViewController.
I think this design is now pretty solid. The button observer never completes and can continue to send events forever. Earlier, if there was a second error, it might happen that the button observer died and my logs showed that the userObservable was executed twice, which must also not be happen.
I just wonder if there is a better way then nesting the subscribers.
I want to implement UISearchContoller that search from webservice JSON with swifty json, exactly like apple's appStore when you search for an app, it loads without load them into tableView
here is what I have done in updateSearchResultsForSearchController method:
func updateSearchResultsForSearchController(searchController: UISearchController) {
filterContentForSearchText(searchController.searchBar.text!)
}
func filterContentForSearchText(searchText: String) {
filteredContents = myStruct.filter{$0.name.rangeOfString(searchText) != nil
}
Posting more of your code would be nice, like what you are using to get the results from the web service, However, I will try to step you through it anyway.
I have done with before just using a UISearchBar and it's delegate method, one the user pressed the search button or enter, I would use NSURLSession to pass the user's search terms to the API, and parsed the response.
func searchBarSearchButtonClicked(_ searchBar: UISearchBar) {
let searchText : String = searchBar.text
webService.getRecipe(ingredient: searchText, completionHandler: { (recipeArray) in
self.highProteinArray = recipeArray
dispatch_async(dispatch_get_main_queue(), {
self.collectionView.reloadData()
})
})
}
As you can see I used a callback to handle setting the newly parsed data to a variable for later use, and then reloaded the collectionView. This way your tableView/collectionView will load and set itself up while you are waiting for the response from the web service and then parsing it, once that is complete you just reload to show the new data.
To add a little extra you could even add a fading in animation in your cellForItemAtIndexPath or cellForRowAtIndexPath, whichever you are using.
I've just started learning Rust, and have come from a mainly JavaScript background so I'm a bit stumped when it comes to the whole borrowing system and memory management.
I have the following code:
fn load(db: &MyPool, id: i32) -> &Account{
let accounts: Vec<Account> = db.prepare("SELECT id, balance, name FROM `accounts` WHERE `id`=?")
.and_then(|mut stmt| {
stmt.execute(&[&id]).map(|result| {
result.map(|x| x.unwrap()).map(|row| {
Account{
id: from_value(&row[0]),
balance: from_value(&row[1]),
name: from_value(&row[2])
}
}).collect()
})
}).unwrap();
&accounts[0]
}
And I've managed to fix all the errors the compiler throws out apart from
/main.rs:42:4: 42:12 error: 'accounts' does not live long enough
Is this the best way to get one result from the MySQL query, or have I been going at it completely wrong?
You don't want to return a reference to an account, but you want to pass ownership to the caller after retrieving from the db.
Thus, change the signature to:
fn load(db: &MyPool, id: i32) -> Account
Now the idea would be to return the object by value, not by reference:
accounts[0]
However doing so will fail with an error: cannot move out of indexed content. A better approach would be to avoid collecting in a vector altogether, and use Iterator::next(&self) to take the first element. This would look like:
fn load(db: &MyPool, id: i32) -> Account{
let account: Account = db.prepare("SELECT id, balance, name FROM `accounts` WHERE `id`=?")
.and_then(|mut stmt| {
stmt.execute(&[&id]).map(|result| {
result.map(|x| x.unwrap()).map(|row| {
Account{
id: from_value(&row[0]),
balance: from_value(&row[1]),
name: from_value(&row[2])
}
}).next().unwrap() // <- next() takes the first elt of the iterator
})
}).unwrap();
account // <- return by value, pass ownership to caller
}
(Untested as I couldn't reproduce your dev environment.)
Kind of unrelated, but it is worth noting that those multiple unwrap() calls render your function extremely brittle as any failure will crash your whole program with a panic. Fortunately the answer to this bad smell is easy: you want to return Option<Account> rather than Account. Then remove all calls to unwrap() and let the Option<Account> propagate throughout calls (your use of map() is good because it says "return None if you find None and return Some(f(a)) if you find Some(a)".)