Error Handling In Swift

Jitendra Kumar

26 February 2021

Error handling in swift is a process of recovering from error conditions in your project.

Swift provides the support to handle the error in your project.

In Swift, we using Error protocol to handle and define the error.

We can create the custom error type using the enum which needs to confirm the Error protocol.

Error handling in swift provides the help to change the program flow in run time when the error occurred.

We will use the swift try-catch block to handle the error in run time.

Swift Try Catch

When you calling any function and if the function has throws keyword. then that mean we need to use the try-catch block to handle the error.

do-> This is the block where we write the code which can throw the error.

try-> try use the front of the function which can throw the error when you call.

catch-> Catch block use when error throw by function then this block responsible for handle the error.

throws-> Throws keyword use when your function will return the error.

throw-> keyword is used for throwing errors from the error type defined.

Error handling example-> Employee age should be greater than 21

-> First we will create the own error type using an enum with Error protocol.

-> Then we will crate one controller for create the function which throw the error.

-> Then we will call the function in viewdidLoad function.

-> We are calling four times same functions with diffrent input. which provide us the error and success resposne according to condition.

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        //MARK:- when age negative
        do {
            try CheckEmployeeValidation(age: -20)
        } catch let error {
            print("Error:- \(error)")
        }
        //MARK:- when age zero
        do {
            try CheckEmployeeValidation(age: 0)
        } catch let error {
            print("Error:- \(error)")
        }
        //MARK:- when age less than twenty
        do {
            try CheckEmployeeValidation(age: 19)
        } catch let error {
            print("Error:- \(error)")
        }
        //MARK:- when age greater than twenty
        do {
            try CheckEmployeeValidation(age: 21)
        } catch let error {
            print("Error:- \(error)")
        }
    }
    
    func CheckEmployeeValidation(age: Int = 0) throws  {
        if age < 0 {
            throw EmployeeAgeError.ageShouldNotBeNegative
        } else if age == 0 {
            throw EmployeeAgeError.ageShouldNotBeZero
        } else if age < 20 {
            throw EmployeeAgeError.ageShouldBeGreaterThanTwenty
        } else {
            print("success:- \(age)")
        }
    }

}

enum EmployeeAgeError: Error {
    case ageShouldNotBeNegative
    case ageShouldNotBeZero
    case ageShouldBeGreaterThanTwenty
}

------------------Output------------------------

Error:- ageShouldNotBeNegative
Error:- ageShouldNotBeZero
Error:- ageShouldBeGreaterThanTwenty
success:- 21

import UIKit

class ViewController: UIViewController {

override func viewDidLoad() {

super.viewDidLoad()

//MARK:- when age negative

do {

try CheckEmployeeValidation(age: -20)

} catch let error {

print("Error:- \(error)")

}

//MARK:- when age zero

do {

try CheckEmployeeValidation(age: 0)

} catch let error {

print("Error:- \(error)")

}

//MARK:- when age less than twenty

do {

try CheckEmployeeValidation(age: 19)

} catch let error {

print("Error:- \(error)")

}

//MARK:- when age greater than twenty

do {

try CheckEmployeeValidation(age: 21)

} catch let error {

print("Error:- \(error)")

}

func CheckEmployeeValidation(age: Int = 0) throws {

if age < 0 {

throw EmployeeAgeError.ageShouldNotBeNegative

} else if age == 0 {

throw EmployeeAgeError.ageShouldNotBeZero

} else if age < 20 {

throw EmployeeAgeError.ageShouldBeGreaterThanTwenty

} else {

print("success:- \(age)")

}

enum EmployeeAgeError: Error {

case ageShouldNotBeNegative

case ageShouldNotBeZero

case ageShouldBeGreaterThanTwenty

}

------------------Output------------------------

Error:- ageShouldNotBeNegative

Error:- ageShouldNotBeZero

Error:- ageShouldBeGreaterThanTwenty

success:- 21

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