How to build custom TabBar using SwiftUI?

Xode 12 — iOS 14

Demo -Image

Implementation Logic

• Build Bottom Bar HStack UI with tab Item
• Move/Translate selected tab up on Tap
• Draw Bar path as curve around selected Indes

First we create a tab Item object which contains Tab Icon name and the relative offset.

class TabItem: Identifiable {
    let id = UUID()
    let imageName: String
    var offset: CGFloat = -5
    var opacity: Double = 1
    
    init(imageName: String, offset: CGFloat) {
        self.imageName = imageName
        self.offset = offset
    }
    init(imageName: String) {
        self.imageName = imageName
    }
}

Create a ObservableObject to help update selected index.

class TabItems: ObservableObject {
    @Published var items: [TabItem] = [
        TabItem(imageName: "house", offset: -20),
        TabItem(imageName: "magnifyingglass"),
        TabItem(imageName: "plus.app"),
        TabItem(imageName: "heart"),
        TabItem(imageName: "person"),
    ]
    @Published var selectedTabIndex: CGFloat = 1
    func select(_ index: Int) {
        let tabItem = items[index]
        
        tabItem.opacity = 0
        tabItem.offset = 15
        
        withAnimation(Animation.easeInOut) {
            selectedTabIndex = CGFloat(index + 1)
            for i in 0..<items.count {
                if i != index {
                    items[i].offset = -5
                }
            }
        }
        withAnimation(Animation.easeOut(duration: 0.25).delay(0.25)) {
            tabItem.opacity = 1
            tabItem.offset = -25
        }
    }
}

Now, Create HStack with in VStack with Spacer on top to move the view below.

Also, We calculate the position of every tab Item to create curve on select.

Using firstCenter and stepperToNextCenter, we create a curve to the selected index

Complete Code: