Cbowdoin/bottom sheet supports x axis constraints (microsoft#1951)

* Add in the ability specify preferredWidth can control contraints

* Cleaned up anchor description and simplified logic

* Cleaned up whitespace and paranthesis

* Fixed bug for leading and trailing edge not support rtl languanges. Also fixed minor formatting issuees

* fixed up minor formatting issues

* Adding padding to the bottom sheet constants

* Changed anchoredEdge logic to use a switch

* Replaced magic number with global spacing token

* Avoided setting public properties internally

* Swapped sheet width logic from using a closure to use a method

* Fixed naming on anchored edge objective-c consumption and removed early return

ios/FluentUI.Demo/FluentUI.Demo/Demos/BottomSheetDemoController.swift

@@ -91,6 +91,14 @@ class BottomSheetDemoController: DemoController {
         bottomSheetViewController?.preferredExpandedContentHeight = sender.isOn ? 0 : 400
     }
 
+    @objc private func toggleTrailingEdge(_ sender: BooleanCell) {
+        bottomSheetViewController?.anchoredEdge = sender.isOn ? .trailing : .center
+    }
+
+    @objc private func togglePreferredWidth(_ sender: BooleanCell) {
+        bottomSheetViewController?.preferredWidth = sender.isOn ? 400 : 0
+    }
+
     @objc private func showTransientSheet() {
         let hostingVC = UIHostingController(rootView: BottomSheetDemoListContentView())
 
@@ -249,7 +257,15 @@ class BottomSheetDemoController: DemoController {
                 DemoItem(title: "Hide collapsed content", type: .boolean, action: #selector(toggleCollapsedContentHiding), isOn: collapsedContentHidingEnabled),
                 DemoItem(title: "Flexible sheet height", type: .boolean, action: #selector(toggleFlexibleSheetHeight), isOn: bottomSheetViewController?.isFlexibleHeight ?? false),
                 DemoItem(title: "Use custom handle accessibility label", type: .boolean, action: #selector(toggleHandleUsingCustomAccessibilityLabel), isOn: isHandleUsingCustomAccessibilityLabel),
-                DemoItem(title: "Full screen sheet content", type: .boolean, action: #selector(toggleFullScreenSheetContent), isOn: bottomSheetViewController?.preferredExpandedContentHeight == 0)
+                DemoItem(title: "Full screen sheet content", type: .boolean, action: #selector(toggleFullScreenSheetContent), isOn: bottomSheetViewController?.preferredExpandedContentHeight == 0),
+                DemoItem(title: "Attach to trailing edge",
+                          type: .boolean,
+                        action: #selector(toggleTrailingEdge),
+                          isOn: bottomSheetViewController?.anchoredEdge == .trailing),
+                DemoItem(title: "Set preferred width to 400",
+                          type: .boolean,
+                        action: #selector(togglePreferredWidth),
+                          isOn: bottomSheetViewController?.preferredWidth == 400)
             ],
             [
                 DemoItem(title: "Show transient sheet", type: .action, action: #selector(showTransientSheet))

ios/FluentUI/Bottom Sheet/BottomSheetController.swift

@@ -39,6 +39,13 @@ public protocol BottomSheetControllerDelegate: AnyObject {
     case transitioning // Sheet is between states, only used during user interaction / animation
 }
 
+/// Defines where the sheet should be postionioned relative to the screen space
+@objc(MSFBottomSheetAnchorEdge) public enum BottomSheetAnchorEdge: Int {
+    case center // Sheet is centered on the screen
+    case leading // Sheet is constrained to the leading edge
+    case trailing // Sheet is constrained to the trailing edge
+}
+
 @objc(MSFBottomSheetController)
 public class BottomSheetController: UIViewController, Shadowable, TokenizedControlInternal {
 
@@ -223,6 +230,28 @@ public class BottomSheetController: UIViewController, Shadowable, TokenizedContr
         }
     }
 
+    /// Setting this property  will result in the sheet trying to be as close to this width as possible.
+    /// If the declared width is too large it will roll back to the maximum width
+    @objc open var preferredWidth: CGFloat = 0 {
+        didSet {
+            let shouldInvalidateLayout = (preferredWidth != oldValue) && isViewLoaded
+            if shouldInvalidateLayout {
+                view.setNeedsLayout()
+            }
+        }
+    }
+
+    /// Represents where the sheet should appear on the screen. 
+    /// Defaults to being centered
+    @objc open var anchoredEdge: BottomSheetAnchorEdge = .center {
+        didSet {
+            guard anchoredEdge != oldValue && isViewLoaded else {
+                return
+            }
+            view.setNeedsLayout()
+        }
+    }
+
     /// When enabled, users will be able to move the sheet to the hidden state by swiping down.
     @objc open var allowsSwipeToHide: Bool = false
 
@@ -721,8 +750,8 @@ public class BottomSheetController: UIViewController, Shadowable, TokenizedContr
     // Source of truth for the sheet frame at a given offset from the top of the root view bounds.
     // The output is only meaningful once view.bounds is non-zero i.e. a layout pass has occured.
     private func sheetFrame(offset: CGFloat) -> CGRect {
-        let availableWidth: CGFloat = view.bounds.width
-        let sheetWidth = shouldAlwaysFillWidth ? availableWidth : min(Constants.maxSheetWidth, availableWidth)
+        let sheetWidth: CGFloat = determineSheetWidth()
+
         let sheetHeight: CGFloat
 
         if isFlexibleHeight {
@@ -732,8 +761,50 @@ public class BottomSheetController: UIViewController, Shadowable, TokenizedContr
             sheetHeight = expandedSheetHeight
         }
 
-        return CGRect(origin: CGPoint(x: (view.bounds.width - sheetWidth) / 2, y: offset),
-                      size: CGSize(width: sheetWidth, height: sheetHeight))
+        // Calculates the location to put the left edge of the sheet relative to the view
+        // For right aligned we get the width of the view offset by the sheets width and the padding
+        // For left aligned we only need to add in the padding
+        // For center aligned we need the position of the center offset by half the sheets width
+        let xPosition: CGFloat
+        let isLeftToRight: Bool = UIView.userInterfaceLayoutDirection(for: view.semanticContentAttribute) == .leftToRight
+        switch anchoredEdge {
+        case .center:
+            xPosition = (view.bounds.width - sheetWidth) / 2
+        case .leading:
+            if isLeftToRight {
+                xPosition = Constants.horizontalSheetPadding
+            } else {
+                xPosition = view.bounds.width - sheetWidth - Constants.horizontalSheetPadding
+            }
+        case .trailing:
+            if isLeftToRight {
+                xPosition = view.bounds.width - sheetWidth - Constants.horizontalSheetPadding
+            } else {
+                xPosition = Constants.horizontalSheetPadding
+            }
+        }
+
+        let frame = CGRect(origin: CGPoint(x: xPosition, y: offset),
+                             size: CGSize(width: sheetWidth, height: sheetHeight))
+        return frame
+    }
+
+    // Helper function to determine how wide the sheet should be
+    private func determineSheetWidth() -> CGFloat {
+        // Width will the fill the screen if should always fill width
+        // Otherwise we will try and set the size to the preferred width as long as its between the max and min width
+        // If its not between those we will make the maximum width size
+        let availableWidth: CGFloat = view.bounds.width
+        let maxWidth = min(Constants.maxSheetWidth, availableWidth)
+        let determinedWidth: CGFloat
+        if shouldAlwaysFillWidth {
+            determinedWidth = availableWidth
+        } else if Constants.minSheetWidth...maxWidth ~= preferredWidth {
+            determinedWidth = preferredWidth
+        } else {
+            determinedWidth = maxWidth
+        }
+        return determinedWidth
     }
 
     private func translationRubberBandFactor(for currentOffset: CGFloat) -> CGFloat {
@@ -1064,6 +1135,9 @@ public class BottomSheetController: UIViewController, Shadowable, TokenizedContr
         // Minimum padding from top when the sheet is fully expanded
         static let minimumTopExpandedPadding: CGFloat = 25.0
 
+        // The padding allocated to the space between the sheet and the edge when attached to the leading or trailing edge
+        static let horizontalSheetPadding: CGFloat = GlobalTokens.spacing(.size80)
+
         static let expandedContentAlphaTransitionLength: CGFloat = 30
 
         static let maxSheetWidth: CGFloat = 610