pop up menu add initValue

example/lib/example_pop_up_menu.dart

@@ -24,8 +24,12 @@ class _ExamplePopUpMenuState extends State<ExamplePopUpMenu> {
                   onPressed: () {
                     showASPopUpMenu<int>(
                       context: context,
+                      initValue: 3,
                       items: [
                         PopupMenuItem(child: 'test'.text, value: 1),
+                        PopupMenuItem(child: 'test'.text, value: 2),
+                        PopupMenuItem(child: 'test'.text, value: 3),
+                        PopupMenuItem(child: 'test'.text, value: 4),
                       ],
                     ).then((value) {});
                   },

lib/extension/num_extension.dart

@@ -14,6 +14,19 @@ extension NumExt on num {
   ///圆角
   BorderRadius get radius => BorderRadius.circular(this.w);
 
+  BorderRadius get topRadius => BorderRadius.vertical(
+        top: Radius.circular(this.w),
+      );
+  BorderRadius get bottomRadius => BorderRadius.vertical(
+        bottom: Radius.circular(this.w),
+      );
+  BorderRadius get leftRadius => BorderRadius.horizontal(
+        left: Radius.circular(this.w),
+      );
+  BorderRadius get rightRadius => BorderRadius.horizontal(
+        right: Radius.circular(this.w),
+      );
+
   ///每三位数加逗号
   String comma({int fixed = 2}) {
     bool notUseFixedFlag = fixed == -1;

lib/pop_up_menu/pop_up_menu.dart

@@ -14,11 +14,13 @@ import 'package:flutter/material.dart';
 Future<T> showASPopUpMenu<T>({
   @required BuildContext context,
   @required List<PopupMenuEntry<T>> items,
+  T initValue,
 }) async {
   final RenderBox renderBox = context.findRenderObject();
   Offset offset = renderBox.localToGlobal(Offset.zero);
   return await showMenu(
     context: context,
+    initialValue: initValue,
     position: RelativeRect.fromLTRB(
       offset.dx,
       offset.dy,