Avoid Container objects when possible for better performance [Flutter…

packages/dropdown_button2/CHANGELOG.md

@@ -6,6 +6,7 @@
 - Form fields onChange callback should be called on reset [Flutter core].
 - Implement switch expressions.
 - Fix memory leak in CurvedAnimation [Flutter core].
+- Avoid Container objects when possible for better performance [Flutter core].
 
 ## 3.0.0-beta.21
 

packages/dropdown_button2/lib/src/dropdown_button2.dart

@@ -785,7 +785,7 @@ class _DropdownButton2State<T> extends State<DropdownButton2<T>>
           ? _textStyle!
           : _textStyle!.copyWith(color: Theme.of(context).disabledColor),
       child: widget.customButton ??
-          Container(
+          _ConditionalDecoratedBox(
             decoration: _buttonStyle?.decoration?.copyWith(
               boxShadow: _buttonStyle!.decoration!.boxShadow ??
                   kElevationToShadow[_buttonStyle!.elevation ?? 0],
@@ -794,45 +794,47 @@ class _DropdownButton2State<T> extends State<DropdownButton2<T>>
               boxShadow: _buttonStyle!.foregroundDecoration!.boxShadow ??
                   kElevationToShadow[_buttonStyle!.elevation ?? 0],
             ),
-            padding: (_buttonStyle?.padding ??
-                    padding.resolve(Directionality.of(context)))
-                .add(
-              // When buttonWidth & dropdownWidth is null, their width will be calculated
-              // from the maximum width of menu items or the hint text (width of IndexedStack).
-              // We need to add MenuHorizontalPadding so menu width adapts to max items width with padding properly
-              _buttonStyle?.width == null && _dropdownStyle.width == null
-                  ? _getMenuPadding()
-                      .resolve(Directionality.of(context))
-                      .copyWith(top: 0, bottom: 0)
-                  : EdgeInsets.zero,
-            ),
             height: buttonHeight,
             width: _buttonStyle?.width,
-            child: Row(
-              mainAxisAlignment: MainAxisAlignment.spaceBetween,
-              mainAxisSize: MainAxisSize.min,
-              children: <Widget>[
-                if (widget.isExpanded)
-                  Expanded(child: innerItemsWidget)
-                else
-                  innerItemsWidget,
-                IconTheme(
-                  data: IconThemeData(
-                    color: _iconColor,
-                    size: _iconStyle.iconSize,
-                  ),
-                  child: ValueListenableBuilder<bool>(
-                    valueListenable: _isMenuOpen,
-                    builder: (BuildContext context, bool isOpen, _) {
-                      return _iconStyle.openMenuIcon != null
-                          ? isOpen
-                              ? _iconStyle.openMenuIcon!
-                              : _iconStyle.icon
-                          : _iconStyle.icon;
-                    },
+            child: Padding(
+              padding: (_buttonStyle?.padding ??
+                      padding.resolve(Directionality.of(context)))
+                  .add(
+                // When buttonWidth & dropdownWidth is null, their width will be calculated
+                // from the maximum width of menu items or the hint text (width of IndexedStack).
+                // We need to add MenuHorizontalPadding so menu width adapts to max items width with padding properly
+                _buttonStyle?.width == null && _dropdownStyle.width == null
+                    ? _getMenuPadding()
+                        .resolve(Directionality.of(context))
+                        .copyWith(top: 0, bottom: 0)
+                    : EdgeInsets.zero,
+              ),
+              child: Row(
+                mainAxisAlignment: MainAxisAlignment.spaceBetween,
+                mainAxisSize: MainAxisSize.min,
+                children: <Widget>[
+                  if (widget.isExpanded)
+                    Expanded(child: innerItemsWidget)
+                  else
+                    innerItemsWidget,
+                  IconTheme(
+                    data: IconThemeData(
+                      color: _iconColor,
+                      size: _iconStyle.iconSize,
+                    ),
+                    child: ValueListenableBuilder<bool>(
+                      valueListenable: _isMenuOpen,
+                      builder: (BuildContext context, bool isOpen, _) {
+                        return _iconStyle.openMenuIcon != null
+                            ? isOpen
+                                ? _iconStyle.openMenuIcon!
+                                : _iconStyle.icon
+                            : _iconStyle.icon;
+                      },
+                    ),
                   ),
-                ),
-              ],
+                ],
+              ),
             ),
           ),
     );

packages/dropdown_button2/lib/src/dropdown_menu_item.dart

@@ -111,10 +111,9 @@ class _DropdownMenuItemContainer extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return Container(
+    return SizedBox(
       height: intrinsicHeight ? null : height,
-      alignment: alignment,
-      child: child,
+      child: Align(alignment: alignment, child: child),
     );
   }
 }
@@ -239,7 +238,7 @@ class _DropdownItemButtonState<T> extends State<_DropdownItemButton<T>> {
   Widget build(BuildContext context) {
     final DropdownItem<T> dropdownItem = widget.route.items[widget.itemIndex];
 
-    Widget child = Container(
+    Widget child = Padding(
       padding: (menuItemStyle.padding ?? _kMenuItemPadding)
           .resolve(widget.textDirection),
       child: dropdownItem,

packages/dropdown_button2/lib/src/utils.dart

@@ -36,6 +36,35 @@ void _uniqueValueAssert<T>(
   );
 }
 
+class _ConditionalDecoratedBox extends StatelessWidget {
+  const _ConditionalDecoratedBox({
+    required this.child,
+    this.height,
+    this.width,
+    this.decoration,
+    this.foregroundDecoration,
+  });
+
+  final double? height;
+  final double? width;
+  final Decoration? decoration;
+  final Decoration? foregroundDecoration;
+  final Widget child;
+
+  @override
+  Widget build(BuildContext context) {
+    return decoration != null || foregroundDecoration != null
+        ? Container(
+            height: height,
+            width: width,
+            decoration: decoration,
+            foregroundDecoration: foregroundDecoration,
+            child: child,
+          )
+        : SizedBox(height: height, width: width, child: child);
+  }
+}
+
 extension _InputDecorationExtension on InputDecoration {
   InputDecoration updateSurroundingElements({
     required Widget? error,