Add Section About Extensions (freeCodeCamp#23428)

guide/english/swift/view-controller/index.md

@@ -20,4 +20,66 @@ This is an example of what a basic view in Swift looks like.
  ```
 1. Loads view after the controller loads.
 2. Overrides the UIViewController class. This is a necessary step for any view controller.
-3. Sets background color to white.
+3. Sets background color to white.
+
+## Extending View Controllers
+
+Extensions can help keep your code clean when conforming to multiple protocols.
+
+This is an example of how you can add a TableView to a Basic View Controller.
+
+```Swift
+  import UIKit
+
+  class ViewController: UIViewController {
+      // 1
+      @IBOutlet weak var tableView: UITableView!
+
+      // 2
+      let data = ["New York, NY", "Los Angeles, CA", "Chicago, IL", "Houston, TX",
+        "Philadelphia, PA", "Phoenix, AZ", "San Diego, CA", "San Antonio, TX",
+        "Dallas, TX", "Detroit, MI", "San Jose, CA", "Indianapolis, IN",
+        "Jacksonville, FL", "San Francisco, CA", "Columbus, OH", "Austin, TX",
+        "Memphis, TN", "Baltimore, MD", "Charlotte, ND", "Fort Worth, TX"]
+
+      override func viewDidLoad() {
+          super.viewDidLoad()
+
+          // 10
+          tableView.dataSource = self
+          // 11
+          tableView.register(UITableViewCell.self, forCellReuseIdentifier: "myCellIdentifier")
+      }  
+  }
+
+  // 3
+  extension ViewController: UITableViewDataSource {
+
+      // 4
+      func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
+          // 5
+          let cell = tableView.dequeueReusableCell(withIdentifier: "myCellIdentifier", for: indexPath)
+          // 6
+          cell.textLabel?.text = data[indexPath.row]
+          // 7
+          return cell
+      }
+
+      // 8
+      func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
+          // 9
+          return data.count
+      }
+  }
+```
+1. Define the outlet for our tableView
+2. Define the data that we'll be loading into our tableView
+3. Adds extension to ViewController class that conforms to UITableViewDataSource
+4. Implement the UITableViewDataSource stubs for required methods - cellForRowAt (defines what goes in a specific cell)
+5. Define a cell as a resuable element with the identifier "myCellIdentifier"
+6. Provide our cell's textLabel with the referenced data
+7. Return that cell
+8. Implement the UITableViewDataSource stubs for required methods - numberOfRowsInSection (defines how many rows will be in your tableView)
+9. Return the size of our data array
+10. Set the tableView's dataSource to self when the view loads
+11. register the tableView's cell