# CS193P - Lecture 9: EmojiArt Drag and Drop Multithreading

- 5:35 `RangeReplaceableCollection`
- 因為 `Collection` 是 immutable，所以改成 `RangeReplaceableCollection`
- 6:16 subscripting
- `cards[card].isFaceUp = true`
- If no card with the `card.id` exists in cards, then this does nothing.
- 8:51 `Color` / `UIColor` / `CGColor`
- 13:00 `Image` / `UIImage`
- 15:42 Drag and Drop
- `NSItemProvider`
- facilitates the transfer of data between two processes

## 18:43 Demo

- MVVM
- fileprivate
- enum with associated values
- drag and drop