Allow to put dropdowns with dynamic width into the horizontal list

packages/dropdown_button2/lib/src/dropdown_button2.dart

@@ -802,23 +802,28 @@ class _DropdownButton2State<T> extends State<DropdownButton2<T>> with WidgetsBin
               // which enhances the performance when dealing with big items list.
               // Note: Both buttonHeight & buttonWidth must be specified to avoid changing
               // button's size when selecting different items, which is a bad UX.
-              return buttonHeight != null && _buttonStyle?.width != null
+              return buttonHeight != null
                   ? Align(
                       alignment: widget.alignment,
                       child: item,
                     )
-                  : IndexedStack(
-                      index: _selectedIndex ?? hintIndex,
-                      alignment: widget.alignment,
-                      children: buttonHeight != null
-                          ? buttonItems
-                          : buttonItems.map((item) {
-                              return Column(
-                                mainAxisSize: MainAxisSize.min,
-                                children: <Widget>[item],
-                              );
-                            }).toList(),
-                    );
+                  : _buttonStyle?.width != null
+                      ? IndexedStack(
+                          index: _selectedIndex ?? hintIndex,
+                          alignment: widget.alignment,
+                          children: buttonHeight != null
+                              ? buttonItems
+                              : buttonItems.map((item) {
+                                  return Column(
+                                    mainAxisSize: MainAxisSize.min,
+                                    children: <Widget>[item],
+                                  );
+                                }).toList(),
+                        )
+                      : SizedBox(
+                          height: buttonHeight,
+                          child: item,
+                        );
             },
           );
 
@@ -849,7 +854,10 @@ class _DropdownButton2State<T> extends State<DropdownButton2<T>> with WidgetsBin
                 mainAxisAlignment: MainAxisAlignment.spaceBetween,
                 mainAxisSize: MainAxisSize.min,
                 children: <Widget>[
-                  if (widget.isExpanded) Expanded(child: innerItemsWidget) else innerItemsWidget,
+                  if (widget.isExpanded && _buttonStyle?.width != null)
+                    Expanded(child: innerItemsWidget)
+                  else
+                    innerItemsWidget,
                   IconTheme(
                     data: IconThemeData(
                       color: _iconColor,

packages/dropdown_button2/lib/src/dropdown_route.dart

@@ -409,29 +409,29 @@ class _DropdownMenuRouteLayout<T> extends SingleChildLayoutDelegate {
       DropdownDirection.textDirection => switch (textDirection!) {
           TextDirection.rtl => clampDouble(
               buttonRect.right - childSize.width + offset.dx,
-              0.0,
-              size.width - childSize.width,
+              route.dropdownStyle.margin?.right ?? 0.00,
+              size.width - childSize.width - (route.dropdownStyle.margin?.left ?? 0),
             ),
           TextDirection.ltr => clampDouble(
               buttonRect.left + offset.dx,
-              0.0,
-              size.width - childSize.width,
+              route.dropdownStyle.margin?.left ?? 0.00,
+              size.width - childSize.width - (route.dropdownStyle.margin?.right ?? 0),
             ),
         },
       DropdownDirection.right => clampDouble(
           buttonRect.left + offset.dx,
-          0.0,
-          size.width - childSize.width,
+          route.dropdownStyle.margin?.right ?? 0.00,
+          size.width - childSize.width - (route.dropdownStyle.margin?.left ?? 0),
         ),
       DropdownDirection.left => clampDouble(
           buttonRect.right - childSize.width + offset.dx,
-          0.0,
-          size.width - childSize.width,
+          route.dropdownStyle.margin?.right ?? 0.00,
+          size.width - childSize.width - (route.dropdownStyle.margin?.right ?? 0),
         ),
       DropdownDirection.center => clampDouble(
           (size.width - childSize.width) / 2 + offset.dx,
-          0.0,
-          size.width - childSize.width,
+          route.dropdownStyle.margin?.left ?? 0.00,
+          size.width - childSize.width - (route.dropdownStyle.margin?.right ?? 0),
         ),
     };
 

packages/dropdown_button2/lib/src/dropdown_style_data.dart

@@ -4,6 +4,7 @@ part of 'dropdown_button2.dart';
 class DropdownStyleData {
   /// Creates a DropdownStyleData.
   const DropdownStyleData({
+    this.margin,
     this.maxHeight,
     this.width,
     this.padding,
@@ -21,6 +22,9 @@ class DropdownStyleData {
     this.dropdownBuilder,
   });
 
+  /// The outer margin of the dropdown menu
+  final EdgeInsets? margin;
+
   /// The maximum height of the dropdown menu
   ///
   /// The maximum height of the menu must be at least one row shorter than
@@ -112,6 +116,7 @@ class DropdownStyleData {
   /// Create a clone of the current [DropdownStyleData] but with the provided
   /// parameters overridden.
   DropdownStyleData copyWith({
+    EdgeInsets? margin,
     double? maxHeight,
     double? width,
     EdgeInsetsGeometry? padding,
@@ -129,6 +134,7 @@ class DropdownStyleData {
     DropdownBuilder? dropdownBuilder,
   }) {
     return DropdownStyleData(
+      margin: margin ?? this.margin,
       maxHeight: maxHeight ?? this.maxHeight,
       width: width ?? this.width,
       padding: padding ?? this.padding,