Merge pull request #575 from 1jialong/fix/dropdown-single-select

DropdownMenu: 修复特定情况下的单选失效

Author: Luozf12345

tdesign-component/lib/src/components/dropdown_menu/td_dropdown_item.dart

@@ -343,8 +343,8 @@ class _TDDropdownItemState extends State<TDDropdownItem> {
 
   void _handleSelectChange(selected) {
     var isRadio = widget.multiple != true && selected is List<String>;
-    if (isRadio) {
-      selected.removeAt(0);
+    if (isRadio && selected.isNotEmpty) {
+      selected = [selected.last];
     }
     widget.options?.forEach((element) {
       element.selected = selected is List<String> ? selected.contains(element.value) : element.value == selected;
@@ -353,7 +353,7 @@ class _TDDropdownItemState extends State<TDDropdownItem> {
       setState(() {});
     }
     widget.onChange?.call(_getSelected(widget.options).map((e) => e!.value).toList());
-    if (widget.multiple != true) {
+    if (widget.multiple != true && selected.isNotEmpty) {
       _handleClose();
     }
   }