Creating Complex Lists in Your List Screenlet

Most list Screenlets’ Themes use iOS’s UITableView to display simple lists. Although UITableView is great for this, it’s not so great for complex lists like grids or stacks. To create complex lists, you should use iOS’s UICollectionView in your list Screenlet’s Theme.

This tutorial shows you how to create such a Theme, using the sample Bookmark List Screenlet’s Collection Theme as an example. First, you’ll create the list’s cell.

Creating the Cell

You’ll create your list’s cell with the same sequence of steps used to create any list Screenlet’s cell. Note, however, that how you perform these steps is a bit different:

  1. Define your cell’s UI in a new XIB file. Because this cell is part of a Theme that uses UICollectionView, you can shape it however you want. For example, here’s the BookmarkCell_default-collection.xib file for the cell in Bookmark List Screenlet’s Collection Theme. It’s a simple square that displays the bookmark’s URL and the URL’s first letter.

    Figure 1: The XIB file for the cell in Bookmark List Screenlets custom View.

    Figure 1: The XIB file for the cell in Bookmark List Screenlet's custom View.

  2. Create your XIB file’s class by extending UICollectionViewCell. Create as many outlets and actions as you need for your UI components and write the logic required for your cell’s UI to function. For example, BookmarkCell_default_collection is the XIB file’s class in Bookmark List Screenlet’s Custom Theme. This class extends UICollectionViewCell and contains outlets for the URL (urlLabel) and the URL’s first letter (centerLabel). The bookmark variable’s didSet observer sets the bookmark’s name and URL to the respective label. Also note that the overridden prepareForReuse method resets the labels for reuse:

    import UIKit
    import LiferayScreens
    public class BookmarkCell_default_collection: UICollectionViewCell {
        //MARK: Outlets
        @IBOutlet weak var centerLabel: UILabel?
        @IBOutlet weak var urlLabel: UILabel?
        //MARK: Public properties
        public var bookmark: Bookmark? {
            didSet {
                if let bookmark = bookmark, url = NSURL(string: bookmark.url),
                    firstLetter ="www.").characters.first {
                        self.centerLabel?.text = String(firstLetter).uppercaseString
                        self.urlLabel?.text = bookmark.url.remove("http://").remove("https://").remove("www.")
        //MARK: UICollectionViewCell
        override public func prepareForReuse() {
            centerLabel?.text = "..."
            urlLabel?.text = "..."

Now that your cell exists, you can create the rest of your Theme.

Creating the Theme’s XIB and View Class

You’ll create the rest of your Theme with the same sequence of steps used to create any list Screenlet’s Theme. Like creating the cell, how you perform these steps is a bit different because your Theme uses UICollectionView instead of UITableView.

First, define your Theme’s UI in a new XIB file. Add a UICollectionView instead of a UITableView to this file. For example, the BookmarkListView_default-collection.xib file for Bookmark List Screenlet’s Custom Theme contains a collection view.

Next, create the View class. Instead of extending BaseListTableView, this class must extend Screens’s BaseListCollectionView class. The BaseListCollectionView class implements most of the code necessary to use UICollectionView in your Screenlet. By extending it, you can focus on the code unique to your Screenlet. Your View class should also contain a string constant to serve as the cell ID. You’ll use this constant when you register your cell. For example, the View class in Bookmark List Screenlet’s Collection Theme (BookmarkListView_default_collection) extends BaseListCollectionView and defines the string constant BookmarkCellId:

public class BookmarkListView_default_collection : BaseListCollectionView {

    let BookmarkCellId = "bookmarkCell"

In Interface Builder, set this new class as the XIB’s Custom Class.

Next, override the doRegisterCellNibs method to register the cell you created in the previous section. In this method, create a UINib instance for your cell and then register it with the UICollectionView instance (collectionView) inherited from BaseListCollectionView. When registering the nib file, you must use the string constant you created earlier as the forCellReuseIdentifier. For example, here’s the doRegisterCellNibs method in BookmarkListView_default_collection:

public override func doRegisterCellNibs() {
    let cellNib = UINib(nibName: "BookmarkCell_default-collection", bundle: nil)
    collectionView?.registerNib(cellNib, forCellWithReuseIdentifier: BookmarkCellId)

Also in your View class, override the doGetCellId method to return the ID you registered the cell with. For example, the doGetCellId method in BookmarkListView_default_collection returns the string constant BookmarkCellId:

public override func doGetCellId(indexPath indexPath: NSIndexPath, object: AnyObject?) -> String {
    return BookmarkCellId

Next, override the doFillLoadedCell method to fill the cell with data. This method’s object argument contains the data as AnyObject. You must cast this to your desired type and then set it to the appropriate cell variable. For example, the doFillLoadedCell method in BookmarkListView_default_collection casts the object argument to Bookmark and then sets it to the cell’s bookmark variable:

public override func doFillLoadedCell(
        indexPath indexPath: NSIndexPath,
        cell: UICollectionViewCell,
        object: AnyObject) {

    if let cell = cell as? BookmarkCell_default_collection, bookmark = object as? Bookmark {
        cell.bookmark = bookmark

Next, you’ll create the layout.

Creating the Layout

The layout object is a key part of UICollectionView. This object controls the position of the UI elements, their size, and more. To customize the layout object, override the doCreateLayout method in your View class. For example, the doCreateLayout method in Bookmark List Screenlet’s View class (BookmarkListView_default_collection) returns a UICollectionViewFlowLayout for the layout object. This is a basic layout that gives you a simple way to customize things like item size, spacing between items, scroll direction, and more:

public override func doCreateLayout() -> UICollectionViewLayout {
    let layout = UICollectionViewFlowLayout()
    layout.itemSize = CGSize(width: 110, height: 110)
    layout.minimumLineSpacing = 10
    layout.minimumInteritemSpacing = 10

    return layout

Great! You’re done! You can now use your new Theme the same way you would any other.

If you want to package your Theme to contribute it to the Liferay Screens project or distribute it with CocoaPods, see the tutorial on packaging Themes.

Creating iOS List Screenlets

Creating iOS Themes

Sorting Your List Screenlet

Using Custom Cells with List Screenlets

iOS Best Practices

« Sorting Your List ScreenletCreating iOS Themes »
Was this article helpful?
0 out of 0 found this helpful