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iOS Apprentice

Eighth Edition · iOS 13 · Swift 5.2 · Xcode 11

Getting Started with SwiftUI

Section 1: 8 chapters
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Section 2: 6 chapters
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Getting Started with UIKit

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Store Search

Section 5: 13 chapters
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23. Edit High Score Screen
Written by Eli Ganim

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Now that you have the navigation flow from your main screen to the Edit High Score screen working, it’s time to actually implement the edit functionality for this screen!

Let’s change the look of the Edit screen. Currently, it is an empty table with a navigation bar on top — but it’s going to look like this:

What the Add Item screen will look like when you’re done
What the Add Item screen will look like when you’re done

This chapter covers the following:

  • Static table cells: Add a static table view cell to the table to display the text field for data entry.
  • Read from the text field: Access the contents of the text field.
  • Polish it up: Improve the look and functionality of the Edit High Score screen.

Static table cells

First, you need to add a table view cell to handle the data input for the Edit High Score screen. As is generally the case with UI changes, you start with the storyboard.

Storyboard changes

➤ Open the storyboard and select the Table View object inside the Edit High Score scene.

Changing the table view to static cells
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The table view has a section with three static cells
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The table view with grouped style
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Adding a text field to the table view cell
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Disabling cell selection

Look what happens when you tap just outside of the text field’s area but still in the cell. Try tapping in the margins that surround the text field:

Whoops, that looks a little weird
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// MARK:- Table View Delegates
override func tableView(_ tableView: UITableView, 
          willSelectRowAt indexPath: IndexPath) 
          -> IndexPath? {
  return nil
}

Working with the text field

You have a text field in a table view cell that the user can type into. How do you populate it with the current name from the HighScoreItem? And how do you read the text that the user has typed?

Adding an outlet for the text field

You already know how to refer to controls from within your view controller: Use an outlet. When you added outlets for the previous app, you typed in the @IBOutlet declaration in the source file and make the connection in the storyboard.

Click the toolbar button to open the Assistant editor
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The Assistant editor
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Control-dragging from the text field into the Swift file
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The pop-up that lets you add a new outlet
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@IBOutlet weak var textField: UITextField!

Reading from the text field

Now, you’ll modify the done() action to write the contents of this text field to the Xcode Console, the pane at the bottom of the screen where print() messages show up. This is a quick way to verify that you can actually read what the user typed.

@IBAction func done() {
  // Add the following line
  print("Contents of the text field: \(textField.text!)")

  navigationController?.popViewController(animated: true)
}

Contents of the text field: Hello, world!

Polishing it up

Before you write the code to take the text and update the high score item, let’s improve the design and workings of the Edit High Score screen a little.

Giving the text field focus on-screen opening

For instance, it would be nice if you didn’t have to tap on the text field to bring up the keyboard. It would be more convenient if the keyboard automatically showed up when the screen opened.

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

Styling the text field

With that in mind, let’s style the input field a bit.

The text field attributes
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Handling the keyboard Done button

➤ Make sure the text field is selected and open the Connections inspector. Drag from the Did End on Exit event to the view controller and pick the done action.

Connecting the text field to the done() action method
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Viewing the connections for the done() method
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The keyboard now has a big blue Done button
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Disallowing empty input

Now that you have user input working, It’s always good to validate what the user entered to make sure that the input is acceptable. For instance, what should happen if the user taps the Done button on the Edit High Score screen without entering any text?

The Auto-enable Return Key option disables the return key when there is no text
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Becoming a delegate

Delegates are used everywhere in the iOS SDK, so it’s good to remember that it always takes three steps to become a delegate:

class EditHighScoreViewController: UITableViewController, UITextFieldDelegate {
Drag from the Connections inspector to connect the text field delegate
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Configuring the Done button

You also have to add an outlet for the Done bar button item so you can send it messages from within the view controller to enable or disable it.

@IBOutlet weak var doneBarButton: UIBarButtonItem!

// MARK:- Text Field Delegates
func textField(_ textField: UITextField, 
               shouldChangeCharactersIn range: NSRange, 
               replacementString string: String) -> Bool {

  let oldText = textField.text!    
  let stringRange = Range(range, in: oldText)!
  let newText = oldText.replacingCharacters(in: stringRange, 
                                          with: string)
  if newText.isEmpty {
    doneBarButton.isEnabled = false
  } else {
    doneBarButton.isEnabled = true
  }
  return true
}

let oldText = textField.text!
let stringRange = Range(range, in:oldText)!
let newText = oldText.replacingCharacters(in: stringRange, with: string)

NSRange vs. Range and NSString vs. String

In the above code, you get a parameter as NSRange and you convert it to a Range value. If you’re wondering what a range is, the clue is in the name. A range object gives you a range of values. Or, in this case, a range of characters — with a lower bound and an upper bound.

if newText.isEmpty {
  doneBarButton.isEnabled = false
} else {
  doneBarButton.isEnabled = true
}

doneBarButton.isEnabled = !newText.isEmpty

if some condition {
  something = true
} else {
  something = false
}

something = (some condition)
22. Navigation Controllers
24. Delegates & Protocols
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