iOS

Using RACCommand and creating custom RACSignals in Objective C

April 20, 2018 Denis Kutlubaev 2 Comments

To bind some action to the button click one can use just a custom RACSignal. But then you have to add three more things in every case:
1. Disable button, while action is performing;
2. Show, that action is in progress;
3. Disable button, if input is incorrect and button should not be able to be tapped.

Instead, if you use RACCommand, you get all these things in a box.

Let’s say, we want to bind RACCommand verifyPhoneCommand to a button. We can create a command in a lazy property in a ViewModel:

- (RACCommand *)verifyPhoneCommand
{
    if (! _verifyPhoneCommand) {
        _verifyPhoneCommand = [[RACCommand alloc] initWithEnabled:self.phoneValidSignal
                                                      signalBlock:^RACSignal * _Nonnull(id  _Nullable input) {
                                                          return [self verifyPhone];
                                                      }];
    }
    return _verifyPhoneCommand;
}

- (RACCommand *)verifyPhoneCommand

{

if (! _verifyPhoneCommand) {

_verifyPhoneCommand = [[RACCommand alloc] initWithEnabled:self.phoneValidSignal

signalBlock:^RACSignal * _Nonnull(id _Nullable input) {

return [self verifyPhone];

}];

}

return _verifyPhoneCommand;

}

Here phoneValidSignal is this signal, that is formed by observing a phone variable:

- (RACSignal *)phoneValidSignal
{
    if (!_phoneValidSignal) {
        _phoneValidSignal = [RACObserve(self, phone) map:^id(NSString *phone) {
            return @(phone.length > 0);
        }];
    }
    return _phoneValidSignal;
}

- (RACSignal *)phoneValidSignal

{

if (!_phoneValidSignal) {

_phoneValidSignal = [RACObserve(self, phone) map:^id(NSString *phone) {

return @(phone.length > 0);

}];

}

return _phoneValidSignal;

}

We pass a RACSignal verifyPhone to the RACCommand to do a job:

- (RACSignal *)verifyPhone
{
    return [RACSignal createSignal:^RACDisposable * _Nullable(id<RACSubscriber>  _Nonnull subscriber) {

        [[PhoneManager sharedManager]
         requestVerifyPhone:self.phone
         success:^{

             [subscriber sendNext:@(YES)];
             [subscriber sendCompleted];
             
         } failure:^(NSError *error) {
             
             [subscriber sendError:error];
             
         }];
        
        return nil;
    }];
}

- (RACSignal *)verifyPhone

{

return [RACSignal createSignal:^RACDisposable * _Nullable(id<RACSubscriber> _Nonnull subscriber) {

[[PhoneManager sharedManager]

requestVerifyPhone:self.phone

success:^{

[subscriber sendNext:@(YES)];

[subscriber sendCompleted];

} failure:^(NSError *error) {

[subscriber sendError:error];

}];

return nil;

}];

}

This is how we bind a RACCommand to a button:

self.smsRequestButton.rac_command = self.viewModel.verifyPhoneCommand;

1	self.smsRequestButton.rac_command = self.viewModel.verifyPhoneCommand;

To track execution of a RACCommand and show an activity indicator we can use executing property:

[self.viewModel.verifyPhoneCommand.executing subscribeNext:^(NSNumber*  _Nullable x) {
        if (x.boolValue) {
            [self.spinnerView startAnimating];
        }
        else {
            [self.spinnerView stopAnimating];
        }
    }];

[self.viewModel.verifyPhoneCommand.executing subscribeNext:^(NSNumber* _Nullable x) {

if (x.boolValue) {

[self.spinnerView startAnimating];

}

else {

[self.spinnerView stopAnimating];

}

}];

If errors happen during RACCommand execution we can process those errors:

[self.viewModel.verifyPhoneCommand.errors subscribeNext:^(NSError * _Nullable error) {
        [ErrorUtil showError:error from:self onRepeat:^{
            
        }];
    }];

[self.viewModel.verifyPhoneCommand.errors subscribeNext:^(NSError * _Nullable error) {

[ErrorUtil showError:error from:self onRepeat:^{

}];

iOS

Asynchronous requests chaining using FlatMap operator in RxSwift

April 14, 2018 Denis Kutlubaev Leave a comment

One of the main features of using RxSwift and RxCocoa or FRP is the possibility to chain several asynchronous requests and avoid callback hell. It can be achieved by using FlatMap operator and creating your own Observables from your asynchronous jobs like network requests or heavy calculations. But sometimes it is not simple to understand, how to do it. In this post I would like to show an example from one of my projects. The same can be applied to Objective C + ReactiveCocoa, the idea is the same.

First of all we should create Observables from different asynchronous requests. Then we can chain them using FlatMap operator. My example concerns a classic case – login and profile fetching. In many apps after logging in a user you have to request his profile in a separate request.

Usually you use MVVM with RxSwift. In a ViewModel you can create observables. In my case login() method creates an Observable from Alamofire request. In loadProfile() method Observable is created from ProfileService.

/// Logins user and saves credentials
///
/// - Returns: true if login was successfull; error in other cases
func login() -> Observable<Bool> {
    
    return Observable<Bool>.create { (observer) -> Disposable in
        
        let params = ["username": self.nameText.value,
                      "password": self.passwordText.value]
        
        self.inProgress.value = true
        
        Alamofire.request(APPURL.Login,
                          method: .post,
                          parameters: params)
            .responseJSON(completionHandler: { (dataResponse) in
                
                self.inProgress.value = false
                
                switch dataResponse.result {
                case .success(let value):
                    
                    guard let jsonDictionary = value as? Dictionary<String, Any> else {
                        let userInfo: [String : Any] =
                            [NSLocalizedDescriptionKey : "Unable to login with the provided credentials"]
                        let error = NSError(domain:"", code:0, userInfo:userInfo)
                        return observer.onError(error)
                    }
                    
                    guard let authToken = jsonDictionary["auth_token"] as? String else {
                        let userInfo: [String : Any] =
                            [NSLocalizedDescriptionKey : "Unable to login with the provided credentials"]
                        let error = NSError(domain:"", code:0, userInfo:userInfo)
                        return observer.onError(error)
                    }
                    
                    self.saveAuthToken(authToken)
                    
                    observer.onNext(true)
                    observer.onCompleted()
                    
                case .failure(let error):
                    
                    print("Could not login due to \(error)")
                    observer.onError(error)
                    
                }
            })
        
        return Disposables.create()
    }
}

/// Loads profile
///
/// - Returns: profile object if success, otherwise error
func loadProfile() -> Observable<Profile> {

    return Observable<Profile>.create({ (observer) -> Disposable in
        
        self.inProgress.value = true
        
        ProfileService.shared.getProfile {
            
            self.inProgress.value = false
            
            guard let profile = ProfileService.shared.profile else {
                let userInfo: [String : Any] =
                    [NSLocalizedDescriptionKey : "Unable to load profile"]
                let error = NSError(domain:"", code:0, userInfo:userInfo)
                return observer.onError(error)
            }
            
            observer.onNext(profile)
            observer.onCompleted()
        }
        
        return Disposables.create()
    })
}

/// Logins user and saves credentials

///

/// - Returns: true if login was successfull; error in other cases

func login() -> Observable<Bool> {

return Observable<Bool>.create { (observer) -> Disposable in

let params = ["username": self.nameText.value,

"password": self.passwordText.value]

self.inProgress.value = true

Alamofire.request(APPURL.Login,

method: .post,

parameters: params)

.responseJSON(completionHandler: { (dataResponse) in

self.inProgress.value = false

switch dataResponse.result {

case .success(let value):

guard let jsonDictionary = value as? Dictionary<String, Any> else {

let userInfo: [String : Any] =

[NSLocalizedDescriptionKey : "Unable to login with the provided credentials"]

let error = NSError(domain:"", code:0, userInfo:userInfo)

return observer.onError(error)

}

guard let authToken = jsonDictionary["auth_token"] as? String else {

let userInfo: [String : Any] =

[NSLocalizedDescriptionKey : "Unable to login with the provided credentials"]

let error = NSError(domain:"", code:0, userInfo:userInfo)

return observer.onError(error)

}

self.saveAuthToken(authToken)

observer.onNext(true)

observer.onCompleted()

case .failure(let error):

print("Could not login due to \(error)")

observer.onError(error)

}

})

return Disposables.create()

}

/// Loads profile

///

/// - Returns: profile object if success, otherwise error

func loadProfile() -> Observable<Profile> {

return Observable<Profile>.create({ (observer) -> Disposable in

self.inProgress.value = true

ProfileService.shared.getProfile {

self.inProgress.value = false

guard let profile = ProfileService.shared.profile else {

let userInfo: [String : Any] =

[NSLocalizedDescriptionKey : "Unable to load profile"]

let error = NSError(domain:"", code:0, userInfo:userInfo)

return observer.onError(error)

}

observer.onNext(profile)

observer.onCompleted()

}

return Disposables.create()

})

}

This is how you chain login and loadProfile requests. When they finish, you can do some job with a result profile. In this case I check a trial period and navigate to one of the views depending on a result.

@IBAction func signMeInAction(_ sender: AnyObject) {
    self.viewModel.login()
    .flatMap {result in
        self.viewModel.loadProfile()
    }
    .subscribe(onNext: { profile in
        let trialNotExpired = self.viewModel.checkTrialNotExpired(for: profile)
        if trialNotExpired {
            let firstAppLaunch = self.viewModel.checkFirstAppLaunch()
            if firstAppLaunch {
                self.performSegue(withIdentifier: Segue.FromLoginToInstruction, sender: nil)
            }
            else {
                self.navigationController?.popToRootViewController(animated: true)
            }
        }
        else {
            self.showTrialExpirePopUp()
        }
    },
    onError: { error in
        SCLAlertView().showError("Error", subTitle:error.localizedDescription)
    })
    .disposed(by: disposeBag)
}

@IBAction func signMeInAction(_ sender: AnyObject) {

self.viewModel.login()

.flatMap {result in

self.viewModel.loadProfile()

}

.subscribe(onNext: { profile in

let trialNotExpired = self.viewModel.checkTrialNotExpired(for: profile)

if trialNotExpired {

let firstAppLaunch = self.viewModel.checkFirstAppLaunch()

if firstAppLaunch {

self.performSegue(withIdentifier: Segue.FromLoginToInstruction, sender: nil)

}

else {

self.navigationController?.popToRootViewController(animated: true)

}

else {

self.showTrialExpirePopUp()

}

onError: { error in

SCLAlertView().showError("Error", subTitle:error.localizedDescription)

})

.disposed(by: disposeBag)

}

Note that error for both requests is handled in one place using SCLAlertView. FlatMap operator maps a result of a first request to a second request and also flattens Observables. If you use just Map instead of FlatMap, the result of chaining will be an Observable of Observables.

iOS

Loading a TableFooterView that uses Autolayout from XIB

April 2, 2018 Denis Kutlubaev Leave a comment

You can use Autolayout and Xibs to create a footer view. But you have to put your custom view to the container view, that you assign to tableFooterView. If you use Autolayout and load Header or Footer View from xib, you should add constraints.

func setupTableFooterView() {
    // Create your footer view from XIB and set constraints (in my case it is historyToolBarView of class HistoryToolBarView)
    let view = Bundle.main.loadNibNamed("HistoryToolBarView", owner: self, options: nil)?.first
    historyToolBarView = view as! HistoryToolBarView
    historyToolBarView.translatesAutoresizingMaskIntoConstraints = false
    historyToolBarView.addConstraints(
        [NSLayoutConstraint.init(item: self.historyToolBarView,
                                 attribute: .height,
                                 relatedBy: .equal,
                                 toItem: nil,
                                 attribute: .notAnAttribute,
                                 multiplier: 1.0,
                                 constant: 60),
         NSLayoutConstraint.init(item: self.historyToolBarView,
                                 attribute: .width,
                                 relatedBy: .equal,
                                 toItem: nil,
                                 attribute: .notAnAttribute,
                                 multiplier: 1.0,
                                 constant: UIScreen.main.bounds.size.width)])
    
    // Create a container of your footer view called footerView and set it as a tableFooterView
    let footerView = UIView(frame: CGRect.init(x: 0, y: 0, width: tableView.frame.width, height: 60))
    footerView.backgroundColor = UIColor.green
    tableView.tableFooterView = footerView
    
    // Add your footer view to the container
    footerView.addSubview(historyToolBarView)
}

func setupTableFooterView() {

// Create your footer view from XIB and set constraints (in my case it is historyToolBarView of class HistoryToolBarView)

let view = Bundle.main.loadNibNamed("HistoryToolBarView", owner: self, options: nil)?.first

historyToolBarView = view as! HistoryToolBarView

historyToolBarView.translatesAutoresizingMaskIntoConstraints = false

historyToolBarView.addConstraints(

[NSLayoutConstraint.init(item: self.historyToolBarView,

attribute: .height,

relatedBy: .equal,

toItem: nil,

attribute: .notAnAttribute,

multiplier: 1.0,

constant: 60),

NSLayoutConstraint.init(item: self.historyToolBarView,

attribute: .width,

relatedBy: .equal,

toItem: nil,

attribute: .notAnAttribute,

multiplier: 1.0,

constant: UIScreen.main.bounds.size.width)])

// Create a container of your footer view called footerView and set it as a tableFooterView

let footerView = UIView(frame: CGRect.init(x: 0, y: 0, width: tableView.frame.width, height: 60))

footerView.backgroundColor = UIColor.green

tableView.tableFooterView = footerView

// Add your footer view to the container

footerView.addSubview(historyToolBarView)

}

Alwawee

Monthly Archives: April 2018

Using RACCommand and creating custom RACSignals in Objective C

Asynchronous requests chaining using FlatMap operator in RxSwift

Loading a TableFooterView that uses Autolayout from XIB

iOS Development