MVVM or Model - View - ViewModel is a design pattern aimed for modularising your code and build it on a Test Driven Development environment. When Apple's traditional MVC design pattern makes our controllers bulky and our unit tests painful, different design patterns such as MVVM, VIPER, MVP, etc come to our rescue. MVVM comes quite handy as it provides a loosely coupled mechanism between all components segregating your view, business and data logic.

1. G. ABHISEK
iOS Developer at Kuliza
MVVM and (UI +VM+
Data) Binding

2. Our Journey
• MVVM ?
• Why MVVM?
• Thumb rules of MVVM.
• Hiccups of MVVM.
• Some common data + UIBinding scenarios
• Communications
• View Code Reusability

3. MVVM ?
Model View Model View
or
View Controller
Owns Owns
Updates VM
via callbacks
Configures the data and
update
Updates VM of user actions
via callbacks

4. Why MVVM ?
Test Driven DevelopmentBuilds Segregated Code Avoids bulky controllers

5. Thumb Rules
of
MVVM
• View Model is responsible only for processing input to
output and logic required for driving the UI.
• View should be only responsible for UI handling.
• View should not interact with Data Model or vice-versa.
• View Model should not modify the UI.

6. Common HICCUPS while
Building MVVM
• Data Binding of complex UI components.
Eg. Data source of TableViews and CollectionViews with a broad number
of cell types.
• Communication between various MVVM components ->
Delegates, Closures, KVO ..… OOPS!!!
• UI logic is sometimes messed in Model and ViewModel.

7. UI + ViewModel + DataBinding

9. Table or Collection View with multiple cell types
Cell 1 (CellVM1)
Cell N (CellVM2)
.
.
.
.
.
.
.
VM
Cell Enums associated with Cell VM
- Holds the data
- Holds the cell state
- Updates the view
model
of User Actions
Owns

11. Communication
and
Binding

12. Closures
View
View
Model
Model
vm.eventHandler()
processCompleted(data: Any)
vm.update()
updateCompleted(data: Any)

13. 2 - Way Binding
• KVO
• RXSwift
• Reactive design pattern
https://codeburst.io/swift-mvvm-two-way-binding-win-b447edc55ff5

14. MVVM …..!!!
View Code Reusability

15. ViewModel 1
ViewModel
Representable
- Inputs to the VM
- Outputs to VM
- Any generic
methods
ViewModel 2
ViewModel 3
Confirm
View
VM Instance
Its a
VMRepresentableType!
Protocols to Rescue ..

16. Thank You !!