如何将按钮添加到上面挂出的底部导航栏 - Flutter

Question

我有底部导航栏,中心项目如下图所示:

如何在Flutter中实现这样的事情？

我发现我放入BottomNavigatonBarItem的每个图标都符合导航栏的界限.但我需要把它挂在上面.

Answer 1

您可以Stack在彼此的顶部显示小部件.结合属性overflow:Overflow.visible和符合您需求的对齐方式.

以下示例将实现图片中的内容:水平居中的浮动按钮,顶部与底部条对齐.

return new Scaffold(
  bottomNavigationBar: new Stack(
    overflow: Overflow.visible,
    alignment: new FractionalOffset(.5, 1.0),
    children: [
      new Container(
        height: 40.0,
        color: Colors.red,
      ),
      new Padding(
        padding: const EdgeInsets.only(bottom: 12.0),
        child: new FloatingActionButton(
          notchMargin: 24.0,
          onPressed: () => print('hello world'),
          child: new Icon(Icons.arrow_back),
        ),
      ),
    ],
  ),
);

Answer 2

您也可以使用 FloatingActionButtonLocation 和 Expanded 小部件来执行此操作，如下所示：

Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text(widget.title),
      ),
      body: _buildTodoList(),
      floatingActionButton: new FloatingActionButton(
        onPressed: _pushAddTodoScreen,
        tooltip: 'Increment',
        child: new Icon(Icons.add),
        elevation: 4.0,
      ),
      bottomNavigationBar: BottomAppBar(
        child: new Row(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Expanded(child: IconButton(icon: Icon(Icons.home)),),
            Expanded(child: IconButton(icon: Icon(Icons.show_chart)),),
            Expanded(child: new Text('')),
            Expanded(child: IconButton(icon: Icon(Icons.tab)),),
            Expanded(child: IconButton(icon: Icon(Icons.settings)),),
          ],
        ),
      ),
      floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
    );
  }

预览：

Answer 3

谷歌最近添加了一个叫做的东西BottomAppBar，它提供了一种更好的方法来做到这一点。只需BottomAppBar在脚手架中添加，创建一个导航 FAB，如果您希望它有文本，则向 FAB 添加一个标签。创建与此类似的结果：https : //cdn-images-1.medium.com/max/1600/1*SEYUo6sNrW0RoKxyrYCqbg.png。

Widget build(BuildContext context) {
  return new Scaffold(
    appBar: AppBar(title: const Text('Tasks - Bottom App Bar')),
    floatingActionButton: FloatingActionButton.extended(
      elevation: 4.0,
      icon: const Icon(Icons.add),
      label: const Text('Add a task'),
      onPressed: () {},
    ),
    floatingActionButtonLocation: 
      FloatingActionButtonLocation.centerDocked,
    bottomNavigationBar: BottomAppBar(
      hasNotch: false,
      child: new Row(
        mainAxisSize: MainAxisSize.max,
        mainAxisAlignment: MainAxisAlignment.spaceBetween,
        children: <Widget>[
          IconButton(
            icon: Icon(Icons.menu),
            onPressed: () {},
          ),
          IconButton(
            icon: Icon(Icons.search),
            onPressed: () {},
          )
        ],
      ),
    ),
  );
}