🔰update gesture states

SwiftUI ⟩ Gestures ⟩ update gesture states

Gesture state is "transient" which means it will reset back to its initial state when user ends or cancels the gesture.

To update a view as a gesture changes, add a GestureState property to your view and update it with updating(_:body:).
SwiftUI invokes the updating callback as soon as it recognizes the gesture and whenever the value of the gesture changes.
SwiftUI doesn’t invoke the updating callback when the user ends or cancels a gesture. Instead, the gesture state property automatically resets its state back to its initial value.

// ⭐️ updates @GestureState var as the gesture’s value changes.
//    `updating($state){ value, state, transaction in ... }`
func updating<State>(
    _ state: GestureState<State>, 
    body: @escaping (
        Self.Value,         // gesture's current value
        inout State,        // @GestureState var to be updated
        inout Transaction   // animation "context" (❓)
    ) -> Void
) -> GestureStateGesture<Self, State>

⬆️ 需要： TimerView

struct ContentView: View {
    
    // ⭐️ gesture state:
    //    reset to initial value when ends or cancels.
    @GestureState var isPressing = false
    
    var body: some View {
        
        // long press (for 3 sec)
        let press = LongPressGesture(minimumDuration: 3)
            // ⭐️ update gesture state
            .updating($isPressing) { value, state, _ in
                state = value
            }
        
        return Circle()
            .fill(isPressing ? .pink : .green)
            .frame(width: 100, height: 100, alignment: .center)
            .gesture(press)    // ⭐️ apply gesture
            .overlay {
                if isPressing {
                    // 👔 TimeView: count-down timer
                    TimerView(seconds: 3) { sec in
                        Text("\(sec)").font(.system(size: 50)).bold()
                    }   
                }
            }
    }
}

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Last updated 3 years ago