This document discusses improving table view data sources by implementing the single responsibility principle and using combinators. It outlines problems with traditional approaches where view controllers handle data sources and cells. The author advocates defining base data source classes that provide minimal functionality and combining them to add dynamic behaviors like filtering, reordering and indexing. Implementing this approach removes duplicate code, allows changing behavior through combinators, and makes data sources reusable across views. Examples of combinators that could be implemented are provided.

1. Data$Source$Combinators
©"Robert"Brown"March"2015"@robby_brown

2. Table&Views
you're'doing'them'wrong
©"Robert"Brown"March"2015"@robby_brown

3. Overview
1. The&Hard&Way
2. Code&Architecture&Theory
3. The&Be7er&Way
©"Robert"Brown"March"2015"@robby_brown

4. Demo
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5. The$Hard$Way
©"Robert"Brown"March"2015"@robby_brown

6. Cell$Crea'on
class CandyTableViewController : UITableViewController {
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return self.candies.count
}
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = self.tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath) as UITableViewCell
let candy = self.candies[indexPath.row]
cell.textLabel!.text = candy.name
cell.accessoryType = UITableViewCellAccessoryType.DisclosureIndicator
return cell
}
}
From:&raywenderlich.com
©"Robert"Brown"March"2015"@robby_brown

7. Cell$Crea'on
What's'wrong'with'this?
• Duplicate+boilerplate
• View+controllers+handle+interac5on,+not+data+sources
• Cells+are+o8en+shared+between+table+views
• Cells+should+handle+their+own+layout
©"Robert"Brown"March"2015"@robby_brown

8. Cell$Crea'on
Why$do$we$see$this$so$o,en?
• It's&"standard"&prac.ce
• That's&how&I've&always&done&it
• My&favorite&tutorial&does&it
• Apple&does&it
©"Robert"Brown"March"2015"@robby_brown

9. Cell$Crea'on
Why$do$we$see$this$so$o,en?
• It's&really&convenient&for&tutorials&to&be&simple
©"Robert"Brown"March"2015"@robby_brown

10. Code%Architecture%Theory
©"Robert"Brown"March"2015"@robby_brown

11. Data$Sources
Problems:
• Massive(View(Controller
• Duplicate(boilerplate
©"Robert"Brown"March"2015"@robby_brown

12. Data$Sources
Solu%on:
• Single(responsibility0principle
• Combinators
• Chain(of(responsibility
©"Robert"Brown"March"2015"@robby_brown

13. A"class"should"have"only"one"reason"
to"change.
—"Single)responsibility"principle
©"Robert"Brown"March"2015"@robby_brown

14. A"class"should"have"only"one"reason"
to"change.
—"Single)responsibility"principle
©"Robert"Brown"March"2015"@robby_brown

15. Every&class&should&have&
responsibility&over&a&single&part&of&
the&func6onality...,&and&that&
responsibility&should&be&en6rely&
encapsulated&by&the&class.1
—"Single)responsibility"principle
1
"Wikipedia
©"Robert"Brown"March"2015"@robby_brown

16. Combinators
• Technique*from*func/onal*programming
• Usually*seen*with*parsers
• Generally*represent*a*single,*simple*feature
• Focus*on*composi/on
• Like*higher>order*func/ons*applied*to*features
©"Robert"Brown"March"2015"@robby_brown

17. Chain&of&Responsibility
• Like&a&chain&of&delegates
• A&3>&B&3>&C&3>&D&...
• If&A&can't&handle&something,&then&try&B&...
• Used&to&create&a&sequence&of&combinators
©"Robert"Brown"March"2015"@robby_brown

18. The$Be&er$Way
©"Robert"Brown"March"2015"@robby_brown

19. Cell$Crea'on
View%Controller
override func viewDidLoad() {
super.viewDidLoad()
let objects = [] // Get objects here
tableView.dataSource = BaseDataSource(objects) { (view, indexPath, object) -> Any in
return MyCell.cell(view as! UITableView, name: object as! String)
}
}
©"Robert"Brown"March"2015"@robby_brown

20. Cell$Crea'on
View%Controller
override func viewDidLoad() {
super.viewDidLoad()
let objects = [] // Get objects here
let base = BaseDataSource(objects) { (view, indexPath, object) -> Any in
return MyCell.cell(view as! UITableView, name: object as! String)
}
self.dataSource = ReorderableDataSource(base)
}
©"Robert"Brown"March"2015"@robby_brown

21. Cell$Crea'on
Cell
class MyCell: SmartTableViewCell {
@IBOutlet weak var titleLabel: UILabel!
class func cell(tableView: UITableView, name: String) -> Self {
let cell = self.cell(tableView)
cell.titleLabel.text = name
return cell
}
}
©"Robert"Brown"March"2015"@robby_brown

22. Cell$Crea'on
Why$is$this$be*er?
• Fewer&lines&of&code
• Boilerplate&removed
• Behavior&can&be&changed&with&the&data&source(s)
• The&data&source&can&work&with&table&and&collec=on&views
• Easier&to&build&combinators
©"Robert"Brown"March"2015"@robby_brown

23. Dynamic(Behaviors
• Array
• Mul)*dimensional2array
• Filtering
• Reordering
• Edi)ng
• Index2)tles
©"Robert"Brown"March"2015"@robby_brown

24. Considera*ons
• The%order%of%combinators%applied%ma4ers%for%performance
• Ex:%Create%index%9tles%before%filtering
• Some9mes%a%combinator%needs%to%implement%more%than%one%
feature%for%performance
©"Robert"Brown"March"2015"@robby_brown

25. Example(Combinators
• BaseDataSource:#Provides#minimum#func1onality
• ChainableDataSource:#Allows#data#source#sequences
• FilterableDataSource:#Allows#filtering#(ex.#search#bar)
• ReorderableDataSource:#Allows#reordering
• IndexableDataSource:#Shows#index#1tles
©"Robert"Brown"March"2015"@robby_brown

26. Demo
©"Robert"Brown"March"2015"@robby_brown

27. Summary
1. The&Hard&Way
2. Code&Architecture&Theory
3. The&Be7er&Way
©"Robert"Brown"March"2015"@robby_brown

28. Ques%ons?
©"Robert"Brown"March"2015"@robby_brown

29. Resources(to(Learn(More
• Source(Code
• Combinator
• Func2onal(Programming(in(Swi7
• Func2onal(Snippets
©"Robert"Brown"March"2015"@robby_brown

30. Resources(to(Learn(More
• Separa'on*of*Concerns
• Cohesion
• Orthogonality
©"Robert"Brown"March"2015"@robby_brown