# 13, 14

- 13: Publisher, CloudKit, CoreData
- 14: App Architecture, Document Architecture, Undo

## Publisher


// fetch the url
backgroundImageFetchStatus = .fetching

DispatchQueue.global(qos: .userInitiated).async {
    let imageData = try? Data(contentsOf: url)
    DispatchQueue.main.async { [weak self] in
        if self?.emojiArt.background == EmojiArtModel.Background.url(url) {
            self?.backgroundImageFetchStatus = .idle
            if imageData != nil {
                self?.backgroundImage = UIImage(data: imageData!)
            }
        }
    }
}

// fetch the url
backgroundImageFetchStatus = .fetching

let session = URLSession.shared
let publisher = session.dataTaskPublisher(for: url)
    .map { (data, urlResponse) in UIImage(data: data) }
    .replaceError(with: nil)
    .receive(on: DispatchQueue.main)

backgroundImageFetchCancellable = publisher
    .sink { [weak self] image in
        self?.backgroundImage = image
        self?.backgroundImageFetchStatus = image != nil ? .idle : .failed(url)
    }

1. 取得 Publisher (subscription)
2. Publisher 設定
- `.map(_:)` 改變產物
- `.receive(on: DispatchQueue.main)`
3. Publisher 資料接收
- `.sink(receiveValue:)` 處理產出的資料
4. Cancellable 保存與使用

> Publisher 有很多 method 很像 array 的 method，`.map(_:)`

- URLSession
- Timer
- NotificationCenter

## CoreData

- @ObservedObject
- @FetchRequest

## App Architecture

- `App` protocol
- `Scene` protocol
- WindowGroup { }
- DocumentGroup(newDocument:) { }
- DocumentGroup(viewing:) { }
- `@SenceStorage`
- `@AppStorage`
- `@ScaledMetric`


@SceneStorage("EmojiArtDocument.steadyStatePanOffset")
var steadyStatePanOffset: CGSize = .zero

@SceneStorage("EmojiArtDocumentView.steadyStateZoomScale")
var steadyStateZoomScale: CGFloat = 1

@AppStorage("username") 
var username: String = "Anonymous"

- 被存在 `UserDefaults.standard`
- 所以不推薦存大量資料
- 所以不要存機敏性資料

7:48 Code

app icon -> Asset.xcassets

19:56 `RawRepresentable`

每次開啟 app 後 load backgroundImage 完成又去 zoomToFit

## 28:02 Document Architecture

* FileDocument
* ReferenceFileDocument
* UTType
* Document Types
* 39:05 Undo

func undoablyPerform(operation: String, with undoManager: UndoManager?) {
    let oldModel = model
    doIt()
    undoManager?.registerUndo(withTarget: self) { mySelf in
        mySelf.model = oldModel
    }
    undoManager?.setActionName(operation)
}

## 43:14 Back To Code

- 49:50 讓 **ViewModel** conform to `ReferenceFileDocument`
- 1:02:16 undo imple
- 1:12:01 support document

https://github.com/skkimeo/CS193p-Spring-2021