Working with Touch ID API in iOS 8 SDK

With every major version release of iOS, Apple ships along a great number of new technologies and frameworks. iOS 8 is going to be released officially pretty soon, and new great stuff awaits both users and developers. This version of iOS brings quite exciting new things, and among them, don’t forget the new programming language named Swift, that Apple presented at the WWDC this summer. So, with this tutorial I would like to welcome you to a series of new posts, in which we are going to work with frameworks introduced in iOS 8, and with improvements made to the existing SDK.

Starting from this tutorial, we are going to develop all the sample applications for the next ones in Swift. Not because it’s a brand new language and it would be cool to get to know it, but mostly because it’s quite possible to become the official language of iOS (and Mac OS) after a while. We have been working with Objective-C for some time, some of us for years, and of course, we don’t mean to forget it. However, as technology evolves, it’s our duty to learn this new language.

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Before I start talking about the topic of this tutorial, I would like to make a few observations regarding Swift, since this is the first time I write about it. I am pretty sure that all of you that you are now reading these lines, you have seen the related WWDC session videos, you have downloaded the e-book, and you’ve read a few (or more) things about Swift. Compared to Objective-C, Swift is much simpler from the point of syntax, the code is much clearer and of course, thanks to the nature of Swift, safer. Furthermore, one could say that reminds a combination of other languages. Even though it’s necessary to get used to a new way of writing code and to forget old habits (such as adding the semicolon ; at the end of each command), there are only a few new things you have to learn in Swift (such as optionals, tuples, new way to handle structures, etc.). If it has been easy for you to develop applications in Objective-C, then it’s really easy to write code in Swift too, and you will find this out through this tutorial. Closing this short talk about Swift, I must say that since this language is new, I recommend you to keep the e-book always open for study, and of course… to read the tutorials at Appcoda!
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Understanding Self Sizing Cells and Dynamic Type in iOS 8

In iOS 8, Apple introduces a new feature for UITableView known as Self Sizing Cells. To me, this is seriously one of the most exciting features for the new SDK. Prior to iOS 8, if you want to display dynamic content in table view with variable height, you would need to calculate the row height manually. Now with iOS 8, Self Sizing Cell provides a solution for displaying dynamic content. In brief, here are what you need to do when using self sizing cells:

  • Define auto layout constraints for your prototype cell
  • Specify the estimatedRowHeight of your table view
  • Set the rowHeight of your table view to UITableViewAutomaticDimension

If we express the last two points in code, it looks like this:

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tableView.estimatedRowHeight = 44.0
tableView.rowHeight = UITableViewAutomaticDimension

With just two lines of code, you instruct the table view to calculate the cell’s size matching its content and render it dynamically. This self sizing cell feature should save you tons of code and time. You’re gonna love it.

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Using Gesture Recognizers to Handle Pinch, Rotate, Pan, Swipe and Tap Gestures

Hello readers! iOS 8 is at the gates, as only a few weeks remain until the official release of the updated version of the operating system, and along with it, the release of the Swift programming language. So, as you understand, we are preparing to enter into a new era of the iOS SDK, where new wonderful technologies waiting for us to explore them! However, here at Appcoda we decided to dedicate one more tutorial to the existing SDK, using the Objective-C language. My next tutorials will focus on new iOS 8 technologies, and we’ll use the Swift language. Regarding this one, there were many candidate topics to write for, but ultimately the chosen one is about the Gesture Recognizers. So, let’s see a few things about them.

A gesture recognizer is actually an object of the abstract class UIGestureRecognizer. Such an object is related to a view, and monitors for predefined gestures made on that view. Going one level deeper, I would say that gestures are actually touches and movements of one or more fingers that happen on a specific area of the screen, where a view of interest exists there. In the early versions of iOS SDK, gestures recognizers were not provided to developers, so implementing such ways of interaction required a lot of manual work. Thankfully, Apple wrapped up all that manual work and gave it to developers as a single tool, and that way working with gestures became a really easy part of the iOS programming.

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Introduction to UIAlertController, Swift Closures and Enumeration

Among all the changes in iOS 8 SDK, the changes of two commonly-used APIs in UIKit framework are less known. Both UIActionSheet and UIAlertView classes are now replaced by the UIAlertController class.

In iOS 8, whenever you want to display an alert message in your app, you should use UIAlertController instead the two deprecated classes. The action sheet and alert view become the style of the UIAlertController. You choose one of the styles when creating an alert controller. The way to handle button action is redesigned. You no longer use delegate (e.g. UIAlertViewDelegate) to handle user response. When using UIAlertController, you associate actions with the controller and that the action is expressed as a block in Objective-C or closures in Swift.

In this tutorial, I’ll give you an introduction to the UIAlertController and cover how to use the class to present an alert message, as well as, an action sheet. On top of that, I’ll take this opportunity to cover the basics of closures and enumeration in Swift.

UIAlertController Introduction

Okay, let’s get started.
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Understanding Key-Value Observing and Coding

In programming, one of the most commonly accepted facts is that the flow of a program depends on the value of the various variables and properties you use. You just have to think how many times during an application development you have to check for your properties’ values, and based on them to drive the execution of the code to one or another way. Even more, think of how many times you need to check if an object has been added to an array, or if it has been removed from it. So, being aware of the changes that happen to the properties of your classes is a vital part of the programming process.

There are various ways that let us be notified when a property gets changed. For example, if you have a method to set a property’s value, or you just override a setter method, you can send a notification (NSNotification) to notify an observer about that change, and then perform the proper actions based on the value that was set. If you are familiarized with notifications, then using them would not be a problem at all if you would want to use them for being aware about changes in properties, but the truth is that doing so for a great number of properties would require to send and observe for a great number of notifications as well, and that could lead to a lot of extra code writing.

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Nevertheless, there is a much better way to observe for changes in properties, and Apple uses it a lot in its own software. That way is not used a lot by programmers because it seems hard to be learnt, however this is not true. Once you get to know it, you’ll probably love it and you’ll see that it’s much effortless and easier to track down changes on single properties or collections, such as arrays. This method is called Key-Value Observing, but is mostly known as KVO.

Key-Value Observing (KVO) is related directly to another powerful and important mechanism, named Key-Value Coding, or KVC. Actually, any property you want to observe for changes must be Key-Value Coding compliant, but we will talk more about that later. The important thing for now is to make clear that both of them provide a really powerful and efficient way to write code, and knowing how to handle them can definitely turn you into a more skilled and advanced programmer.
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Understanding XML and JSON Parsing in iOS Programming

One of the most important tasks that a developer has to deal with when creating applications is the data handing and manipulation. Data can be expressed in many different formats, and mastering at least the most known of them consists of a key ability for every single programmer. Speaking for mobile applications specifically now, it’s quite common nowadays for them to exchange data with web applications. In such cases, the way that data is expressed may vary, but usually is preferred either the JSON or the XML format.

iOS SDK provides classes for handling both of them. For managing JSON data, there is the NSJSONSerialization class. This one allows to easily convert a JSON data into a Foundation object (NSArray, NSDictionary), and the other way round. For parsing XML data, iOS offers the NSXMLParser class, which takes charge of doing all the hard work, and through some useful delegate methods gives us the tools we need for handling each step of the parsing.

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Introduction to Auto Layout

Editor’s note: If you’ve downloaded the Xcode 6 beta and played around with it, one thing you may notice is the change of Interface Builder. The default view controller is now wider and doesn’t look like an iPhone 5. When you position a button in the center of the view and run the app, it doesn’t look good. The button is not centered properly.

What’s wrong? How can you make it right? The answer is Auto Layout. Auto Layout is a constraint-based layout system. It allows developers to create an adaptive interface that responds appropriately to changes in screen size and device orientation. We seldom talk about Auto Layout in our tutorials. Some beginners find it hard to learn and avoid using it. Starting from Xcode 6, you should learn to love Auto Layout. Apple is expected to release 4.7-inch and 5.5-inch iPhone 6 this fall. Without using Auto Layout, it would be very hard for you to build an app that supports all screen sizes.

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So starting from this week, we’ll publish a series of articles about Auto Layout. We’ll start with the basics.

Enter the introduction of Auto Layout by Ziad.

I know that there are many developers who hates Auto Layout, maybe because it’s relatively new or it’s hard to use for the very first time. But believe me, once you get comfortable with it, it becomes one of your greatest tools that you can’t live without when developing your app. In this tutorial, I will give you a very brief introduction of Auto Layout.
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How to Access iOS Calendar, Events and Reminders Using Event Kit Framework

One of the not so well-known frameworks existing on iOS (and Mac OS), is the Event Kit framework. This framework has one purpose only, to let us access the calendars, the events and the reminders of a device, and work with them. If you have ever been wondered about how you can create custom events through your app, or how to set reminders without using the Reminders app, then the Event Kit is the answer you’re looking for. Through this tutorial, you will have the chance to meet it, as you’ll get to know the most important aspects of it.

Before we start working with it, I think it would be useful to mention a few facts about the Event Kit framework. What actually the framework does, is to provide access to the Calendar and Reminders apps, and make your own app capable of retrieving information, or adding new. Behind of both of these apps, there is the same database, named Calendar Database. What you can do with the framework is to create, edit and delete both events and reminders. Events are displayed in the Calendar app, while reminders are (obviously) displayed in the Reminders app. Further than that, you are given the ability to create or delete calendars, and furthermore, to perform more advanced tasks, such as settings alarms for an upcoming event or reminder, or making them recurring.

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When using the Event Kit framework, you should always have in mind that the user must grant access to either Calendar or Reminders apps. Upon the first launch of an app that uses the framework, an alert view asking for the user consent must appear, and it’s up to users to decide whether your app will be able to work with any of the above resources. After all, asking for user permissions is something that always happen in cases of frameworks that deal with other apps or resources of the iOS. Therefore, you should check if user has granted access, and then make the related to Event Kit features available.

As always, I recommend you to go through the Apple documentation as well for getting a greater level of understanding on the topic. Having said all that, let’s move on to make our introduction to the sample app of this tutorial.
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iOS Programming 101: Implementing Pull-to-Refresh and Handling Empty Table

In this iOS Programming 101 post, I would like to answer two common questions raised by our readers.

  1. I follow your table view tutorial to create my first app. The tutorial is great. It shows us how to display data in the table view. But what if the table is empty? When there is no data, the app should display a friendly message instead of just display empty rows. How can I do that?
  2. I like the pull-to-refresh gesture. It’s a great way for content update. How can I implement such feature in my table-based app?

    Let us first take a look at the first question and see how to display a text message when the table is empty. The UITableView class includes the backgroundView property, which is the background view of the table view. This property is set to nil by default. To display a message or an image when the table is empty, usually we configure this property and set it to our own view.

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How to Use SQLite to Manage Data in iOS Apps

Among the numerous applications existing on the App Store today, it would be hard for someone to find more than a few of them that do not deal with data. Most of the apps handle some sort of data, no matter in what format they are, and always perform some actions upon it. There are various solutions offered to developers for storing and managing data, and usually each one of them is suitable for different kind of applications. However, when working with large amount of data, the preferred method it seems like a one-way path: That is the use of a database.

Indeed, making use of a database can solve various kind of problems that should be solved programmatically in other cases. For programmers who love working with databases and SQL, this is the favorite data-managing method at 90% of the cases, and the first think that crosses their minds when talking about data. Also, if you were used to working with other databases or database management systems (DBMSs), then you’ll really appreciate the fact that you can keep applying your SQL knowledge in the iOS platform as well.

The database that can be used by apps in iOS (and also used by iOS) is called SQLite, and it’s a relational database. It is contained in a C-library that is embedded to the app that is about to use it. Note that it does not consist of a separate service or daemon running on the background and attached to the app. On the contrary, the app runs it as an integral part of it. Nowadays, SQLite lives its third version, so it’s also commonly referred as SQLite 3.

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