在AppBar中颤动自定义操作

问题描述

为了在整个应用程序中拥有相同的AppBar，我创建了一个单独的文件，其中包含要包含在每个屏幕中的AppBar.也可以传递一些变量，例如:action.因此，对于不同的屏幕，我仍可以在同一AppBar中进行不同的操作.所有这些工作正常，如下面的代码所示.但是，如果没有传递任何动作( dropdownChoices.length == 0 )，如何在AppBar中隐藏动作?

In order to have the same AppBar through my whole application, I created a separated file containing the AppBar which I include in every screen. It is also possible to pass some variables e.g.: actions. So for different screens I can have different actions still within the same AppBar. All this works fine like shown in the code below. But how to hide the Actions in the AppBar when there are no actions passed (dropdownChoices.length == 0)?

class BaseAppBar extends StatelessWidget implements PreferredSizeWidget {
  final Color bgColor = HexToColor('#508bbb');
  final String title;
  final AppBar appBar;
  final TabBar tabBar;
  final List<DropdownChoices> dropdownChoices;
  final bool isHomepage;
  final bool goBack;

  final PageRouteBuilder _homeRoute = new PageRouteBuilder(
    pageBuilder: (BuildContext context, _, __) {
      return HomePage();
    },
  );

  BaseAppBar(
      {Key key,
      this.title,
      this.appBar,
      this.tabBar,
      this.dropdownChoices,
      this.isHomepage = false,
      this.goBack = false})
      : super(key: key);

  @override
  Widget build(BuildContext context) {
    return ...
      actions: <Widget>[
        PopupMenuButton<DropdownChoices>(
          onSelected: (value) {
            if (value.action == 'refresh') {
              Navigator.pushReplacementNamed(context, value.route);
            }
          },
          elevation: 6,
          itemBuilder: (BuildContext context) {
            return dropdownChoices.map((DropdownChoices choice) {
              return PopupMenuItem<DropdownChoices>(
                value: choice,
                child: Text(choice.title),
              );
            }).toList();
          },
        )
      ],
    );
  }
}

class DropdownChoices {
  const DropdownChoices({this.title, this.action, this.route});

  final String title;
  final String action;
  final String route;
}

推荐答案

我倾向于尝试类似

actions: (dropdownChoices.length < 1) ? null : <Widget>[
  PopupMenuButton<DropdownChoices>(...),
],

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