1、优化MyPageAppBar(返回箭头展示隐藏)

lib/widget/my_app_bar.dart

@@ -29,13 +29,15 @@ class MyPageAppBar extends StatelessWidget implements PreferredSizeWidget {
     return AppBar(
       key: key,
       centerTitle: true,
-      title: titleWidget ?? Text(title ?? "", style: TextStyle(color: foregroundColor)),
+      title: titleWidget ??
+          Text(title ?? "", style: TextStyle(color: foregroundColor)),
       backgroundColor: backgroundColor,
       foregroundColor: foregroundColor,
       primary: primary,
       actions: actions,
-      leading: leading,
+      leading: !showBack ? null : leading,
       elevation: elevation,
+      // If false and [leading] is null, leading space is given to [title].
       automaticallyImplyLeading: showBack,
     );
   }