On one of the more mediocre episodes of Fireside Swift , McSwiftface and Zach talk about the SOLID principles of class design, although I don’t hold the principles as the article of religious fervour that many interviewers apparently do, they are a useful touchstone for considering class quality. OOP had been in swing (in a commercial way) for a few years by then - I was writing in Delphi and C++. The spaghetti code era was a long way behind us and the idea of separation of responsibilities was well established.
The Youtube algorithm thinks I need to watch more MVVM videos, and it turns out it’s probably right. A day or two ago in an MVVM post using a super simple example, I stored the view model as a property of the view using the @ObservedObject wrapper, as I created it.
struct ContentView: View {
@ObservedObject var light = LightViewModel()
var body: some View {
VStack{
Spacer()
if light.isOn(){
drawLitBulb
}
else{
Image(systemName: "lightbulb.fill").font(.system(size: 72))
}
MVVM (Model-View-View Model) is an architectural pattern for apps that separates the data (Model) from the user interface (View). The communication between these two parts is facilitated by a View Model.
Model <-> View Model <-> View
Model
The Model is platform independent - we should be able to pluck it out and add it to a different application running on a different platform without any trouble. Any business rules will be part of the Model along with the data. For example, if it’s a rule that every customer has a sales contact, this can be enforced in the Model.
The first nine minutes of this video from Emmanuel Okwara finally gave me a clear understanding of the difference between MVC and MVVM.
In both MVC and MVVM the data & logic (Model) are separated from the part that the user interacts (View). Usually the View is a screen with controls and so on, but that’s not compulsory - for example a voice mail app interface would be all audio and DTMF. The point is that in both, the user interface (view) does not mess directly with the data (model) - it has to go through some sort of gatekeeper.
