CS193p Notes - Lecture 8: Gestures JSON

#ios #swift

UserDefaults

Numerous ways to make data persists in iOS:
- FileManager filesystem
- CoreData SQL database
- CloudKit database in the cloud
- 3rd party options
- UserDefaults simplest to use but only for lightweight data. Like dictionary.
UserDefaults is most often used by making one instance and using it everywhere
- let defaults = UserDefaults.standard
defaults.set(object, forKey: "SomeKey")
- let i: Int = defaults.integer(forKey: "MyInteger")
- let b: Data? = defaults.data(forKey: "MyData")
- let a = array(forKey: "MyArray") this returnsArray<Any>
  - To useAny type it's possible to change the type withas

Gestures (8:37)

myView.gesture(theGesture)
gesture is implemented in func or computer var

vartheGesture:someGesture{returnTapGesture(count:2).onEnded{}}

non-discrete gestures

To see end result

vartheGesture:someGesture{DragGesture(...).onEnded{valuein...}}

To see the value of gesture

@GestureStatevarmyGestureState:MyGestureStateType=<startingvalue>

Returns<starting value> always when the gesture ends.

vartheGesture:someGesture{DragGesture(...).updating($myGestureState){value,myGestureState,transactioninmyGestureState=/* usually something related to value */}.onEnded{valuein/* do something */}}

myGestureState can be modified only inside.updating

vartheGesture:someGesture{DragGesture(...).onChanged{valuein/* do something with value (which is the state of the fingers) */.onEnded{valuein/* do something */}}

.updating is better in most of the cases because you care only the relative change

Demo (22:21)

UserDefaults.standard.set(emojiArt.json, forKey: "EmojiArtDocument.Untitled")
Codable property means that struct can be encoded and decoded

varjson:Data?{returntry?JSONEncoder().encode(self)}init?(json:Data?){ifjson!=nil,letnewEmojiArt=try?JSONDecoder().decode(EmojiArt.self,from:json!){self=newEmojiArt}else{returnnil}}

Double tap makes zooms in a way that you can see the full image

....gesture(self.doubleTapToZoom(in:geometry.size))...privatefuncdoubleTapToZoom(insize:CGSize)->someGesture{TapGesture(count:2).onEnded{withAnimation{self.zoomToFit(self.document.backgroundImage,in:size)}}}privatefunczoomToFit(_image:UIImage?,insize:CGSize){ifletimage=image,image.size.width>0,image.size.height>0{lethZoom=size.width/image.size.widthletvZoom=size.height/image.size.heightself.zoomScale=min(hZoom,vZoom)}}