[add] actionWillSelect

`tabItem(_:label:actionWillSelect:)` accepts a closure performing before the tab is selected.

Author: zijievv

Example/Example/ContentView.swift

@@ -19,33 +19,31 @@ struct ContentView: View {
 
     var body: some View {
         TabBar(selection: $item, visibility: $visibility) {
-            TextField("", text: $text)
-                .textFieldStyle(.roundedBorder)
-                .padding()
-                .background(.brown)
+            homeView()
                 .tabItem(0) {
                     Image(systemName: item == 0 ? "house.fill" : "house")
                         .font(.title3)
                     Text("Home")
                         .font(.system(.footnote, design: .rounded).weight(item == 0 ? .bold : .medium))
+                } actionWillSelect: {
+                    if item == 0 {
+                        text = ""
+                    }
                 }
-            List(1...30, id: \.self) { Text("Row \($0)") }
+            marksView()
                 .tabItem(1) {
                     Image(systemName: item == 1 ? "star.fill" : "star")
                         .font(.title3)
                     Text("Marks")
                         .font(.system(.footnote, design: .rounded).weight(item == 1 ? .bold : .medium))
                 }
-            ZStack {
-                Color.orange
-                Text("User View")
-            }
-            .tabItem(2) {
-                Image(systemName: item == 2 ? "person.fill" : "person")
-                    .font(.title3)
-                Text("User")
-                    .font(.system(.footnote, design: .rounded).weight(item == 2 ? .bold : .medium))
-            }
+            userView()
+                .tabItem(2) {
+                    Image(systemName: item == 2 ? "person.fill" : "person")
+                        .font(.title3)
+                    Text("User")
+                        .font(.system(.footnote, design: .rounded).weight(item == 2 ? .bold : .medium))
+                }
         }
         .tabBarFill(.regularMaterial)
         .tabBarForeground {
@@ -69,6 +67,26 @@ struct ContentView: View {
         }
     }
 
+    private func homeView() -> some View {
+        TextField("", text: $text)
+            .textFieldStyle(.roundedBorder)
+            .padding()
+            .background(.brown)
+    }
+
+    private func marksView() -> some View {
+        List(1...30, id: \.self) {
+            Text("Row \($0)")
+        }
+    }
+
+    private func userView() -> some View {
+        ZStack {
+            Color.orange
+            Text("User View")
+        }
+    }
+
     private func nextVisibility() {
         switch visibility {
         case .automatic: visibility = .visible

Sources/TabBarModule/Internal/PreferenceKey/ItemActionWillSelectPreferenceKey.swift

@@ -0,0 +1,37 @@
+//
+//  ItemActionWillSelectPreferenceKey.swift
+//
+//
+//  Created by Zijie V  on 24/08/2023.
+//  Copyright © 2023 Zijie V . All rights reserved.
+//
+//  ====================================================================================================================
+//
+
+import SwiftUI
+
+struct ItemActionWillSelectPreferenceKey<Selection: Hashable>: PreferenceKey {
+    static var defaultValue: [Selection: TabItemAction<Selection>] { [:] }
+
+    static func reduce(
+        value: inout [Selection: TabItemAction<Selection>],
+        nextValue: () -> [Selection: TabItemAction<Selection>]
+    ) {
+        value.merge(nextValue(), uniquingKeysWith: { $1 })
+    }
+}
+
+struct TabItemAction<Selection: Hashable>: Hashable, Equatable {
+    let selectedItemHashValue: Int?
+    let item: Selection
+    let action: ActionWillSelect?
+
+    func hash(into hasher: inout Hasher) {
+        hasher.combine(selectedItemHashValue)
+        hasher.combine(item)
+    }
+
+    static func == (lhs: TabItemAction, rhs: TabItemAction) -> Bool {
+        lhs.hashValue == rhs.hashValue
+    }
+}

Sources/TabBarModule/Internal/ViewModifier/TabItemViewModifier.swift

@@ -14,10 +14,12 @@ struct TabItemViewModifier<Selection: Hashable, V: View>: ViewModifier {
     @Environment(\.tabItemSelectionHashValue) private var selectionHashValue
     private let item: Selection
     @ViewBuilder private let itemBuilder: () -> V
+    private let actionWillSelect: ActionWillSelect?
 
-    init(item: Selection, @ViewBuilder itemBuilder: @escaping () -> V) {
+    init(item: Selection, @ViewBuilder itemBuilder: @escaping () -> V, actionWillSelect: ActionWillSelect?) {
         self.item = item
         self.itemBuilder = itemBuilder
+        self.actionWillSelect = actionWillSelect
     }
 
     func body(content: Content) -> some View {
@@ -35,5 +37,11 @@ struct TabItemViewModifier<Selection: Hashable, V: View>: ViewModifier {
                     )
                 ]
             )
+            .preference(
+                key: ItemActionWillSelectPreferenceKey.self,
+                value: [
+                    item: TabItemAction(selectedItemHashValue: selectionHashValue, item: item, action: actionWillSelect)
+                ]
+            )
     }
 }

Sources/TabBarModule/Public/TabBar.swift

@@ -24,6 +24,7 @@ public struct TabBar<Selection, Content>: View where Selection: Hashable, Conten
     @Environment(\.tabBarShape) private var barShape
     @State private var items: [Selection] = []
     @State private var tabItemBuilders: [Selection: AnyItemViewBuilder<Selection>] = [:]
+    @State private var tabItemActions: [Selection: TabItemAction<Selection>] = [:]
     @Binding private var selection: Selection
     @Binding private var visibility: Visibility
     @StateObject private var keyboardObserver: KeyboardObserver = .shared
@@ -46,6 +47,7 @@ public struct TabBar<Selection, Content>: View where Selection: Hashable, Conten
                 .safeAreaInset(edge: .bottom, alignment: .center, spacing: barSpacing) { tabBar(in: geo) }
                 .onPreferenceChange(ItemsPreferenceKey<Selection>.self) { self.items = $0 }
                 .onPreferenceChange(ItemViewBuilderPreferenceKey<Selection>.self) { self.tabItemBuilders = $0 }
+                .onPreferenceChange(ItemActionWillSelectPreferenceKey<Selection>.self) { self.tabItemActions = $0 }
                 .environment(\.tabItemSelectionHashValue, selection.hashValue)
                 .animation(animationBuilder(isVisible), value: isVisible)
         }
@@ -71,7 +73,10 @@ public struct TabBar<Selection, Content>: View where Selection: Hashable, Conten
         if let builder = tabItemBuilders[item]?.content {
             builder()
                 .contentShape(Rectangle())
-                .onTapGesture { selection = item }
+                .onTapGesture {
+                    tabItemActions[item]?.action?()
+                    selection = item
+                }
                 .frame(width: width)
         }
     }

Sources/TabBarModule/Public/View+Extension.swift

@@ -10,17 +10,19 @@
 
 import SwiftUI
 
+public typealias ActionWillSelect = () -> Void
+
 extension View {
     public func tabItem<Selection: Hashable, V: View>(
         _ selection: Selection,
-        @ViewBuilder label: @escaping () -> V
+        @ViewBuilder label: @escaping () -> V,
+        actionWillSelect: ActionWillSelect? = nil
     ) -> some View {
-        modifier(TabItemViewModifier(item: selection, itemBuilder: label))
+        modifier(TabItemViewModifier(item: selection, itemBuilder: label, actionWillSelect: actionWillSelect))
     }
 
     public func tabBarFill<S: ShapeStyle>(_ content: S, style: FillStyle = .init()) -> some View {
-        self
-            .environment(\.tabBarShapeStyle, .init(AnyShapeStyle(content)))
+        self.environment(\.tabBarShapeStyle, .init(AnyShapeStyle(content)))
             .environment(\.tabBarFillStyle, style)
     }