How should a UIView access the data model to display the data (using Swift)? - ios

Question

This seems like it should have a simple answer, and probably does, but it's proving harder to find than I expected. As a specific example, let's say that I'm programming a chess game.
It seems like this is something I should be able to do just using CoreGraphics. It seems like using OpenGL or SpriteKit shouldn't be necessary.
I want to have a Board class that models the state of the board. Where should I declare my Board object? My impression is that it should be in the ViewController.
I want to have a view (actually a subview) that displays the current state of the board (by overloading drawRect). It should do this at the beginning, and should be updated when players make moves. How does the view access the data model to display the board state? Does giving the view a reference to the data violate MVC? If not, how would the reference be passed to the view? (I seem to just find lots of links about passing data between two ViewControllers.)
Should it instead be the ViewController "pushing" the data to the view whenever it needs to be drawn? My understanding, though, is that drawRect should not be called directly, and that instead setNeedsDisplay should be called, which will indirectly result in drawRect being called. This being the case, it's hard to see how the data would be passed.

Answer 1

Your code; your design decision. Nothing to comment on here.
You should have your model declaration in ViewController. True. That is how MVC works.
Having a reference of the data in a UIView DOES break MVC. Your view instance will not be independent anymore. Decoupling view and model is one of the main points of MVC and you are probably breaking it with this design.
What can you do about it?
Extending #Paulw11's comment, in your view controller you can declare a method that looks something like this :
func movePiece(somePiece : Piece, toSquare : Square) {
let pieceID = somePiece.id //I am just assuming the models structures
let pieceImageView = self.pieceImageViewFromID(id) //Assume that this method returns the reference of the image view. Assume that I am just working UIKit here.
let fromPoint : CGPoint = somePiece.origin
let toPoint : CGPoint = toSquare.coordinates
self.animateView(pieceImageView, fromPoint:fromPoint, toPoint:toPoint)
}
Note that in this design, the view is not holding any model references; the view controller will take care of setting its state and bring upon relevant animations.
If you are overriding drawRect:, then yes, for it be called, you should call setNeedsDisplay to update the changes. The view controller might call or you can add property observers to redraw itself based on a property change. One example for this could be:
class SillyView : UIView {
var drawPonies : Bool = false {
didSet {
if oldValue != drawPonies {
self.setNeedsDisplay()
}
}
}
override func drawRect(rect: CGRect) {
if drawPonies {
self.drawGoodLookingPony()
} else {
self.drawSomeOtherAnimal()
}
}
func drawGoodLookingPony() {
//Draw a good looking pony here
}
func drawSomeOtherAnimal() {
//Draw Something else
}
}
If your view controller decides to draw ponies all you have to do is, get the reference of the SillyView and set drawPonies to true.
self.sillyView.drawPonies = true
You are not passing your data model here, but important pieces of configuration information that will help the view redraw itself.