DEV Community: Anurag Roy

Swift: Passing data between view controllers

Anurag Roy — Thu, 18 Apr 2024 15:40:14 +0000

There are multiple options for passing data between view controllers.

Using Navigation Controller Push
Using Segue
Using Delegate
Using Notification Observer
Using Block

*Step 1. Declare variable in ViewControllerB
*

var isSomethingEnabled = false

*Step 2. Print Variable in ViewControllerB' ViewDidLoad method
*


override func viewDidLoad() {
    super.viewDidLoad()
    // Print value received through segue, navigation push
    print("Value of 'isSomethingEnabled' from ViewControllerA: ", isSomethingEnabled)
}

Step 3. In ViewControllerA Pass Data while pushing through Navigation Controller

if let viewControllerB = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "ViewControllerB") as? ViewControllerB {
    viewControllerB.isSomethingEnabled = true
    if let navigator = navigationController {
        navigator.pushViewController(viewControllerB, animated: true)
    }
}

So here is the complete code for:

ViewControllerA


import UIKit

class ViewControllerA: UIViewController  {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    // MARK: Passing data through navigation PushViewController
    @IBAction func goToViewControllerB(_ sender: Any) {

        if let viewControllerB = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "ViewControllerB") as? ViewControllerB {
            viewControllerB.isSomethingEnabled = true
            if let navigator = navigationController {
                navigator.pushViewController(viewControllerB, animated: true)
            }
        }
    }
}

*ViewControllerB
*


import UIKit

class ViewControllerB: UIViewController {

    // MARK:  - Variable for Passing Data through Navigation push
    var isSomethingEnabled = false

    override func viewDidLoad() {
        super.viewDidLoad()
        // Print value received through navigation push
        print("Value of 'isSomethingEnabled' from ViewControllerA: ", isSomethingEnabled)
    }
}

Passing Data through Segue: From ViewControllerA to ViewControllerB

Step 1. Create Segue from ViewControllerA to ViewControllerB and give Identifier = showDetailSegue in Storyboard as shown below

**
Step 2. In ViewControllerB Declare a viable named isSomethingEnabled and print its value.**
**
Step 3. In ViewControllerA pass isSomethingEnabled's value while passing Segue**

So here is the complete code for:

*ViewControllerA
*

import UIKit

class ViewControllerA: UIViewController  {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    // MARK:  - - Passing Data through Segue  - -
    @IBAction func goToViewControllerBUsingSegue(_ sender: Any) {
        performSegue(withIdentifier: "showDetailSegue", sender: nil)
    }

    // Segue Delegate Method
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if (segue.identifier == "showDetailSegue") {
            let controller = segue.destination as? ViewControllerB
            controller?.isSomethingEnabled = true//passing data
        }
    }
}

*ViewControllerB
*

import UIKit

class ViewControllerB: UIViewController {
    var isSomethingEnabled = false

    override func viewDidLoad() {
        super.viewDidLoad()
        // Print value received through segue
        print("Value of 'isSomethingEnabled' from ViewControllerA: ", isSomethingEnabled)
    }
}

Passing Data through Delegate: From ViewControllerB to ViewControllerA

Step 1. Declare Protocol ViewControllerBDelegate in the ViewControllerB file, but outside the class


protocol ViewControllerBDelegate: NSObjectProtocol {

    // Classes that adopt this protocol MUST define
    // this method -- and hopefully do something in
    // that definition.
    func addItemViewController(_ controller: ViewControllerB?, didFinishEnteringItem item: String?)
}

*Step 2. Declare Delegate variable instance in ViewControllerB
*

var delegate: ViewControllerBDelegate?

Step 3. Send data for delegate inside viewDidLoad method of ViewControllerB

delegate?.addItemViewController(self, didFinishEnteringItem: "Data for ViewControllerA")

*Step 4. Confirm ViewControllerBDelegate in ViewControllerA
*

class ViewControllerA: UIViewController, ViewControllerBDelegate  {
// to do
}

Step 5. Confirm that you will implement a delegate in ViewControllerA

if let viewControllerB = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "ViewControllerB") as? ViewControllerB {
    viewControllerB.delegate = self//confirming delegate
    if let navigator = navigationController {
        navigator.pushViewController(viewControllerB, animated: true)
    }
}

Step 6. Implement delegate method for receiving data in ViewControllerA


func addItemViewController(_ controller: ViewControllerB?, didFinishEnteringItem item: String?) {
    print("Value from ViewControllerB's Delegate", item!)
}

So here is the complete code for:

*ViewControllerA
*

import UIKit

class ViewControllerA: UIViewController, ViewControllerBDelegate  {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    // Delegate method
    func addItemViewController(_ controller: ViewControllerB?, didFinishEnteringItem item: String?) {
        print("Value from ViewControllerB's Delegate", item!)
    }

    @IBAction func goToViewControllerForDelegate(_ sender: Any) {

        if let viewControllerB = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "ViewControllerB") as? ViewControllerB {
            viewControllerB.delegate = self
            if let navigator = navigationController {
                navigator.pushViewController(viewControllerB, animated: true)
            }
        }
    }
}

*ViewControllerB
*

import UIKit
//Protocol decleare
protocol ViewControllerBDelegate: NSObjectProtocol {
    // Classes that adopt this protocol MUST define
    // this method -- and hopefully do something in
    // that definition.
    func addItemViewController(_ controller: ViewControllerB?, didFinishEnteringItem item: String?)
}

class ViewControllerB: UIViewController {
    var delegate: ViewControllerBDelegate?

    override func viewDidLoad() {
        super.viewDidLoad()
        // MARK:  - - - -  Set Data for Passing Data through Delegate  - - - - - -
        delegate?.addItemViewController(self, didFinishEnteringItem: "Data for ViewControllerA")
    }
}

Passing Data through Notification Observer: From ViewControllerB to ViewControllerA

Step 1. Set and post data in the notification observer in ViewControllerB

let objToBeSent = "Test Message from Notification"
NotificationCenter.default.post(name: Notification.Name("NotificationIdentifier"), object: objToBeSent)
*Step 2. Add Notification Observer in ViewControllerA
*
NotificationCenter.default.addObserver(self, selector: #selector(self.methodOfReceivedNotification(notification:)), name: Notification.Name("NotificationIdentifier"), object: nil)
*Step 3. Receive Notification data value in ViewControllerA
*

@objc func methodOfReceivedNotification(notification: Notification) {
    print("Value of notification: ", notification.object ?? "")
}

So here is the complete code for:

*ViewControllerA
*

import UIKit

class ViewControllerA: UIViewController{

    override func viewDidLoad() {
        super.viewDidLoad()

        // Add observer in controller(s) where you want to receive data
        NotificationCenter.default.addObserver(self, selector: #selector(self.methodOfReceivedNotification(notification:)), name: Notification.Name("NotificationIdentifier"), object: nil)
    }

    // MARK: Method for receiving Data through Post Notification
    @objc func methodOfReceivedNotification(notification: Notification) {
        print("Value of notification: ", notification.object ?? "")
    }
}

ViewControllerB

import UIKit

class ViewControllerB: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // MARK:Set data for Passing Data through Post Notification
        let objToBeSent = "Test Message from Notification"
        NotificationCenter.default.post(name: Notification.Name("NotificationIdentifier"), object: objToBeSent)
    }
}

_Passing Data through Block: From ViewControllerB to ViewControllerA
_
*Step 1. Declare block in ViewControllerB
*


var authorizationCompletionBlock:((Bool)->())? = {_ in}

*Step 2. Set data in block in ViewControllerB
*

if authorizationCompletionBlock != nil
{
    authorizationCompletionBlock!(true)
}

Step 3. Receive block data in ViewControllerA

// Receiver Block
controller!.authorizationCompletionBlock = { isGranted in
    print("Data received from Block is: ", isGranted)
}

So here is the complete code for:

ViewControllerA

import UIKit

class ViewControllerA: UIViewController  {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    // MARK:Method for receiving Data through Block
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if (segue.identifier == "showDetailSegue") {
            let controller = segue.destination as? ViewControllerB
            controller?.isSomethingEnabled = true

            // Receiver Block
            controller!.authorizationCompletionBlock = { isGranted in
                print("Data received from Block is: ", isGranted)
            }
        }
    }
}

ViewControllerB

import UIKit

class ViewControllerB: UIViewController {

    // MARK: Variable for Passing Data through Block
    var authorizationCompletionBlock:((Bool)->())? = {_ in}

    override func viewDidLoad() {
        super.viewDidLoad()

        // MARK: Set data for Passing Data through Block
        if authorizationCompletionBlock != nil
        {
            authorizationCompletionBlock!(true)
        }
    }
}

Swift: Passing data between view controllers

Anurag Roy — Thu, 18 Apr 2024 15:40:10 +0000

There are multiple options for passing data between view controllers.

Using Navigation Controller Push
Using Segue
Using Delegate
Using Notification Observer
Using Block

*Step 1. Declare variable in ViewControllerB
*

var isSomethingEnabled = false

*Step 2. Print Variable in ViewControllerB' ViewDidLoad method
*


override func viewDidLoad() {
    super.viewDidLoad()
    // Print value received through segue, navigation push
    print("Value of 'isSomethingEnabled' from ViewControllerA: ", isSomethingEnabled)
}

Step 3. In ViewControllerA Pass Data while pushing through Navigation Controller

if let viewControllerB = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "ViewControllerB") as? ViewControllerB {
    viewControllerB.isSomethingEnabled = true
    if let navigator = navigationController {
        navigator.pushViewController(viewControllerB, animated: true)
    }
}

So here is the complete code for:

ViewControllerA


import UIKit

class ViewControllerA: UIViewController  {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    // MARK: Passing data through navigation PushViewController
    @IBAction func goToViewControllerB(_ sender: Any) {

        if let viewControllerB = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "ViewControllerB") as? ViewControllerB {
            viewControllerB.isSomethingEnabled = true
            if let navigator = navigationController {
                navigator.pushViewController(viewControllerB, animated: true)
            }
        }
    }
}

*ViewControllerB
*


import UIKit

class ViewControllerB: UIViewController {

    // MARK:  - Variable for Passing Data through Navigation push
    var isSomethingEnabled = false

    override func viewDidLoad() {
        super.viewDidLoad()
        // Print value received through navigation push
        print("Value of 'isSomethingEnabled' from ViewControllerA: ", isSomethingEnabled)
    }
}

Passing Data through Segue: From ViewControllerA to ViewControllerB

Step 1. Create Segue from ViewControllerA to ViewControllerB and give Identifier = showDetailSegue in Storyboard as shown below

**
Step 2. In ViewControllerB Declare a viable named isSomethingEnabled and print its value.**
**
Step 3. In ViewControllerA pass isSomethingEnabled's value while passing Segue**

So here is the complete code for:

*ViewControllerA
*

import UIKit

class ViewControllerA: UIViewController  {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    // MARK:  - - Passing Data through Segue  - -
    @IBAction func goToViewControllerBUsingSegue(_ sender: Any) {
        performSegue(withIdentifier: "showDetailSegue", sender: nil)
    }

    // Segue Delegate Method
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if (segue.identifier == "showDetailSegue") {
            let controller = segue.destination as? ViewControllerB
            controller?.isSomethingEnabled = true//passing data
        }
    }
}

*ViewControllerB
*

import UIKit

class ViewControllerB: UIViewController {
    var isSomethingEnabled = false

    override func viewDidLoad() {
        super.viewDidLoad()
        // Print value received through segue
        print("Value of 'isSomethingEnabled' from ViewControllerA: ", isSomethingEnabled)
    }
}

Passing Data through Delegate: From ViewControllerB to ViewControllerA

Step 1. Declare Protocol ViewControllerBDelegate in the ViewControllerB file, but outside the class


protocol ViewControllerBDelegate: NSObjectProtocol {

    // Classes that adopt this protocol MUST define
    // this method -- and hopefully do something in
    // that definition.
    func addItemViewController(_ controller: ViewControllerB?, didFinishEnteringItem item: String?)
}

*Step 2. Declare Delegate variable instance in ViewControllerB
*

var delegate: ViewControllerBDelegate?

Step 3. Send data for delegate inside viewDidLoad method of ViewControllerB

delegate?.addItemViewController(self, didFinishEnteringItem: "Data for ViewControllerA")

*Step 4. Confirm ViewControllerBDelegate in ViewControllerA
*

class ViewControllerA: UIViewController, ViewControllerBDelegate  {
// to do
}

Step 5. Confirm that you will implement a delegate in ViewControllerA

if let viewControllerB = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "ViewControllerB") as? ViewControllerB {
    viewControllerB.delegate = self//confirming delegate
    if let navigator = navigationController {
        navigator.pushViewController(viewControllerB, animated: true)
    }
}

Step 6. Implement delegate method for receiving data in ViewControllerA


func addItemViewController(_ controller: ViewControllerB?, didFinishEnteringItem item: String?) {
    print("Value from ViewControllerB's Delegate", item!)
}

So here is the complete code for:

*ViewControllerA
*

import UIKit

class ViewControllerA: UIViewController, ViewControllerBDelegate  {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    // Delegate method
    func addItemViewController(_ controller: ViewControllerB?, didFinishEnteringItem item: String?) {
        print("Value from ViewControllerB's Delegate", item!)
    }

    @IBAction func goToViewControllerForDelegate(_ sender: Any) {

        if let viewControllerB = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "ViewControllerB") as? ViewControllerB {
            viewControllerB.delegate = self
            if let navigator = navigationController {
                navigator.pushViewController(viewControllerB, animated: true)
            }
        }
    }
}

*ViewControllerB
*

import UIKit
//Protocol decleare
protocol ViewControllerBDelegate: NSObjectProtocol {
    // Classes that adopt this protocol MUST define
    // this method -- and hopefully do something in
    // that definition.
    func addItemViewController(_ controller: ViewControllerB?, didFinishEnteringItem item: String?)
}

class ViewControllerB: UIViewController {
    var delegate: ViewControllerBDelegate?

    override func viewDidLoad() {
        super.viewDidLoad()
        // MARK:  - - - -  Set Data for Passing Data through Delegate  - - - - - -
        delegate?.addItemViewController(self, didFinishEnteringItem: "Data for ViewControllerA")
    }
}

Passing Data through Notification Observer: From ViewControllerB to ViewControllerA

Step 1. Set and post data in the notification observer in ViewControllerB

@objc func methodOfReceivedNotification(notification: Notification) {
    print("Value of notification: ", notification.object ?? "")
}

So here is the complete code for:

*ViewControllerA
*

import UIKit

class ViewControllerA: UIViewController{

    override func viewDidLoad() {
        super.viewDidLoad()

        // Add observer in controller(s) where you want to receive data
        NotificationCenter.default.addObserver(self, selector: #selector(self.methodOfReceivedNotification(notification:)), name: Notification.Name("NotificationIdentifier"), object: nil)
    }

    // MARK: Method for receiving Data through Post Notification
    @objc func methodOfReceivedNotification(notification: Notification) {
        print("Value of notification: ", notification.object ?? "")
    }
}

ViewControllerB

import UIKit

class ViewControllerB: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // MARK:Set data for Passing Data through Post Notification
        let objToBeSent = "Test Message from Notification"
        NotificationCenter.default.post(name: Notification.Name("NotificationIdentifier"), object: objToBeSent)
    }
}

_Passing Data through Block: From ViewControllerB to ViewControllerA
_
*Step 1. Declare block in ViewControllerB
*


var authorizationCompletionBlock:((Bool)->())? = {_ in}

*Step 2. Set data in block in ViewControllerB
*

if authorizationCompletionBlock != nil
{
    authorizationCompletionBlock!(true)
}

Step 3. Receive block data in ViewControllerA

// Receiver Block
controller!.authorizationCompletionBlock = { isGranted in
    print("Data received from Block is: ", isGranted)
}

So here is the complete code for:

ViewControllerA

import UIKit

class ViewControllerA: UIViewController  {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    // MARK:Method for receiving Data through Block
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if (segue.identifier == "showDetailSegue") {
            let controller = segue.destination as? ViewControllerB
            controller?.isSomethingEnabled = true

            // Receiver Block
            controller!.authorizationCompletionBlock = { isGranted in
                print("Data received from Block is: ", isGranted)
            }
        }
    }
}

ViewControllerB

import UIKit

class ViewControllerB: UIViewController {

    // MARK: Variable for Passing Data through Block
    var authorizationCompletionBlock:((Bool)->())? = {_ in}

    override func viewDidLoad() {
        super.viewDidLoad()

        // MARK: Set data for Passing Data through Block
        if authorizationCompletionBlock != nil
        {
            authorizationCompletionBlock!(true)
        }
    }
}

Error: Cannot find module '/path/.next/build-manifest.json'

Anurag Roy — Thu, 18 Apr 2024 15:29:42 +0000

there are several optional ways.

Adding:

"engines": {
    "node": ">=12.x"
  }

on your package.json may work

Adding:

sass as dev-dependency in your package.json,
Then, Run

yarn add -D sass

Then

Run yarn remove node-sass

Remove .next folder

DFS in one shot!

Anurag Roy — Thu, 18 Apr 2024 15:10:55 +0000

We use DFS in Tree and Graph.

You must know **recursion **before jumping into DFS

Recursion

Now to write a recursive function there are only 2 things-

`int recur(int n) {
if(n == 0) // known as base case

return n-1; // operation you want to perform!
`

Now see DFS as a recursive function-

What we do in Graph using DFS?
_ -> We just visit each node of the graph_

So in this case-

When should we stop? What is the base case?

-> When we encounter the same cell, visited earlier we should stop.

So, if (Vis[currnode] == True), means we have already visited the node, we should stop.

So code will be like this-

Void dfs(int currnode) { if(Vis[currnode] == true) return; }

step 1 is done--

now step 2 of recursion is to write what you want to perform-

we want to traverse the graph.
How we can do this?
-> By going from one cell to other-

So code will be like this-


for (auto it : adj[currnode]) {  // go to all it's neighbours
  if(!vis[it]) {              // check if it's been visited already
     cout << it << ' ';       // print it
     vis[it] = true; // make sure mark currentnode visited = true
     dfs(it);        // call the dfs again(recursion)
}

so final code will be like this-

Void dfs(int currnode) {

**// step 1**

if(Vis[currnode] == true) return;

**// step 2**

for (auto it : adj[currnode]) {  // go to all it's neighbours
  if(!vis[it]) {              // check if it's been visited already
     cout << it << ' ';       // print it
     vis[it] = true; // make sure mark currentnode visited = true
     dfs(it);        // call the dfs again(recursion)
}

}

Keep it in mind: Your output will be different, if you choose different node as your currentnode

Git revert vs Git reset

Anurag Roy — Fri, 02 Sep 2022 18:25:18 +0000

Both the git revert and git reset commands undo previous commits. But if you've already pushed your commit to a remote repository, it is recommended that you do not use git reset since it rewrites the history of commits. This can make working on a repository with other developers and maintaining a consistent history of commits very difficult.

Instead, it is better to use git revert, which undoes the changes made by a previous commit by creating an entirely new commit, all without altering the history of commits.

pip install dlib error

Anurag Roy — Fri, 26 Aug 2022 17:38:18 +0000

while we try to install dlib by the pip command pip install dlib, we may get the error: subprocess-exited-with-error

To get rid of the error, we have to run this command before that
pip install cmake , then we can run the command pip install dlib

Error: listen EADDRINUSE: address already in use XXXX

Anurag Roy — Sun, 05 Jun 2022 17:32:26 +0000

while running the npm script (npm start) you may encounter the command, this basically occurs when we have previously run the file in same port, to avoid this what we have to do is----

go to the server.js file then
update this
Server.HTTP_PORT = WXYZ;
Server.HTTPS_PORT = ABCD;
i.e. change WXYZ to something else and ABCD to something else

then again run npm start
then it will successfully get started in the updated port address.

run typescript file

Anurag Roy — Mon, 02 May 2022 14:27:47 +0000

You must have npm, nodejs install in ur os.
On cmd or other terminal run the command
npm install -g typescript
In any code editor write a typescript code and
save it with ** .ts ** extension.

// ignore * in commands

Now in terminal run these two commands one after another
command1_
```
** tsc file_name.ts **
```

//tsc (typescript compiler will compile it and convert it
// into js file

then run the following command
command2_

    ** node file_name.js **

:) you have successfully compiled and executed ur typescript file

time complexity difference between set & vector

Anurag Roy — Sun, 06 Mar 2022 07:46:53 +0000

for set: 4.720976s wall, 4.711230s user + 0.000000s system = 4.711230s CPU (99.8%) (also tested set::insert which takes little time)

for vector: 1.407571s wall, 1.404009s user + 0.000000s system = 1.404009s CPU (99.7%)

Blockchain- truffle migrate command error

Anurag Roy — Thu, 17 Feb 2022 05:50:46 +0000

sometimes we will face the problem while trying to run the command
$ truffle migrate
instead of this command if we will run the command
$ truffle migrate --reset

this way we can fix the error 100%

install all modules using only this pip command

Anurag Roy — Fri, 14 Jan 2022 12:04:20 +0000

pip freeze | %{$_.split('==')[0]} | %{pip install --upgrade $_}

vehicle counter

Anurag Roy — Wed, 08 Dec 2021 13:38:46 +0000

AI openCV vehicle counter project.