[iOS] UITableView 内对应复杂 DataSource(富文本内容)展现框架

CascadingTableDelegate A no-nonsense way to write cleaner UITableViewDelegateand UITableViewDataSource


A no-nonsense way to write cleaner UITableViewDelegateand UITableViewDataSource.

Why is this library made?

In common iOS development, UITableViewhas became the bread and butter for building rich pages with repetitive elements. This page, for example:

[iOS] UITableView 内对应复杂 DataSource(富文本内容)展现框架

(Kudos to Wiekyfor helping me creating this sample page's design! :grin:)

Still, using UITableViewhas its own problems.

As you know, to display the contents, UITableViewuses UITableViewDelegateand UITableViewDataSource- compliant objects. This often became the cause of my headache since UITableView only allows one objectto become the delegateand dataSource. These limitations might lead to an unnecessarily huge source code file - caused by know-it-all Megamoth methods. Some common victims of this problem are tableView(_:cellForRowAt:), tableView(_:heightForRowAt:), and tableView(_:didSelectRowAt:).

Because of this, there are times when I thought it be nice if we could splitthe delegateand dataSourcemethod calls into each section or row.

Meet CascadingTableDelegate.

CascadingTableDelegateis an approach to break down UITableViewDelegateand UITableViewDataSourceinto tree structure, inspired by the Composite pattern. Here's the simplified structure of the protocol (with less documentation):

public protocol CascadingTableDelegate: UITableViewDataSource, UITableViewDelegate { /// Index of this instance in its parent's `childDelegates`. Will be set by the parent. var index: Int { get set } /// Array of child `CascadingTableDelegate` instances. var childDelegates: [CascadingTableDelegate] { get set } /// Weak reference to this instance's parent `CascadingTableDelegate`. weak var parentDelegate: CascadingTableDelegate? { get set } /** Base initializer for this instance. - parameter index: `index` value for this instance. May be changed later, including this instance's `parentDelegate`. - parameter childDelegates: Array of child `CascadingTableDelegate`s. - returns: This class' instance. */ init(index: Int, childDelegates: [CascadingTableDelegate]) /** Preparation method that will be called by this instance's parent, normally in the first time. - note: This method could be used for a wide range of purposes, e.g. registering table view cells. - note: If this called manually, it should call this instance child's `prepare(tableView:)` method. - parameter tableView: `UITableView` instance. */ func prepare(tableView tableView: UITableView)}

Long story short, this protocol allows us to propagateany UITableViewDelegateor UITableViewDataSourcemethod call it receives to its child, based on the sectionor rowvalue of the passed IndexPath.

But UITableViewDelegate and UITableViewDataSource has tons of methods! Who will propagate all those calls?

Worry not, this library did the heavy lifting by creating two ready-to-use classes, CascadingRootTableDelegateand CascadingSectionTableDelegate. Both implements CascasdingTableDelegateprotocol and the propagating logic, but with different use case:

  • CascadingRootTableDelegate:

    • Acts as the main UITableViewDelegateand UITableViewDataSourcefor the UITableView.
    • Propagates almostall of delegate and dataSource calls to its childDelegates, based on sectionvalue of the passed IndexPathand the child's index.
    • Returns number of its childDelegatesfor numberOfSections(in:)call.
  • CascadingSectionTableDelegate:

    • Does not sets itself as UITableViewDelegateand UITableViewDataSourceof the passed UITableView, but waits for its parentDelegatemethod calls.
    • Just like CascadingRootTableDelegate, it also propagates almostall of delegate and dataSource calls to its childDelegates, but based by the rowof passed IndexPath.
    • Returns number of its childDelegatesfor tableView(_:numberOfRowsInSection:)call.

Here's a diagram to potray how a tableView(_:cellForRowAt:)call works to those classes:

[iOS] UITableView 内对应复杂 DataSource(富文本内容)展现框架

Both classes also accepts your custom implementations of CascadingTableDelegate(which is only UITableViewDataSourceand UITableViewDelegatewith few new properties and methods, really) as their childDelegates. Plus, you could subclass any of them and call superon the overriden methods to let them do the propagation - Chain-of-responsibility-esque style :wink:

Here's a snippet how the long page above is divided into section delegates in the sample code:

[iOS] UITableView 内对应复杂 DataSource(富文本内容)展现框架

All the section delegate classes then added as childs to a single CascadingRootTableDelegate. Any change on the sequence or composition of its childDelegateswill affect the displayed table. Clone this repo and try it out in sample project! :grin:

Pros and Cons


With CascadingTableDelegate, we could:

  • Break down UITableViewDataSourceand UITableViewDelegatemethods to each section or row, resulting to cleaner, well separated code.
  • Use the familiar UITableViewDataSourceand UITableViewDelegatemethods that we have been used all along, allowing easier migrations for the old code.

Other pros:

  • All implemented methodson CascadingRootTableDelegateand CascadingSectionTableDelegateare unit tested! To run the tests, you could:
    • Open the sample project and run the available tests, or
    • Execute run_tests.shin your terminal.
  • This library is available through Cocoapods and Carthage! :wink:


1. Unpropagated special methods

As you know, not all UITableViewDelegatemethod uses single IndexPathas their parameter, which makes propagating their calls less intuitive. Based on this reasoning, CascadingRootTableDelegateand CascadingSectionTableDelegatedoesn't implement these UITableViewDelegatemethods:

  • sectionIndexTitles(for:)
  • tableView(_:sectionForSectionIndexTitle:at:)
  • tableView(_:moveRowAt:to:)
  • tableView(_:shouldUpdateFocusIn:)
  • tableView(_:didUpdateFocusInContext:with:)
  • indexPathForPreferredFocusedView(in:)
  • tableView(_:targetIndexPathForMoveFromRowAt: toProposedIndexPath:)

    Should you need to implement any of those, feel free to subclass both of them and add your own implementations! :grin:

2. tableView(_:estimatedHeightFor...:)method handlings

There are three optional UITableViewDelegatemethods that used to estimate heights:

  • tableView(_:estimatedHeightForRowAt:),
  • tableView(_:estimatedHeightForHeaderInSection:), and
  • tableView(_:estimatedHeightForFooterInSection:).

CascadingRootTableDelegateand CascadingSectionTableDelegateimplements those calls for propagating it to the childDelegates. And since both of them implements those, the UITableViewwill alwayscall those methods when rendering its rows, headers, and footers.

To prevent layout breaks, CascadingRootTableDelegateand CascadingSectionTableDelegatewill call its childDelegate's tableView(_:heightFor...:)counterpart for the unimplemented methods, so the UITableViewwill render it correctly. If your tableView(_:heightFor...:)methods use heavy calculations, it is advised to implement the tableView(_:estimatedHeightFor...:)counterpart of them.

Should both method not implemented by the childDelegate, CascadingRootTableDelegateand CascadingSectionTableDelegatewill return UITableViewAutomaticDimensionfor tableView(_:estimatedHeightForRowAt:), and 0for tableView(_:estimatedHeightForHeaderInSection:)and tableView(_:estimatedHeightForFooterInSection:).

For details of every method's default return value (that has one), please refer to the Default Return Value documentation.

3. weakdeclaration for parentDelegate

Somehow, Xcode won't add weakmodifier when you're implementing your own CascadingTableDelegateand autocompleting the parentDelegateproperty. Kindly add the weakmodifier manually to prevent retain cycles :grin:

Still, if you still think typing it manually is a tedious job, just subclass the CascadingBareTableDelegateout. It's a bare implementation of the CascadingTableDelegate, without the propagating logic ��


To run the example project, clone the repo, and run pod installfrom the Example directory first.


This version supports Swift 3, which available in Xcode 8. For Swift 2.2 / Xcode 7.x support, kindly check the 1.x versions ��



To install CascadingTableDelegate using CocoaPods, simply add the following line to your Podfile:

pod "CascadingTableDelegate", "~> 2.0"


To install CascadingTableDelegate usingCarthage, simply add the following line to your Cartfile:

github "edopelawi/CascadingTableDelegate" ~> 2.0


Ricardo Pramana Suranta, ricardo.pramana@gmail.com


CascadingTableDelegate is available under the MIT license. See the LICENSE file for more info.