如何在flutter的scaffold中设置"FloatingActionButtonLocation"的自定义偏移量？

Question

最近引入了FloatingActionButtonLocation，它有四个值，都用于底部对齐。我想把它放在顶部，在应用栏下方中间位置。但是我无法找到如何设置自定义偏移量的方法。官方文档也很缺乏相关说明。

- AgentTango

Answer 1

这违反了材料设计指南。但您可以通过更改原始源代码中的 scaffoldGeometry.contentBottom 为 scaffoldGeometry.contentTop 来实现这一点。下面的代码应该可行。

import 'package:flutter/material.dart';
import 'dart:math' as math;


class HomeHeader extends StatefulWidget {
  final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
  @override
  HomeHeaderState createState() {
    return new HomeHeaderState();
  }
}

class HomeHeaderState extends State<HomeHeader> {

  static const FloatingActionButtonLocation centerDocked = _CenterDockedFloatingActionButtonLocation();

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      key: widget._scaffoldKey,
      appBar: AppBar(
        title: Text('duh'),
      ),
      floatingActionButtonLocation:centerDocked,
      floatingActionButton: FloatingActionButton(
        child: const Icon(Icons.add), onPressed: () {

      },),
      body: new Container()
    );
  }
}
class _CenterDockedFloatingActionButtonLocation extends _DockedFloatingActionButtonLocation {
  const _CenterDockedFloatingActionButtonLocation();

  @override
  Offset getOffset(ScaffoldPrelayoutGeometry scaffoldGeometry) {
    final double fabX = (scaffoldGeometry.scaffoldSize.width - scaffoldGeometry.floatingActionButtonSize.width) / 2.0;
    return Offset(fabX, getDockedY(scaffoldGeometry));
  }
}

abstract class _DockedFloatingActionButtonLocation extends FloatingActionButtonLocation {
  const _DockedFloatingActionButtonLocation();
  @protected
  double getDockedY(ScaffoldPrelayoutGeometry scaffoldGeometry) {
    final double contentBottom = scaffoldGeometry.contentTop;
    final double appBarHeight = scaffoldGeometry.bottomSheetSize.height;
    final double fabHeight = scaffoldGeometry.floatingActionButtonSize.height;
    final double snackBarHeight = scaffoldGeometry.snackBarSize.height;

    double fabY = contentBottom - fabHeight / 2.0;
    if (snackBarHeight > 0.0)
      fabY = math.min(fabY, contentBottom - snackBarHeight - fabHeight - kFloatingActionButtonMargin);
    if (appBarHeight > 0.0)
      fabY = math.min(fabY, contentBottom - appBarHeight - fabHeight / 2.0);

    final double maxFabY = scaffoldGeometry.scaffoldSize.height - fabHeight;
    return math.min(maxFabY, fabY);
  }
}

- a0x2

---

谢谢，这对我有用！不过，我做了一些简化，将FAB放在宽度的25％和75％处。 - Sheruan Bashar

Answer 2

不要使用内置的FAB，而是使用自己的圆形按钮堆栈。在你的脚手架主体中，你可以这样做：

  body: Stack(
    children: <Widget>[

      Container(
        // whatever your main content is
      ),

      Positioned(
        top: 5.0,
        right: 200.0, // or whatever
        child: MyFAB,
      ),
    ],
  ),

然后，MyFAB 可以是这样的：

class MyFAB extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return Container(

      color: Colors.blue,
      child: InkWell(
        onTap: () => {},
        borderRadius: BorderRadius.circular(50.0),
        child: Container(
          width: 45.0,
          height: 45.0,
          decoration: BoxDecoration(
            shape: BoxShape.circle,
            color: Colors.red,
          ),
          child: Icon(
            Icons.add,
            color: Colors.yellow,
            size: 25.0,
          ),
        ),
      ),
    );
  }
}

使用 Stack 中的 Positioned widget，您现在可以将 FAB 放置在任何位置。

- blaneyneil