How to detect scroll direction programmatically in SwiftUI ScrollView

问题

I want display or hide items by scroll direction just like safari. Hide something when scroll up, and show it when scroll down.

回答1:

You would use GeometryReader to get the global position of one in the views in the ScrollView to detect the scroll direction. The code below will print out the current midY position. Dependent on the +/- value you could display or hide other views.

struct ContentView: View {

var body: some View {
    ScrollView{
        GeometryReader { geometry in

                Text("Top View \(geometry.frame(in: .global).midY)")
                    .frame(width: geometry.size.width, height: 50)
                    .background(Color.orange)
            }

    }.frame(minWidth: 0, idealWidth: 0, maxWidth: .infinity, minHeight: 0, idealHeight: 0, maxHeight: .infinity, alignment: .center)
}

}

回答2:

You can use DragGesture value

ScrollView {
...
}
.gesture(
   DragGesture().onChanged { value in
      if value.translation.height > 0 {
         print("Scroll down")
      } else {
         print("Scroll up")
      }
   }
)

回答3:

I think, simultaneousGesture is a better solution because it's not blocking scrollView events.

ScrollView {

}
.simultaneousGesture(
       DragGesture().onChanged({
           let isScrollDown = 0 < $0.translation.height
           print(isScrollDown)
       }))

来源：https://stackoverflow.com/questions/59342384/how-to-detect-scroll-direction-programmatically-in-swiftui-scrollview