1、优化MyPageAppBar(返回箭头展示隐藏)

lib/widget/my_app_bar.dart

@@ -4,7 +4,7 @@ class MyPageAppBar extends StatelessWidget implements PreferredSizeWidget {
   final String? title; // 标题
   final Color? backgroundColor; // 背景颜色
   final Color? foregroundColor; // 前景颜色
-  final bool showBack;  // 是否展示返回箭头
+  final bool showBack; // 是否展示返回箭头
   final bool primary;
   final List<Widget>? actions; // 右侧widget
   final Widget? leading; // 左侧widget
@@ -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,
     );
   }