Category Archives: iOS

How to load profile info

Declare the header file for EpamAuth:

Then declare a property that conforms to the Authorization interface.

Then initialize the property in init or a lazyloading accessor

Finally, use it like this:

If its your first time logging in, you will have a login window appear. Sign in using your EPAM credentials.

If you have previously logged in, your authentication token will be saved in the keychain, and you don’t have to log in a second time. You simply will be automatically logged in.

To log out:

Adding and Removing Observer in UIView

ref –

In your UIView custom class:

Converting existing Project to read from Azure Backend

Import Data Model

File >> New >> File >> Data Model. Name it “Activities”.

Ctrl + click >> Show in Finder. Then drag that file onto a text editor such as sublime. You will see basic xml file.

Drag and drop an existing data model file onto the text editor. Copy and paste all the content into your Activities file. Save and close. Your data model should be now updated. Your iOS data model is ready.

Basic Core Stack Class

Create a basic core data stack class with a context, MOC, and PSC.
Make sure the your sql file name, and the data model name are specified.

core data demo

#define DATA_MODEL_FILENAME @”Activities”
#define SQL_FILENAME @”Activities.sqlite”


Azure should generate a QSTodoService object that does all the reading and writing of data for you.

Unfortunately, it also generates core data code that sits in your AppDelegate. Pull all the core data code out onto your own CoreDataStack class so that AppDelegate is clean.

Then, make these modifications to your QSTodoService:

Use your core stack and its context in QSTodoService’s init method. Commented out code is the original.


conform to NSFetchedResultsControllerDelegate protocol

specify what/how you want to fetch for the fetchedResultsController

In the viewDidLoad, make sure you create your QSTodoService because we are going to implement a refresh method that uses it to sync all the data between your app the backend service.

use the fetchedResultsController to get the objects

Programmatically add a Navigation Controller to your project

objective C demo
swift 3 demo






The whole idea is that your window strongs UINavigationController, and UINavigationController strongs your main ViewController.

The UINavigationController is set up in your AppDelegate. Then your UINavigationController is init-ed with your main view controller.


Then, in your main view controller, use self.navigationItem to set up the buttons and title.



First we create a UINavigationController property.

Then, we create the UINavigationController and init it with the main view controller of your project.
Set the UINavigationController as the root view controller of our window.

In your main view controller, make sure in your viewDidLoad, you set the navigation button like so:

The nav button has a button responder:

This means when you click on the nav button, we want to navigate to a new view controller. Hence, let’s implement the view controller that we want to navigate to.

File >> New >> File >> Cocoa Touch Class

Put in AddViewController for the “class name”.
Put in UIViewController for the “subclass of”.

Then import AddViewController to your main view controller, and implement the button responder like so:

Make sure you set background color for every view controller because if its default as clear, there may be animation issues.

NSURLSession – Out of process upload/download

ref –

demo project

Background Uploads and Downloads

Adding support for background uploads and downloads is surprisingly easy with NSURLSession. Apple refers to them as out-of-process uploads and downloads as the tasks are managed by a background daemon, not your application. Even if your application crashes during an upload or download task, the task continues in the background.

Enabling background uploads and downloads is nothing more than flipping a switch in your session’s configuration. With a properly configured session object, you are ready to schedule upload and download tasks in the background.

When an upload or download is initiated:

  1. background daemon comes into existence
  2. The daemon takes care of the task and sends updates to the application through the delegate protocols declared in the NSURLSession API
  3. If app stops, daemon continues task
  4. If download task finishes, daemon informs session.
  5. The session then invokes the appropriate delegate methods to make sure your application can take the appropriate actions, such as moving the file to a more permanent location.

When the Background Transfer Service gets in action, what is actually happening is that the operating system takes charge of all the download process, performing everything in background threads (daemons).

While a download is in progress, delegates are used to inform the app for the progress, and wakes it up in the background to get more data if needed, such as credentials for logging in to a service. However, even though everything is controlled by the system, users can cancel all downloads at any time through the application.

A reminder that a block parameter has 3 parts. The return, the parameter, and the block name. Like so:

So this means that the block is used where it takes 2 doubles, and does not return anything. It is called by using the block name ‘block’.

Handle Events for Background Session

Apps that (using an NSURLSession with a background configuration) may be launched or resumed in the background in order to handle the
completion of tasks in that session, or to handle authentication.

In other words, when an app uses NSURLSession with background service (whether its a GET request or downloading/uploading), NSURLSession needs to let the app know and to handle the completion of tasks for that session.

We simply strong the completionHandler block in order to call it later to let the system know that we complete all tasks.

NSURLSessionDelegate’s PROTOCOL METHOD will be called. In there you access the appDelegate and call the completionHandler.

Hence when you’re using it, if an application has received an -application:handleEventsForBackgroundURLSession:completionHandler:
message, the session delegate will receive this message to indicate
that all messages previously enqueued for this session have been

Declare the session completion handler member variable:


Then, have its set property copy the completion handler:


Go to your ViewController and conform to NSURLSessionDelegate.

This is so that we need to implement URLSessionDidFinishEventsForBackgroundURLSession.

Now when your session object’s delegate queue tasks have all been processed, in your AppDelegate, you will receive a
application has received an -application:handleEventsForBackgroundURLSession:completionHandler:
message and your protocol method

will be called.

Then your session delegate will send a message to protocol method URLSessionDidFinishEventsForBackgroundURLSession to indicate that all messages previously enqueued for this session have been

Hence that’s why its the job of your URLSessionDidFinishEventsForBackgroundURLSession method to simply call the completionHandler and clean it up.

If your session delegate sends a message to call protocol method:

for authentication purposes, then you need to something similar. Where you give authentication information, then call the completionHandler().

Prepare the UI

Configuration Object

Session Object

Updating download progress percentages

When you resume a download task

Send last message related to a specific task

When your download have completed