Working with Swift

Swift is Apple's new development language. When we switch from Objective C to Swift , we need some tricks so that we can reuse the code and can write less code  for our app .

1) Use Extension: 

Try to code less and reuse it whenever it's possible. Follow write once and use many  approach. For example, in our app there may be a requirement that most of the views should have border and round corner .
For this we can  write those line of code for each view in our view controller . But a better approach is that we can  write an extension to UIView, which will make the input view to have border and round corner.

extension UIView{

    

    func makeCornerRound(cornerRadius:CGFloat){

        self.layer.cornerRadius = cornerRadius

        self.layer.masksToBounds = true

    }

    

    func addBorderWith(color:UIColor, width:CGFloat){

        self.layer.borderWidth = width

        self.layer.borderColor = color.cgColor

        

    }

}

To use these as:

let myView = UIView()

myView.makeCornerRound(cornerRadius:3)

myView.addBorderWith(color:UIColor.gray,width:1.0)

2) Optional Unwrapping:

Guard vs If let

 var email:String?
var password:String?
if let mail_id = email{
  if let pwd = password {
    print("Welcome to my app!")
   }
}

The above code can be written with Guard statement like this:
guard let mail = email, let pwd = password  else{
   print("ohh no! we don't have email and password")
   return
}
print("Welcome to my app!")

You can see the difference here. The scope of unwrapped variable remains to the function in which they are unwrapped with Guard statement. But with if let , the scope is limits to the block in which they are unwrapped.

3) Nil Coalescing : 

What if the value of the optional is missing and you want to  perform some action in case of the absence of the value of an optional . Let's understand  this with an example:

var userName:String?

if let name = userName{
  print("Welcome \(user)")
} else{
  print("Welcome Guest")
}

We can short the above code with nil coalescing operator .

let name =  userName ?? "Guest"
print("Welcome \(name)")

Working with string and character in Swift

In swift string is value type. In Swift string type is built from Unicode scalar values. A unicode scalar is a unique 21 bit number for a character.

To write an arbitrary scalar value , use \u{n}, where n is a 1-8 digit hexadecimal number with a value equal to a valid Unicode code point.
For example:

let dollar = "\u{24}"

let baby:Character = "\u{1f425}"

Using Extended grapheme cluster we can create a single character by many complex script characters.

An Extended grapheme cluster is a sequence of one or more unicode scalar  that produce a  single human readable character.

let eInCircle:Character = "\u{E9}\u{20DD}"

Will print "é⃝"

String indices: 

In swift different characters require different amount of memory  to store , so in order to determine the position of a character, we must iterate over each unicode scalar from start or end of that string .That's why string in swift can not be indexed by integer values.

A) To get the position of the first character , use the startIndex property of the string:

  var name = "Budha"

   
  To get the first character of the name,

   let firstChar =  name[name.startIndex]

B) The endIndex property  is position after the last character in the string. So to access the last character in the string, use:

let endIndex = name.endIndex

let lastChar = name[name.index(before: endIndex)]

C) To check the equality for string and character, we use ==(equal to ) and != (not equal  to )operator. Two string value will be considered equal if their Extended grapheme clusters are canonically equal. Extended grapheme clusters are canonically equal if they have the same linguistic meaning and appearance, even if they are composed from  different Unicode scalars behind the scenes.

Reference: https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/StringsAndCharacters.html

Operation on Collection in Swift

In iOS app development we need to perform some task on collection (Array,dictionary..) in swift. For example to get the sum of the element in an array we could go for for-in loop . Do code like this:

let arr =  [1,3, 4,6,9]

var sum = 0
for i in arr{
sum += i
}

We can achieve such kind of task very easily with a line of code.

Working with Map, filter, reduce and flatMap:

To get the sum of all element we can write

let sum =  arr.reduce(0,+)

Map:

We use map to  loop over the collection and apply a same  on each element in collection. For example to get the square of of each element in an array we could go for for in loop and to square of each element in an array.

With map, we can do this task this way:
let arr = [1,2,4,5,6,7,8,9]

let squares =  arr.map{$0 * $0}

The map function has a single argument which is a closure. Map function calls this closure as it loop over the collection. This closure takes an element from the collection as an argument and returns result. The map function return the result in an array.

We can  write above line of code as:

let squares2 =  arr.map{element in   element * element}

The keyword  in separates  the argument from the body of the closure .

The map operation can be performed on each collection type it is not limited to just an array. We can use this with dictionary, set also. But the result of the operation is always an array.

Filter: We use filter where we want to filter the collection  of data with a condition. Filter function loop over the collection  and returns only those element from the collection which satisfy  a given condition in include.

let arrData  = [1,23,45,,4,6,8,3]

For example : To get only those element from above array which is even, we write:

let arrEven = arrData.filter{ $0 %2 == 0}

Reduce: reduce method used to combine all elements in a collection to create a single value . The reduce() method takes two arguments, an initial value and a closure

let  fullStatement  = arr.reduce("==") {text, name in "\(text),\(name)"}

FlatMap: Used to flatten to  collection of   collections.

let complexArray  = [[2,3,5],[34,56], [34,56,78]]

let flat =  complexArray.flatMap {$0 }

The above line of code will combine all sub array  from complexArray into  a single array.

With flatMap and  chaining of the above methods we can solve complex queries on collection .

For example: get all even elements from complexArray

let   evenNums  = complexArray.flatMap{ 
                  subArray in subArray.filter{ $0 %2 == 0}
             }

In short form we can write above line as:
let evenInShortForm =  complexArray.flatMap { $0.filter{ $0 %2 == 0  }}

References:http://useyourloaf.com

Sort Array in swift

To sort an array we can use sort() which all arrays have in default. We can use sort() and sorted() to sort an array.

To sort an simple array like this, we can use sort() as:

var arr =  [ "orange","Apple" "Grapes","banana"]

arr.sort()


To sort an array of custom object like custom struct or class we  use sort() using a trailing closure that sort an array on field we specify.

For example: We have an array of custom object Opportunity which have a string field date . So to sort this array on date field, here we will first convert string date to Date object . Let's have a look on below code:To sort arrOpportunities on a string field say title,

arrOpportunities.sort{

$0.title.compare($1.title) == NSComparisonResult.OrderedAscending
}

 If we have title say:
["hello","ok","arm","Basket"]  then using  above code will results in

["Basket","arm","hello","ok"]

To get results in ignoring the case we can use localizedCompare() like this:

arrOpportunities.sort{

$0.title.localizedCompare($1.title) == NSComparisonResult.OrderedAscending
}

will result in
["arm","Basket","hello","ok"]

If we want to return an array after doing sort we can use sorted() like this

var arr_sorted =  arrOpportunities.sorted{

$0.title.localizedCompare($1.title) == NSComparisonResult.OrderedAscending
}

Integrate third party library in an iOS project:

In iOS app development we need many other libraries to be included in our app to accomplish set of task. There are number of ways by which we can include these library  in our project .

1) Using Cocoapods 

Cocoa pod is dependency manager . It is very simple to add library this way . Go to project directory and follow these steps:

a) Run pod init  command

    The above command will initialize the pod in project directory and creates a pod file. 

b) Now open the pod file and add  required library in this file . And save the file .

c) Run pod install command .

    This will install the library in project directory  and creates a xcworkspace  file in project directory .

     From now open the xcworkspace instead of Xcode project . 

2) Manually:

Using this way , we just drag and drop the required files/folder of required library to our project.

3) using git sub module:

Using this way we add a third party project using git command . This command will add third party library as a submodule in our project.

a) Go to your project directory , initialize git if git is not initialized in project directory .

      

     git init 

   

 b) git submodule add  project-url

    The above command will add third party library at given url as a sub module in our project .

Manage navigation controller

In iOS app development UINavigationController play a vital role . As we all know UINavigationController keeps the stack of view controller when we use in our app for transition among view controllers .

We face many problems related to UINavigationController like change appearance of the navigation bar, add UIBarButton items to navigation bar , combine the status bar with navigation bar and some others. All these tasks seem very easy at first look but it depends on our requirements .

In my recent app I want to use the navigation bar with two buttons (left and right bar button item)in all view controller and also want the color of status bar and navigation bar should be same . 

1) To change the appearance of the UINaviagtionBar, we can code in our AppDelegate this will reflect in all view controllers: 

    var navBarAppearance = UINavigationBar.appearance()

    navBarAppearance.tintColor = UIColor.white

    navBarAppearance.barTintColor  = UIColor.init(red: 73/255.0, green: 180/255.0, blue: 255/255.0, alpha: 1)

 a) Here tintColor attribute will change the background color of the navigation bar .

 b) Bar tint color will change the color of button titles and  button images.

The above two properties won't change the color of the title of the navigation bar. To change the color of the title use this line of code:

   

   navBarAppearance.titleTextAttributes = [NSForegroundColorAttributeName:UIColor.white]

 2) Change the status bar color:

  UIApplication.shared.statusBarStyle = .lightContent

This will not change the color of the status bar. To reflect the change we need to make one more change in our info.plist file:

set UIViewControllerBasedAppearance to false

3) Add bar button items to all view controller: This was my requirement to have two buttons in navigation bar in all view controllers: I can not achieve this like appearance. Because bar buttons are added to navigation item property of the view controller. Each view controller have its own navigation item . 

So to add bar  buttons to all view controller:

a) Add in viewDidLoad() of each view controller

b) Make a Utility class and add a class function to it and call this from each view controller's viewDidLoad() or any other methods of view life cycle as per your need .

c) Make an separate subclass of UIViewController and add two bar buttons here in this class and change the super class of your view controller from UIViewController to one you created previous .

I will  choose the last approach. Add this code in your subclass:

     let leftBtn = UIBarButtonItem(image: UIImage(named:"back_btn_icon"), style: .plain, target: self, action: #selector(backBtnTapped))

   self.navigationItem.leftBarButtonItem = leftBtn

    let rightBtn = UIBarButtonItem(image: UIImage(named:"setting_icon"), style: .plain, target: self, action: #selector(settingBtnTapped))

    self.navigationItem.rightBarButtonItem = rightBtn

What if one of your view controller need only one bar button. It's easy we can hide the unwanted button:

 To hide the left button add this line your view controller:

self.navigationItem.leftBarButtonItems?.remove(at: 0)

Reference: Stackoverflow and https://coderwall.com

Set attributed text in interface builder

 1) Increase font size as size of UILabel increases:

There may be a requirement to increase the font size as the size of UILabel increases.To see this in action, Open Xcode and switch to xib/storyboard file and follow these steps:

Take a UILabel and  set height of the UILabel to the proportional to the height of screen . and set other required constraint on UILabel.
Then set some properties of UILabel to have font size proportional to the size of UILabel.

a) Set AutoShrink to minimum font size
b) set number of lines to 0
c) set the font size bigger as the maximum size of UILabel .

2) Set Attributed text in interface builder for a UILabel:

We can set attributed text programatically by setting different attributes like font, color, size on a attributed string(instance of NSAttributedString) . But there is an easy way , we can create an attributed text without typing even a single line of code.

We can create an attributed text in interface builder. To set attributed text for a UILabel :

a) Change text type  plain to attributed  in the attributes inspector window.
b) Then type the string as your requirements.
c) Then select  word you want to change the appearance  of and change it's size, font family, color etc.