Forem: NalineeR

Struct vs Class

NalineeR — Tue, 25 Apr 2023 08:49:41 +0000

struct and class are the pillars of any Object Oriented Language. Main part is deciding when to use which one. To get the answer of this question we need know how they differ in properties. Let’s check one by one -

1. Reference vs Copy - Classes work on reference type whereas Structs work on Copy type. Suppose you create an instance A and later you create another instance B by assigning A to it. Now check their effects based on their types -
1. Class -> Change in A or B will show change in other one also because they are pointing to same address.
2. Struct -> change in A or B will not affect other because both the instances are separate. B is like a independent copy of A.

2. Inheritance - Classes allow us to inherit other classes whereas Structs don’t support inheritance.

Class inheritance - Below code snippet shows how class B has inherited class A.

class classA{
    var name = ""
}
class classB:classA{
    let type = ""

    func updateName(){
        //accessing property of inherited class A
      name = "updated name"
    }
}

Struct inheritance - Structs don't support inheritance hence complier will give error if we go for it.

3. init - Structs come with a default init function including all the properties which is known as property-wise initialisation. Whereas in Class you need to write your own init function.

class classA:NSObject{
    var name:String

    init(userName:String){
        name = userName
    }
}

struct structA{
    var name:String
    var skills:String
}

func demoOfInit(){
    let classObj = classA(userName: "class")
    let structObj = structA(name: "struct", skills: "default init")
}

4. deinit function - Class provides us the deinit function whereas in struct there is no such function.

class classA:NSObject{
    var name:String

    init(userName:String){
        name = userName
    }

    deinit{

    }
}

Now based on above differences you can easily decide our preference for specific case.

One example can be Modals -> In modals we go for Structs because we generally don't need their references or inheritance as they are usually used as independent objects.

inout parameters in Swift

NalineeR — Wed, 19 Apr 2023 07:56:49 +0000

Inout parameters are the parameters which hold the reference to the original variable. Hence, any change in those params directly affects the original variable.

*How to accept inout param - * We need to add an additional keyword 'inout' just before the data type of parameter as below.

Below example is a function that swaps the values of the original variables.

func swapValues(x:inout Int,y:inout Int){
   let z = x
   x = y
   y = z
}

*How to pass inout values - * While passing variable to inout type , we need to add the ampersand (&) with variable name. Check below -

override func viewDidLoad() {
   super.viewDidLoad()
   // Do any additional setup after loading the view.
   print("BeforeSwap-> a->\(a), b->\(b)")
   swapValues(x: &a, y: &b)
   print("AfterSwap-> a->\(a), b->\(b)")
}

When you run this code you will see below output -

Optional function in swift Protocol

NalineeR — Thu, 13 Apr 2023 09:51:48 +0000

In this article we will check how to make the protocol functions optional for implementation.

Let's create a protocol named Eatable and make our VegetableVC class conform to this.

protocol Eatable{
    func addItem()
}

class VegetableVC:Eatable{

}

You will get an error if you run with this code. Because the functions in protocol are of Required type by default i.e. whoever conforms to this will have to implement this.

So let's add the functions to remove this error.

class VegetableVC:Eatable{
    func add() {

    }
}

But what if we want to add a function which is optional to implement? Let's check how to do it -

First lets add a new function as follow - func delete()

Now we have 2 approaches to achieve the optional implementation -

1. using extension - In this we extend the protocol and provide a default implementation.

extension Eatable{
    func delete(){

    }
}

If you run the code now you see you don't get error even though VegetableVC class has not implemented the delete() method.

2. using optional keyword - In this approach we mark the function as optional using the keyword.

@objc protocol Eatable{
    func add()
    @objc optional func delete()
}

You can see we have marked protocol and func with @objc becuase 'optional' can only be applied to members of an @objc protocol.

Delete the extension we added previously and run the program.
It runs without any error.

Dependency Injection in swift

NalineeR — Mon, 10 Apr 2023 08:22:27 +0000

The approach used to provide the initial value to the property.
The purpose of this approach is to obtain the loosely coupled code.

There are three type to obtain this -

By Initialisation -> In this type we need to pass the initialisation value in the init func of the class

class DemoVC:UIViewController{
    override func viewDidLoad() {
        super.viewDidLoad()
        //passing dependency value by init func
        let obj = Language(langName: "Swift")
        print(obj.name)
    }
}

class Language{
    var name:String
    ///1. Initialisation Dependency Injection
    init(langName:String) {
        self.name = langName
    }
}

By Function -> In this type we pass the initial value as the function param. And the class property is initialised from this param.

class DemoVC:UIViewController{
    override func viewDidLoad() {
        super.viewDidLoad()
        //setting dependency value passing parameter in method
        let obj = Language()
        obj.getLanuageDetails(lanugage: "Swift")
    }
}

class Language{
    private var name:String!
    func getLanuageDetails(lanugage:String){
        name = lanugage
        print("Your have shown interest in \(lanugage) Language.")
    }
}

By Property -> Here we generally create / access the class property and set the value directly.

class DemoVC:UIViewController{
    override func viewDidLoad() {
        super.viewDidLoad()
        //setting dependency value by setting property directly
        let obj = Language()
        obj.name = "Objective C"
    }
}

class Language{
    var name:String = "Swift"
}

Variadic Function in Swift

NalineeR — Mon, 10 Apr 2023 05:30:17 +0000

The functions which takes Variadic parameter are called Variadic Functions.

Variadic parameters allow us to pass either single or multiple values based on our requirement.

Declaration - You just need to add Three Dots i.e. ... after param data type to make it variadic.

Example - Below function takes an Int as variadic param -

func getSum(values:Int...){
    let sum = values.reduce(0, +)
    print("Sum is-\(sum)")
}

Now let's check how can we call it -
case 1 - Call it with single value -

getSum(values: 8)

case 2 - Call it with multiple values -

getSum(values: 1,7)

escaping and non-escaping closure in Swift

NalineeR — Tue, 28 Mar 2023 06:58:54 +0000

In swift closures are of two types - escaping and non-escaping.

1.non-escaping - This is the default type of closure. This indicates that in function the control will not be back once gone.

func sumOfInt(a:Int,b:Int,handler:((Int)->())){
        let c = a + b
        handler(c)
 }

Above function takes two integer parameters and returns the sum in the handler.
Here the control will be gone after executing the line handler(c) and won't be back.

2.@escaping - In this type of closure control returns to function even after code block has been executed. For example the url session tasks. In this type the local properties are accessible even when the control is back hence to capture them we need to mark the closure as @escaping to notify swift.

func sumWithDelay(a:Int,b:Int,handler:@escaping((Int)->())){
        let c = a + b
        DispatchQueue.main.asyncAfter(deadline: .now()+1) {
            handler(c)
            //control comes back in given duration
        }
        //control will be gone
}

Handle varying DataType in Codable

NalineeR — Wed, 22 Mar 2023 13:17:41 +0000

Codable is a type alias for the Encodable and Decodable protocols. These protocols are used for encoding and decoding.

While decoding we often face a situation where the data type may change in response coming from Backend. Let's see how we can handle the case -

Scenario - We will be loading Employee data from a json file.

Step 1 - Let’s take a UILable for showing employees’ name and create an IBOutlet for it.

Step 2 - I have added an Employees’ json for demo purpose

Step 3 - Let’s create a file for Modal and create a codable struct for our Employees data

Step 4 - Our function loadDataFromJson(handler:@escaping((Data)->())) reads the json from Bundle and convert it’s content to Data. In the end it calls the handler with that data.

Step 5 - Now we parse the data into the Employees modal in the function func parseDataToEmployee(). After parsing to modal, we set Employees’ name and id on our label lblEmployee.

Below is how the ViewController file looks in the end.

Now run the project. Here comes the main part.
You get and error which says - "Expected to decode Int but found a string/data instead.", underlyingError: nil))”

This is coming because our Employee modal is expecting the id to be an Int but in JSON it is getting String somewhere.
You can check in the Employee.json that first object has id as String whereas all the other objects have it as Int.

Let’s check how to handle this case where the data type may vary.

The Codable protocol provides us an init function. We need to use this to handle our error. So let’s go to our Modal file and add the init function as follow -

init(from decoder: Decoder) throws {

        let container = try decoder.container(keyedBy: CodingKeys.self)

        if let intId = try? container.decode(Int.self, forKey: .id){
            //if received as int then parse as is
            id = intId
        }else if let strId = try? container.decode(String.self, forKey: .id){
            //if received as String then convert to Int and set
            id = Int(strId) ?? 0
        }else{
            id = 0
        }
        employeeName = try container.decode(String.self, forKey: .employeeName) 
    }

In the above init function we are using if else condition based on the received data type.
Now run the project one more and see the employee data is parsed with no error.
This is how it looks -

Project Link - https://github.com/NalineeR/CodableInitDemo.git

Swift Access Modifiers

NalineeR — Wed, 22 Mar 2023 08:07:05 +0000

Access modifiers are the identifiers which let us control the access level of class/struct/variable or methods.

In swift there are following Access Modifiers -
1. internal - This is the default one. When don't mention any then this is the default type of access the class/struct etc get.
In this one entities can be access and inherited within the target.

Access level - accessible & inheritable within target

2. private - With this one entities are only accessible within class scope and, when accessed out of class then will give error.

Access level - within enclosing declaration

Example - In below screenshot , the property osName is inaccessible due to private access.

3. fileprivate - Just as the name explains, the entities are accessible within enclosing declaration and within same file i.e in which it is declared.

Access level - within enclosing declaration & within same file

Example 1 - In below screenshot, the property osName is accessible out of its class scope because those classes are created in same file.

Example 2 - In below screenshot, the property osName is inaccessible because the class accessing it is not in the same file in which osName was created. Hence, causes error.

4. public - This makes the entity accessible among other targets also however, they can't be inherited in the other targets.

Access level - accessible in other targets but not inheritable out of self target

_Example 1 - _
Target 1 -> class ViewController
Target 2 > class NRDropDownHelper

NRDropDownHelper is inaccessible in Target 1 (ViewController class) due to it's default internal level. Hence, causes error.

_Example 2 - _

After changing the class access to public

It becomes accessible in ViewController
Yet can't be inherited outside target hence causes error.

5. open - This is the highest level of access in swift. With this entities are accessible and inheritable in outside target as well.

Access level - accessible and inheritable in other targets as well

example class NRDropDownHelper is access and is also inherited in class customHelper.

Common errors in releasing custom pod

NalineeR — Sat, 18 Mar 2023 13:57:04 +0000

There are a few common errors that we generally face while creating the Custom Pod.

Lets find out the reason of their occurrence and resolution -

1. Error 1 - Unable to accept duplicate entry for Pod (VersionNumber)

This error means that Pod with mentioned version number was already released and you are trying to release again on same version.

Note:- The version should be higher every time release your Pod.

So to resolve this follow the steps -

podspec file -> Increase the version number
commit and push to git
give the tag on commit (same tag as used in point 1)
now try pod trunk push

2. Error 2 - no file exists at source_files

This error means that your library files were not found at the path specified on podspec -> `s.source_files`.

This usually comes up because in the project created by Cocoapod the example file “Replace Me” comes up under classes folder.
But when you add / create your files on the same level as of Replace Me then it doesn’t get added to the classes folder.
But the path podspec -> s.source_files is still pointing to classes folder where it finds nothing and causes the error.

*How to resolve this ? *

Create a folder named Sources and add your files under this. NOTE: You can give any name to the folder. It doesn’t has to be just 'Sources'.
Update folder path under podspec as follow - s.source_files = 'Sources/**/*'

Happy Coding 🎉

Create You Own Pod

NalineeR — Mon, 13 Mar 2023 10:00:50 +0000

So far you would have used pods as a dependency in your project.
Do you want to create your own pod and help others?

Let's do it by below easy steps -

Open terminal and type the command -> pod lib create Your_Pod_Name
It will ask you some questions and then will create an XCode project for you. This Xcode project will contain some files added for you
1. .podspec -> will contain the details/specifications about your library
2. README.md -> the README file in markdown format.
3. License -> this will hold the default MIT license. You can replace with your own if required.
4. ReplaceMe.swift -> A default swift file to guide where to add your files.

Lets setup the project now -

README.md - Open this file and add/edit the details relevant to you. You can remove the details which are not required.
Addling classes -
1. Delete the Replace Me file.
2. Click on MyFirstPod under Pods and Create a folder with name Sources
3. Now add your library files to this folder.
Adding Resources - You need to add the resources like xib,asset,icons etc to a separate folder. If you don’t have any then you can skip this step.
1. Create a folder named Resources on the same level as we did for Sources.
2. Now add your resource files to it here
Update folder path in podspec file - Open you podspec file and set the following keys one by one
1. set s.source_files to this s.source_files = 'Sources/**/*.swift'
2. s.resources to below. You can add the extension of files you have added to your project. s.resources = "Resources/**/*.{png,xib}"
3. Add the description and summary for your project
Deploy your library -
1. Push to your Git Repo -
  1. Create a repository for this project and push your project to it.
  2. Now we need to add a tag to the last commit. This tag should be the one mentioned in podspec file on s.version. This tag is becomes the version of your pod.
2. Validate -
  1. Open terminal
  2. Traverse to the folder where the podspec file exists.
  3. Run pod lib lint --allow-warnings. This will validate your library.

3. Deploy to public - Run pod trunk push --allow-warnings. If everything goes right then you will see as below -

That's it. Now you can install this pod in any other project.🎉

You can find the demo project on below link -
https://github.com/NalineeR/NRCustomPod