Add requestFocusOnTap to DropdownMenu (#117504)

* Add canRequestFocus to TextField and requestFocusOnTap to DropdownMenu

* Address comments

* Address comments

---------

Co-authored-by: Qun Cheng <quncheng@google.com>

Author: QuncCccccc

examples/api/lib/material/dropdown_menu/dropdown_menu.0.dart

@@ -67,7 +67,9 @@ class _DropdownMenuExampleState extends State<DropdownMenuExample> {
                       leadingIcon: const Icon(Icons.search),
                       label: const Text('Icon'),
                       dropdownMenuEntries: iconEntries,
-                      inputDecorationTheme: const InputDecorationTheme(filled: true),
+                      inputDecorationTheme: const InputDecorationTheme(
+                        filled: true,
+                        contentPadding: EdgeInsets.symmetric(vertical: 5.0)),
                       onSelected: (IconLabel? icon) {
                         setState(() {
                           selectedIcon = icon;

packages/flutter/lib/src/material/dropdown_menu.dart

@@ -135,6 +135,7 @@ class DropdownMenu<T> extends StatefulWidget {
     this.controller,
     this.initialSelection,
     this.onSelected,
+    this.requestFocusOnTap,
     required this.dropdownMenuEntries,
   });
 
@@ -228,6 +229,19 @@ class DropdownMenu<T> extends StatefulWidget {
   /// Defaults to null. If null, only the text field is updated.
   final ValueChanged<T?>? onSelected;
 
+  /// Determine if the dropdown button requests focus and the on-screen virtual
+  /// keyboard is shown in response to a touch event.
+  ///
+  /// By default, on mobile platforms, tapping on the text field and opening
+  /// the menu will not cause a focus request and the virtual keyboard will not
+  /// appear. The default behavior for desktop platforms is for the dropdown to
+  /// take the focus.
+  ///
+  /// Defaults to null. Setting this field to true or false, rather than allowing
+  /// the implementation to choose based on the platform, can be useful for
+  /// applications that want to override the default behavior.
+  final bool? requestFocusOnTap;
+
   /// Descriptions of the menu items in the [DropdownMenu].
   ///
   /// This is a required parameter. It is recommended that at least one [DropdownMenuEntry]
@@ -242,7 +256,6 @@ class DropdownMenu<T> extends StatefulWidget {
 class _DropdownMenuState<T> extends State<DropdownMenu<T>> {
   final GlobalKey _anchorKey = GlobalKey();
   final GlobalKey _leadingKey = GlobalKey();
-  final FocusNode _textFocusNode = FocusNode();
   final MenuController _controller = MenuController();
   late final TextEditingController _textEditingController;
   late bool _enableFilter;
@@ -288,6 +301,23 @@ class _DropdownMenuState<T> extends State<DropdownMenu<T>> {
     }
   }
 
+  bool canRequestFocus() {
+    if (widget.requestFocusOnTap != null) {
+      return widget.requestFocusOnTap!;
+    }
+
+    switch (Theme.of(context).platform) {
+      case TargetPlatform.iOS:
+      case TargetPlatform.android:
+      case TargetPlatform.fuchsia:
+        return false;
+      case TargetPlatform.macOS:
+      case TargetPlatform.linux:
+      case TargetPlatform.windows:
+        return true;
+    }
+  }
+
   void refreshLeadingPadding() {
     WidgetsBinding.instance.addPostFrameCallback((_) {
       setState(() {
@@ -428,7 +458,6 @@ class _DropdownMenuState<T> extends State<DropdownMenu<T>> {
 
   @override
   void dispose() {
-    _textEditingController.dispose();
     super.dispose();
   }
 
@@ -489,13 +518,12 @@ class _DropdownMenuState<T> extends State<DropdownMenu<T>> {
           builder: (BuildContext context, MenuController controller, Widget? child) {
             assert(_initialMenu != null);
             final Widget trailingButton = Padding(
-              padding: const EdgeInsets.symmetric(horizontal: 4.0),
+              padding: const EdgeInsets.all(4.0),
               child: IconButton(
                 isSelected: controller.isOpen,
                 icon: widget.trailingIcon ?? const Icon(Icons.arrow_drop_down),
                 selectedIcon: widget.selectedTrailingIcon ?? const Icon(Icons.arrow_drop_up),
                 onPressed: () {
-                  _textFocusNode.requestFocus();
                   handlePressed(controller);
                 },
               ),
@@ -511,7 +539,9 @@ class _DropdownMenuState<T> extends State<DropdownMenu<T>> {
               width: widget.width,
               children: <Widget>[
                 TextField(
-                  focusNode: _textFocusNode,
+                  canRequestFocus: canRequestFocus(),
+                  enableInteractiveSelection: canRequestFocus(),
+                  textAlignVertical: TextAlignVertical.center,
                   style: effectiveTextStyle,
                   controller: _textEditingController,
                   onEditingComplete: () {

packages/flutter/lib/src/material/text_field.dart

@@ -312,6 +312,7 @@ class TextField extends StatefulWidget {
     this.scribbleEnabled = true,
     this.enableIMEPersonalizedLearning = true,
     this.contextMenuBuilder = _defaultContextMenuBuilder,
+    this.canRequestFocus = true,
     this.spellCheckConfiguration,
     this.magnifierConfiguration,
   }) : assert(obscuringCharacter.length == 1),
@@ -762,6 +763,13 @@ class TextField extends StatefulWidget {
   ///  * [AdaptiveTextSelectionToolbar], which is built by default.
   final EditableTextContextMenuBuilder? contextMenuBuilder;
 
+  /// Determine whether this text field can request the primary focus.
+  ///
+  /// Defaults to true. If false, the text field will not request focus
+  /// when tapped, or when its context menu is displayed. If false it will not
+  /// be possible to move the focus to the text field with tab key.
+  final bool canRequestFocus;
+
   static Widget _defaultContextMenuBuilder(BuildContext context, EditableTextState editableTextState) {
     return AdaptiveTextSelectionToolbar.editableText(
       editableTextState: editableTextState,
@@ -976,15 +984,15 @@ class _TextFieldState extends State<TextField> with RestorationMixin implements
     if (widget.controller == null) {
       _createLocalController();
     }
-    _effectiveFocusNode.canRequestFocus = _isEnabled;
+    _effectiveFocusNode.canRequestFocus = widget.canRequestFocus && _isEnabled;
     _effectiveFocusNode.addListener(_handleFocusChanged);
   }
 
   bool get _canRequestFocus {
     final NavigationMode mode = MediaQuery.maybeNavigationModeOf(context) ?? NavigationMode.traditional;
     switch (mode) {
       case NavigationMode.traditional:
-        return _isEnabled;
+        return widget.canRequestFocus && _isEnabled;
       case NavigationMode.directional:
         return true;
     }