如何将按钮放在屏幕的两端

Question

我希望颤动上的按钮是屏幕的两侧，即右下方一个，一个在左下方。

我想要屏幕左侧的负按钮：

我已经在线搜索，但是找不到任何帮助，我试图使用Align，但这只是有些混乱。

我的扑来代码是（演示应用程序中的某些更改并使用Align）：

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.red,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }
  void _decrementCounter(){
    setState(() {
      -_counter --;
    });
  }
  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton:
          Row(
          mainAxisAlignment: MainAxisAlignment.end,
          children  :
        [
          Align(
              alignment: Alignment.bottomLeft,
            child : FloatingActionButton(
            onPressed: _decrementCounter,
            tooltip: 'decrement',
            child: const Icon(Icons.remove),
            heroTag: null,
          )),
          FloatingActionButton(

          onPressed: _incrementCounter,
          tooltip: 'Increment',
          child: const Icon(Icons.add),
          heroTag: null,
          )    ,
      ]),

    // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

我该如何实现？

Answer 1

一个选项是使用mainaxisAlignment：mainaxisalignment.spacebetween在row> row widget中，与setter floatingActionButtonLocation结合使用：floatingActionButtonLocation.ceentActionButtonLocation.CenterFloat。您可以使用填充水平添加一些空间：

floatingActionButtonLocation: FloatingActionButtonLocation.centerFloat,
floatingActionButton: Padding(
    padding: const EdgeInsets.symmetric(horizontal: 16.0),
    child:
        Row(mainAxisAlignment: MainAxisAlignment.spaceBetween, children: [
      FloatingActionButton(
        onPressed: _decrementCounter,
        tooltip: 'decrement',
        child: const Icon(Icons.remove),
        heroTag: null,
      ),
      FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
        heroTag: null,
      ),
    ])),

但是您使用Align也可以使用原始计划，您只需要将两个Fabs放入stack 窗口小部件，这意味着它们将彼此放置（如层），您可以分别设置左下和右下对齐：

floatingActionButtonLocation: FloatingActionButtonLocation.centerFloat,
floatingActionButton: Padding(
    padding: const EdgeInsets.symmetric(horizontal: 16.0),
    child: Stack(children: [
      Align(
          alignment: Alignment.bottomLeft,
          child: FloatingActionButton(
            onPressed: _decrementCounter,
            tooltip: 'decrement',
            child: const Icon(Icons.remove),
            heroTag: null,
          )),
      Align(
          alignment: Alignment.bottomRight,
          child: FloatingActionButton(
            onPressed: _incrementCounter,
            tooltip: 'Increment',
            child: const Icon(Icons.add),
            heroTag: null,
          )),
    ])),