How to implement a list with a large number of cells in iOS?

UITableView or UICollectionView are used to display large lists. They implement the cell reuse pattern, which allows efficient memory and performance management.

Main steps:

1. Create a UITableView or UICollectionView: Place an instance of the respective class on the screen.

2. Assign DataSource and Delegate: Set the controller or another object as dataSource and delegate.

   // Example for UITableView
   tableView.dataSource = self 
   tableView.delegate = self
   

   • dataSource is responsible for providing data for the list (number of sections/rows, cell content).
   • delegate handles interaction events with cells (selection, swipes, etc.) and appearance customization.

3. Register cells: Register cell classes (UITableViewCell or UICollectionViewCell) for reuse. You can use classes or nib files.

   // Example of registering a custom UITableViewCell class
   tableView.register(MyCustomCell.self, forCellReuseIdentifier: "MyCellIdentifier")
   
   // Example of registering a custom UITableViewCell from nib
   tableView.register(UINib(nibName: "MyCustomCell", bundle: nil), forCellReuseIdentifier: "MyCellIdentifier")
   

4. Implement dataSource methods: Mandatory methods for UITableViewDataSource:

   • numberOfSections(in:): Returns the number of sections.
   • tableView(_:numberOfRowsInSection:): Returns the number of rows in a section.
   • tableView(_:cellForRowAt:): Key method for reuse. Requests a cell from the pool.

   // Example implementation of tableView(_:cellForRowAt:)
   func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
       // Get a cell from the reuse pool
       guard let cell = tableView.dequeueReusableCell(withIdentifier: "MyCellIdentifier", for: indexPath) as? MyCustomCell else {
           fatalError("Unable to dequeue MyCustomCell") // Error handling
       }
       
       // Configure cell content based on data
       let item = data[indexPath.row] // Assuming a data array
       cell.configure(with: item) // Example of cell configuration method
       
       return cell
   }
   

5. Implement delegate methods (optional): For example, to handle cell selection:

   // Example of handling cell selection
   func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
       let selectedItem = data[indexPath.row]
       // Perform action with selected item
       print("Selected: \(selectedItem)")
   }
   

Cell reuse principle:

iOS maintains a pool of cells that are no longer visible on the screen. When a new cell needs to be displayed (e.g., during scrolling), instead of creating a new one, the system reuses a cell from this pool. The method dequeueReusableCell(withIdentifier:for:) requests such a cell. This significantly saves memory and computational resources.

UICollectionView:

Works similarly to UITableView but offers greater flexibility in layout (grids, custom layouts). It requires implementation of UICollectionViewDataSource and UICollectionViewDelegate. Instead of rows and cells, it operates with items and sections.

Using UITableView or UICollectionView with cell reuse is the standard and most efficient way to display large lists in iOS.