[FluentNotification] Add Expand button behavior

Demos/FluentUIDemo_iOS/FluentUI.Demo/Demos/NotificationViewDemoController_SwiftUI.swift

@@ -56,6 +56,7 @@ struct NotificationDemoView: View {
     @State var previewPresented: Bool = true
     @State var notificationID: UUID = UUID()
     @State var autoReappear: Bool = true
+    @State var expandButtonMode: Int = 0
     @ObservedObject var fluentTheme: FluentTheme = .shared
     private var triggerModel = FluentNotificationTriggerModel()
     let customTheme: FluentTheme = {
@@ -178,6 +179,7 @@ struct NotificationDemoView: View {
                                            message: hasMessage ? message : nil,
                                            attributedMessage: hasAttribute && hasMessage ? attributedMessage : nil,
                                            messageLineLimit: messageLineLimit,
+                                           enableExandableMessageText: expandButtonMode == 1,
                                            title: hasTitle ? title : nil,
                                            attributedTitle: hasAttribute && hasTitle ? attributedTitle : nil,
                                            image: image,
@@ -188,6 +190,8 @@ struct NotificationDemoView: View {
                                            showDefaultDismissActionButton: showDefaultDismissActionButton,
                                            showActionButtonAndDismissButton: showActionButtonAndDismissButton,
                                            defaultDismissButtonAction: dismissButtonAction,
+                                           showExpandButtonInPlaceOfDismissButton: expandButtonMode == 2,
+                                           expandButtonAction: (expandButtonMode == 2) ? { showAlert = true } : nil,
                                            messageButtonAction: messageButtonAction,
                                            swipeToDismissEnabled: swipeToDismissEnabled,
                                            showFromBottom: showFromBottom,
@@ -234,6 +238,7 @@ struct NotificationDemoView: View {
                                message: hasMessage ? message : nil,
                                attributedMessage: hasAttribute && hasMessage ? attributedMessage : nil,
                                messageLineLimit: messageLineLimit,
+                               enableExandableMessageText: expandButtonMode == 1,
                                isPresented: $isPresented,
                                title: hasTitle ? title : nil,
                                attributedTitle: hasAttribute && hasTitle ? attributedTitle : nil,
@@ -244,6 +249,8 @@ struct NotificationDemoView: View {
                                actionButtonAction: actionButtonAction,
                                showDefaultDismissActionButton: showDefaultDismissActionButton,
                                showActionButtonAndDismissButton: showActionButtonAndDismissButton,
+                               showExpandButtonInPlaceOfDismissButton: expandButtonMode == 2,
+                               expandButtonAction: (expandButtonMode == 2) ? { showAlert = true } : nil,
                                messageButtonAction: messageButtonAction,
                                showFromBottom: showFromBottom,
                                verticalOffset: verticalOffset,
@@ -280,6 +287,7 @@ struct NotificationDemoView: View {
                 LabeledContent {
                     TextField("Line Limit", value: $messageLineLimit, formatter: integerFormatter)
                         .keyboardType(.numberPad)
+                        .multilineTextAlignment(.trailing)
                 } label: {
                     Text("Message Line Limit")
                 }
@@ -316,6 +324,12 @@ struct NotificationDemoView: View {
                 Toggle("Can Show Action & Dismiss Buttons", isOn: $showActionButtonAndDismissButton)
                 Toggle("Has Message Action", isOn: $hasMessageAction)
                 Toggle("Swipe to Dismiss Enabled", isOn: $swipeToDismissEnabled)
+                Picker(selection: $expandButtonMode, label: Text("Expand Button Mode")) {
+                    Text("none").tag(0)
+                    Text("expandable message").tag(1)
+                    Text("custom expand action").tag(2)
+                }
+                .frame(maxWidth: .infinity, alignment: .leading)
             }
 
             FluentListSection("Style") {

Sources/FluentUI_iOS/Components/ExpandableText/ExpandableText.swift

@@ -0,0 +1,140 @@
+//
+//  Copyright (c) Microsoft Corporation. All rights reserved.
+//  Licensed under the MIT License.
+//
+
+import SwiftUI
+
+/// A text view that automatically detects truncation and supports expand/collapse functionality.
+///
+/// This component measures the rendered text height and determines if truncation is occurring
+/// based on the specified line limit. It provides an optional callback when expandability changes,
+/// allowing parent components to react (e.g., show/hide an expand button).
+///
+public struct ExpandableText: View {
+    // MARK: - Public Initializers
+
+    /// Creates an expandable text view with plain text.
+    /// - Parameters:
+    ///   - text: The text to display.
+    ///   - lineLimit: Maximum number of lines to show when collapsed. Default is 2.
+    ///   - isExpanded: Optional binding to control expansion state externally.
+    ///   - font: The font to use for measurement and display. If nil, uses system body font.
+    ///   - onExpandabilityChange: Callback invoked when the expandability status changes.
+    public init(
+        _ text: String,
+        lineLimit: Int = 0,
+        isExpanded: Binding<Bool>? = nil,
+        font: UIFont? = nil,
+        onExpandabilityChange: ((Bool) -> Void)? = nil
+    ) {
+        self.text = text
+        self.attributedText = nil
+        self.lineLimit = lineLimit
+        self.externalIsExpanded = isExpanded
+        self.font = font
+        self.onExpandabilityChange = onExpandabilityChange
+    }
+
+    /// Creates an expandable text view with attributed text.
+    /// - Parameters:
+    ///   - attributedText: The attributed text to display.
+    ///   - lineLimit: Maximum number of lines to show when collapsed. Default is 2.
+    ///   - isExpanded: Optional binding to control expansion state externally.
+    ///   - onExpandabilityChange: Callback invoked when the expandability status changes.
+    public init(
+        _ attributedText: NSAttributedString,
+        lineLimit: Int = 0,
+        isExpanded: Binding<Bool>? = nil,
+        onExpandabilityChange: ((Bool) -> Void)? = nil
+    ) {
+        self.text = attributedText.string
+        self.attributedText = attributedText
+        self.lineLimit = lineLimit
+        self.externalIsExpanded = isExpanded
+		self.font = attributedText.attribute(.font, at: 0, effectiveRange: nil) as? UIFont
+        self.onExpandabilityChange = onExpandabilityChange
+    }
+
+    // MARK: - Public Properties
+
+    public var body: some View {
+        Group {
+            if let attributed = attributedText {
+                Text(AttributedString(attributed))
+            } else {
+                Text(text)
+                    .font(font.map { Font($0) } ?? .body)
+            }
+        }
+        .lineLimit(isExpanded ? nil : (lineLimit > 0 ? lineLimit : nil))
+        .fixedSize(horizontal: false, vertical: true)
+        .onGeometryChange(for: CGFloat.self) { geo in
+            geo.size.width
+        } action: { width in
+            calculateTruncation(availableWidth: width)
+        }
+    }
+
+    // MARK: - Private Properties
+
+    private let text: String
+    private let attributedText: NSAttributedString?
+    private let lineLimit: Int
+    private let font: UIFont?
+    private let onExpandabilityChange: ((Bool) -> Void)?
+
+    @State private var isExpandable: Bool = false
+    @State private var internalIsExpanded: Bool = false
+    @State private var availableWidth: CGFloat = 0
+
+    private var externalIsExpanded: Binding<Bool>?
+
+    /// The current expansion state, reading from external binding if provided, otherwise using internal state.
+    private var isExpanded: Bool {
+        get { externalIsExpanded?.wrappedValue ?? internalIsExpanded }
+        nonmutating set {
+            if let binding = externalIsExpanded {
+                binding.wrappedValue = newValue
+            } else {
+                internalIsExpanded = newValue
+            }
+        }
+    }
+
+    /// The font to use for rendering and measurements, with fallback to body style.
+    private var effectiveFont: UIFont {
+        font ?? UIFont.preferredFont(forTextStyle: .body)
+    }
+
+    /// The height of a single line of text using the effective font.
+    private var singleLineHeight: CGFloat {
+        ceil(effectiveFont.lineHeight + max(0, effectiveFont.leading))
+    }
+
+    // MARK: - Private Methods
+
+    /// Calculates whether the text would be truncated by comparing the full text height to the maximum allowed height.
+    /// - Parameter availableWidth: The available width for rendering the text.
+    private func calculateTruncation(availableWidth: CGFloat) {
+        guard availableWidth > 0 else { return }
+
+        let messageText: String
+        if let attributedText {
+            messageText = attributedText.string
+        } else {
+            messageText = text
+        }
+        // Calculate the full height the text would take without line limit
+        let fullHeight = messageText.preferredSize(
+            for: effectiveFont,
+            width: availableWidth,
+            numberOfLines: 0
+        ).height
+        let maxHeight = singleLineHeight * CGFloat(lineLimit < 1 ? Int.max : lineLimit)
+
+        let newExpandable = fullHeight > maxHeight
+        isExpandable = newExpandable
+        onExpandabilityChange?(newExpandable)
+    }
+}