What is UIResponder Chain?

Ans : 

Apps receive and handle events using responder objects. A responder object is any instance of the UIResponder class, and common subclasses include UIView, UIViewController, and UIApplication. UIKit manages most responder-related behavior automatically, including how events are delivered from one responder to the next.

Example : 

For every event, UIKit designates a first responder and sends the event to that object first. The first responder varies based on the type of event. 

UIKit uses view-based hit testing to determine where touch events occur. Specifically, UIKit compares the touch location to the bounds of view objects in the view hierarchy. The hitTest:withEvent: method of UIViewwalks the view hierarchy, looking for the deepest subview that contains the specified touch. That view becomes the first responder for the touch event. 

If a touch location is outside of a view’s bounds, the hitTest:withEvent: method ignores that view and all of its subviews. As a result, when a view’s clipsToBounds property is NO, subviews outside of that view’s bounds are not returned even if they happen to contain the touch.

UIResponder Chain

• If the view is the root view of a view controller, the next responder is the view controller. 
• If the view is not the root view of a view controller, the next responder is the view’s superview. 
• If the view controller’s view is the root view of a window, the next responder is the window object. 
• If the view controller was presented by another view controller, the next responder is the presenting view controller. 
• UIWindow. The window’s next responder is the application object. 
• UIApplication. The app object’s next responder is the app delegate, but only if the app delegate is an instance of UIResponder and is not a view, view controller, or the app object itself.

What is lazy loading?

Ans :  Lazy Loading Images is a technique to resolve loading image from the web. The thing is that, I need to display images directly from the web in UIImageView or any other control. 

For this, if you simply try to set the image using in-built setImage method then your application gets stuck while loading image from the web. To overcome this issue, there is a technique generally known as Lazy Loading Image. The thing actually happening in lazy loading is that the task of image loading from web is performed in background and at that time a temporary placeholder image is displayed in the control. When the actual image is fully loaded from the web, it is replaced with the placeholder image and you get your actual image on the control without having stuck interface.

You can use third party library to load image :  SDWebImage

Try to make own coding for loading image from URL and Save in cache and display in imageView.

Which method called when I click on next, done button of keyboard?

Ans : textFieldShouldReturn

func textFieldShouldReturn(_ textField: UITextField) -> Bool {

     return false

}

What are UITextField delegate methods?

Ans : 

Copy from Apple Developer Site : Link

Managing Editing

func textFieldShouldBeginEditing(UITextField) -> Bool

Asks the delegate if editing should begin in the specified text field.

func textFieldDidBeginEditing(UITextField)

Tells the delegate that editing began in the specified text field.

func textFieldShouldEndEditing(UITextField) -> Bool

Asks the delegate if editing should stop in the specified text field. 

func textFieldDidEndEditing(UITextField, reason: UITextField.DidEndEditingReason)

Tells the delegate that editing stopped for the specified text field.

func textFieldDidEndEditing(UITextField)

Tells the delegate that editing stopped for the specified text field.

enum UITextField.DidEndEditingReason

Constants indicating the reason why editing ended in a text field.

Editing the Text Field’s Text

func textField(UITextField, shouldChangeCharactersIn: NSRange, replacementString: String) -> Bool

Asks the delegate if the specified text should be changed. 

func textFieldShouldClear(UITextField) -> Bool

Asks the delegate if the text field’s current contents should be removed.

func textFieldShouldReturn(UITextField) -> Bool

Asks the delegate if the text field should process the pressing of the return button.

Instance Methods

func textFieldDidChangeSelection(UITextField)

I have 100 cells. In each cell I have 5 button. How can I check which cell button is clicked?

Ans : 

There are various approach for this problem. But following two approach are better.

Approach-1 : Delegate - Protocol 

Cell : 

protocol CellSubclassDelegate: class {

    func buttonTapped(cell: CellSubclass)

}

class CellSubclass: UITableViewCell {

@IBOutlet var someButton: UIButton!

weak var delegate: CellSubclassDelegate?

override func prepareForReuse() {

    super.prepareForReuse()

    self.delegate = nil

}

@IBAction func someButtonTapped(sender: UIButton) {

    self.delegate?.buttonTapped(self)

}

ViewController:

class MyViewController: UIViewController, CellSubclassDelegate {

    @IBOutlet var tableview: UITableView!

    func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

        let cell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath) as! CellSubclass

        cell.delegate = self

    }

    func buttonTapped(cell: CellSubclass) {

        guard let indexPath = self.tableView.indexPathForCell(cell) else {

            // Note, this shouldn't happen - how did the user tap on a button that wasn't on screen?

            return

        }

        //  Do whatever you need to do with the indexPath

        print("Button tapped on row \(indexPath.row)")

    }

} 

Approach-2 Using Closure:

Cell :

class MyCell: UITableViewCell {

    var button: UIButton!

    var buttonAction: ((Any) -> Void)?

    @objc func buttonPressed(sender: Any) {

        self.buttonAction?(sender)

    }

}

ViewController : 

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

    let cell = tableView.dequeueReusableCellWithIdentifier("Cell") as! MyCell

    cell.buttonAction = { sender in

        // Do whatever you want from your button here.

    }

    // OR

    cell.buttonAction = buttonPressed(closure: buttonAction, indexPath: indexPath) // <- Method on the view controller to handle button presses.

}

No need to explain code. Simple as that.

If you have any comment, question, or recommendation, feel free to post them in the comment section below!

If there are two views up and bottom, up-view is 60% of superview and 40% of superview respectively, then what to do with constraint?

Ans : 

Use of multiplier in constraint

We took 2 views - Orange and Green. 

We set orange view's top, leading, trailing constraint to main view as 0. 

Same, we set green view's bottom, leading, trailing constraint to main views as 0.

Now,

We select height constraint of orange view equal to main view's height. And set multiplier 0.6. It shows ratio of orange view's height to main view's height. We have set 0.6 = 60/100 . So orange view's height become 60% of main view's height.

Set multiplier of height constraint in size inspector

Same we have done with green view and set multiplier 0.4 = 40/100 means 40%.

If you have any comment, question, or recommendation, feel free to post them in the comment section below!

How to call segue programmatic?

Ans : 

For segue first, We have to set identifier in Class Inspector right side in XCode. Through that identifier, we can call like

performSegue(withIdentifier: "identifier", sender: nil) 

What is Content Hugging and Content Compression Resistance Priority?

Ans : 

The priority really come in to play only if two different constraints conflict. The system will give importance to the one with higher priority. So, Priority is the tie-breaker in the autolayout world.

1. Content Hugging Priority : 

Larger the content hugging priority , the views bound will hug to the intrinsic content more tightly preventing the view to grow beyond its intrinsic content size. Setting a larger value to this priority indicates that we don’t want the view to grow larger than its content.

In above example, we set both label leading, trailing, top and bottom but not set width constraint. So here conflicts will occur. You can see red line between two label showing conflict.

Solution : If we have label's content hugging priority higher than there will be no conflicts as hight priority label will not grow its size more than its content size. See below image :

Blue label has more content hugging priority (251) than green label(250). Blue label's width will be set fixed as its content size.

2. Content Compression Resistance : 

Setting a higher value means that we don’t want the view to shrink smaller than the intrinsic content size. It's simple : Higher the priority means larger the resistance to get shrunk.

Example . One button having large name and auto layout is set on button as its width is become 40. So, button's content is not readable. See image :

Button horizontal compression resistance is 750 and width constraint priority is 1000.

For Solution, let's change horizontal compression resistance to 1000 and width constraint priority less than 1000 i.e 999 . Now see effect on below image :

Button horizontal compression resistance is 1000 and width constraint priority is 999.

If you have any comment, question, or recommendation, feel free to post them in the comment section below!

How To declare custom tableview cell? What Is The Use Of dequeuereusablecellwithidentifier ?

Ans : 

Let's create custom cell :

1. Take viewcontroller or tableviewcontroller
2. In Tableview, put one uitableviewcell and change style to custom.
3. Give any string (i.e "newcell") to reuseidentifier of cell in attribute inspector.
4. Put labels, textfields, views in cell according to your need.
5. Add new file named as newCell.swift that inherit from UITableViewCell.
6. Select your cell and give class name newCell.
7. Now you can make outlet of that cell in newCell.swift.

Here magic will be created using dequeuereusablecellwithidentifier : 

The best part of using dequeueReusableCellWithIdentifier is that using this you can re-use your cells.

Imagine if your table has 1000 entries. Now, if for each entry a table cell would be created then for 1000 entries, 1000 tableview cells and memory allocation for 1000 tableview cells.

App will be slowed down or would crash if the entries goes beyond 1000.

When we use, dequeueReusableCellWithIdentifier, the tableView just creates exactly the number of cells based on your table height and cell height. Suppose, if it shows 4 cells in the tabelView and rest you can see by scrolling, then memory for only 4 cells would be allocated at any given point of time.

Now, when you will scroll the tableView, it will re-use the same cell but will change the cell content (data) based on your data source.

Hope this clears your doubt.

Code

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    UITableViewCell *cell =[tableView dequeueReusableCellWithIdentifier:"newcell"];
    cell.textLabel.text = @"Test";
    return cell;

}

What is safe area?

Ans: The Safe Area Layout Guide helps avoid underlapping System UI elements when positioning content and controls.

The Safe Area is the area in between System UI elements which are Status Bar, Navigation Bar and Tool Bar or Tab Bar. So when you add a Status bar to your app, the Safe Area shrink. When you add a Navigation Bar to your app, the Safe Area shrinks again.

On the iPhone X, the Safe Area provides additional inset from the top and bottom screen edges in portrait even when no bar is shown. In landscape, the Safe Area is inset from the sides of the screens and the home indicator.

The layout guide (Safe area) representing the portion of your view that is unobscured by bars and other content. In iOS 11+, Apple is deprecating the top and bottom layout guides and replacing them with a single safe area layout guide.

In iPhone X portrait, safe area insets from top(notch) and bottom(home) side, and
in landscape, left(notch/ home bar) and right side(home bar/notch) and also bottom side.

We can enable using of safe area layout guide property of view controller from class inspector.

Difference Between UIWindow And UIView?

Ans :

Windows do not have any visible content themselves but provide a basic container for your application’s views. 

Views define a portion of a window that you want to fill with some content. 

Note : Typically, there is only one window in an iOS application.

What method is called after tap back button in ios?

Ans : 

When you go back the following methods will be called:

Notifies the view controller that its view is about to be added to a view hierarchy : 

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
}


Notifies the view controller that its view was added to a view hierarchy : 

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)

}

How many ways to pass data from one view controller to another view controller?

Ans :

Through following methods, we can pass data from one viewcontroller to another viewcontroller.

1. Using segue (PrepareForSegue) method,
2. Delegate
3. Setting variable

Let's assume we have 2 viewcontroller named VC1 and VC2. We want to pass data from VC1 to VC2 and some times VC2 to VC1. For both cases, we can use segue to pass data. But in general practise, to pass data from VC1 to VC2 (Forward data passing), we use segue and from VC2 to VC1(Backward data passing), we use protocol - delegate way.

1. Using segue (PrepareForSegue) steps :  VC1 --->  VC2

•   Draw segue from VC1 to VC2 and give identifier string 'InputVCToDisplayVC'  to segue.
•   Take variable in VC2.swift as :

           var fullName : String?

•    In VC1, write following code in PrepareForSegue method,

       override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if(segue.identifier == "InputVCToDisplayVC"){
let displayVC = segue.destination as! DisplayViewController
displayVC.fullName = nameTextField.text
        }
        }

•       In VC2, viewDidLoad, we can get  value of fullName and access it.

2. Using delegate steps :    VC2  --->  VC1

Import UIKit

class VC1: UIViewController, VC2Delegate {

       override func viewDidLoad() {

                super.viewDidLoad()

                

       }

       func doSomething(data : String) {

                print(data)

      }

      override func prepare(for segue: UIStoryboardSegue, sender: Any?) {

      if(segue.identifier == "InputVCToDisplayVC"){

      let displayVC = segue.destination as! DisplayViewController

      displayVC.delegate = self

      }

       }

 }

Import UIKit

protocol VC2Delegate {

      func doSomething(data : String) 

}

class VC2 : UIViewController {

        

      var fullName : String?

      weak var delegate : VC2Delegate?

      

      override func viewDidLoad() {

             

     }

     @IBAction func btnPassToVC1_TouchUpInside(_ sender : UIButton) {

              if let delegate = delegate {

                     delegate.doSomething(data: btn.titleLabel.text)       

              }

    }

}

In above, method we make custom protocol and create its object as delegate.We set delegate reference to VC1. So on VC2 button pressed event, VC1 doSomething method will be called.

3. Setting Variable steps :     VC1   --->  VC2

• Take variable in VC2.swift as :  

           var fullName : String?

• On buttonPressed action of VC1, write code as :

           let vc2 : VC2 =  UIStoryboard(name: "Main", bundle:                                                                                                        nil).instantiateViewController(withIdentifier: "VC2_ID") as! VC2

           vc2.fullName = "iOS iQA"

           self.present(vc2, animated: true, completion: nil)

Note : There are also persistent storage, by which we can store data and access that data any where in our project. But this is not correct answer or solution for above question or problem. We can store data in NSUserDefault, PList, Coredata, SQLite, KeyChain Access, File as persistent storage.

    

Do you like to use storyboard? Why? Can more than 1 storyboard allowed?

Ans : I like to use storyboard.

I am using storyboard due to advantage over XIB : See here

Yes, we can use more than 1 storyboard. We can make different storyboard for different features in same project.

Navigating from one storyboard to another storyboard :

1. Using segue :

• Drag & Drop storyboard reference
• Give name and assign viewcontroller (to which we want to navigate)
• Give segue from viewcontroller to storyboard reference.

2. Using coding :

var anotherStoryboard = UIStoryboard(name: "another", bundle: nil)

var vc: UIViewController = anotherStoryboard.instantiateViewController(withIdentifier: "loginView")

present(vc, animated: false)

What is multiplier and ratio in auto layout in ios?

Ans :


Difference between Multiplier and Ratio : 

There is not any difference. Both are using for same purpose.

The Aspect Ratio is really just a convenient way to express the Multiplier when working in Interface Builder. It effectively gets "converted" to a multiplier.

You can confirm this while debugging by inspecting the constraint's .multiplier property. If you set a view's width to 60, and multiplier to 1:2 (resulting in an auto-layout height of 120), the actual value of .multiplier will be 0.5.

So, in my view, it depends on what feels more natural.

If I want a view to be 90% of the width of another view, I am much more likely to set the Multiplier to 0.9 --- which gives the exact same result as setting it to 9:10.

However, if I want a view to maintain an aspect ration of, say, 3-to-2, I am much more likely to set the Multiplier to 3:2 rather than 1.5.

Using a ratio can also be convenient when you have "non-simple" values. That is, it's easy to understand that a ratio of 3:2 is the same as 1.5. But what if I have an image with native size of 281 x 60, and I want to use those values to maintain ratio? 281:60 is easier to understand than .multiplier = 4.68333339691162.

And, while they are interchangeable, it is probably a bit more intuitive to use Ratio when constraining an object to itself - e.g. I want my view's width to be 2 x its own height, so 2:1 - and using Multiplier when constraining one object to another - e.g. I want my view's width to be 75% of the width of its superview, so 0.75.

Design such button in that text should be displayed below image

Ans : 

1) Select button and go to Attribute Inspector in your storyboard.

2) Assign Image to the button. (Don't use background Image)

3) Set Title text to that button.

4) Now you need to set edge and Inset so first select image from edge and set Inset as you need and then select title from edge and set inset as per your need.

Difference between XIB and Storyboard

Ans : 


XIB :

1) Xib files are used with a single UIView.

3)It's utilizes more memory as compared to storyboard and quiet slow.

4) It is compatible from iOS5 and onwards

5) You can do localizations for different languages and countries using different XIBs .

6) It's difficult to use same Xib to support multiple devices.

Storyboard :

1)You can layout all your Scenes like View Controllers, Nav Controllers, TabBar Controllers, etc in a single storyboard.

3)Usually fast and allocates less memory.

4)It's not compatible prior to iOS 5 .

5)"Dynamic" and "Prototype" cells can be used easily.

6)Storyboards best to use for the apps with a small to medium amount of screens.

What is size class? Explain with Example.

Ans : 
Size Classes are groups of screen sizes that are applied to the width and height of the device screen. The two Size Classes that exist currently are Compact and Regular.

The Compact Size Class refers to a constrained space. It is denoted in Xcode as wC (Compact width) and hC (Compact height).

The Regular Size Class refers to a non-constrained space. It is denoted in Xcode as wR (Regular width) and hR (Regular height).

iPhone : Most iPhone devices will use the Compact width (wC) size class in each orientation with some exceptions.
The iPhones 6/7 Plus can inherit the Regular width (wR) size class resulting in the ability to use functionality normally reserved for the iPad, such as the split-view pane. Split-VIew pane is speciall made for iPad.

iPad : All iPad devices use the Regular width (wR) size class regardless of landscape or portrait orientation. In both horizontal and vertical landscape, the iPad will use a split-view pane to take advantage of the available screen space because it falls within this unconstrained size class.

Controlling the UI with Size Classes

In most cases, specifying the width class is sufficient when laying out your app; however, you can use the height class to customize your app as well. For example, if you use a split-view pane in an iPad app, users will see the same pane on iPhone Plus in landscape orientation because they both inherit the Regular width (wR) size class.

If that is not your intention, you can exclude a split-view pane from appearing on the 7 Plus by specifying both the width and height Size Classes. This works because the height of an iPhone Plus in landscape orientation is compact (hC) while all iPad devices have a regular height (hR).

You can also use Size Classes to target specific UI elements like font colors, font sizes, drop shadows, view colors and more to adapt to users’ device screen. These variations give you added control as to how your UI can adapt to different devices and orientations that your user may be using.

Difference between frames and bounds.

Ans : 

Frame :  View's location and size using the parent view's coordinate system
Needed while placing the view in the parent

bounds = View's location and size using its own coordinate system
Needed while placing the view's content or subviews within itself

The bounds of an UIView is the rectangle, expressed as a location (x,y) and size (width,height) relative to its own coordinate system (0,0).

The frame of an UIView is the rectangle, expressed as a location (x,y) and size (width,height) relative to the superview it is contained within.

So, imagine a view that has a size of  50x50 (width x height) positioned at 15,15 (x,y) of its superview. The following code prints out this view's bounds and frame:

NSLog(@"bounds.origin.x: %f", label.bounds.origin.x);
NSLog(@"bounds.origin.y: %f", label.bounds.origin.y);
NSLog(@"bounds.size.width: %f", label.bounds.size.width);
NSLog(@"bounds.size.height: %f", label.bounds.size.height);

NSLog(@"frame.origin.x: %f", label.frame.origin.x);
NSLog(@"frame.origin.y: %f", label.frame.origin.y);
NSLog(@"frame.size.width: %f", label.frame.size.width);
NSLog(@"frame.size.height: %f", label.frame.size.height);

Output : 

bounds.origin.x: 0
bounds.origin.y: 0
bounds.size.width: 50
bounds.size.height: 50

frame.origin.x: 15
frame.origin.y: 15
frame.size.width: 50
frame.size.height: 50

So, we can see that in both cases, the width and the height of the view is the same regardless of whether we are looking at the bounds or frame. What is different is the x,y positioning of the view. In the case of the bounds, the x and y coordinates are at 0,0 as these coordinates are relative to the view itself. However, the frame x and y coordinates are relative to the position of the view within the parent view (which earlier we said was at 25,25).

For more understanding : Visit this 

What is StackView? What is advantage and distribution type of stackview?

Ans : Stack View allows to layout views in a stack in either horizontal or vertical fashion. In Xcode-7, stackview is introduced.

Advantage : Stacks are containers that keep views aligned automatically.

Distribution Types :

Fill(Default) : When you place your controls inside a UIStackView with Fill set as the distribution, it will keep all but one of the controls at their natural size and stretch one of them to fill the space. It determines which control to stretch by noting which one has the lowest Content Hugging Priority (CHP).

Fill Equally : With this type, each control in a UIStackView will be of equal size. All of the space between the controls will be used up, if possible. I added a spacing of eight between the UITextFields, so again you could see the size of each one. With this type, the CHP does not matter, because each control is the same size.

Fill Proportionally : The UIStackView will ensure the controls maintain the same proportion relative to one another as your layout grows and shrinks. Unlike the previous two settings, the Fill Proportionally distribution needs the controls to have an intrinsic content size. The Fill and Fill Equally distribution tell their child controls how big they should be, but this one is the other way around (as long as there is enough space for all of your controls to be their natural size). The proportions for the images and labels are maintained for the different layout sizes.

Equal Spacing : This distribution type will maintain an equal spacing between each of the controls and will not resize the controls themselves.

Equal Centring :  It will equally space the centres of the controls. Space between every control is equal.