如何在函数中获取上下文？

Question

我需要为我的 Navigator 推送获取上下文，我的函数 _navigate 上有这个 Navigator。我尝试了类似 _navigate(BuildContext context) 但我得到了一个错误，比如“type (BuildContext) => dynamic is not a subtype of type() => void。这是 Navigator.push 的第一个上下文我不知道如何得到它。

import 'package:flutter/material.dart';
import 'package:pandora_etna/assistance.dart';
import 'dart:math';
import 'package:vector_math/vector_math.dart' show radians;
import 'package:font_awesome_flutter/font_awesome_flutter.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
          backgroundColor: Color(0xFFB3E5FC),
          body: SizedBox.expand(child: RadialMenu())),
    );
  }
}

class RadialMenu extends StatefulWidget {
  createState() => _RadialMenuState();
}

class _RadialMenuState extends State<RadialMenu>
    with SingleTickerProviderStateMixin {
  AnimationController controller;

  void initState() {
    super.initState();
    controller =
        AnimationController(duration: Duration(milliseconds: 900), vsync: this);
  }

  Widget build(BuildContext context) {
    return RadialAnimation(controller: controller);
  }
}

class RadialAnimation extends StatelessWidget {
  RadialAnimation({Key key, this.controller})
      : scale = Tween<double>(
          begin: 1.5,
          end: 0.0,
        ).animate(
          CurvedAnimation(parent: controller, curve: Curves.fastOutSlowIn),
        ),
        translation = Tween<double>(
          begin: 0.0,
          end: 100.0,
        ).animate(
          CurvedAnimation(parent: controller, curve: Curves.linear),
        ),
        rotation = Tween<double>(begin: 0.0, end: 360.0).animate(
          CurvedAnimation(
              parent: controller,
              curve: Interval(
                0.0,
                0.7,
                curve: Curves.decelerate,
              )),
        ),
        super(key: key);

  final AnimationController controller;
  final Animation<double> scale;
  final Animation<double> translation;
  final Animation<double> rotation;

  build(context) {
    return AnimatedBuilder(
        animation: controller,
        builder: (context, builder) {
          return Transform.rotate(
              angle: radians(rotation.value),
              child: Stack(alignment: Alignment.center, children: [
                _buildButton(0, _close,
                    color: Color(0xFF29B6F6), icon: FontAwesomeIcons.chartBar),
                _buildButton(60, _close,
                    color: Color(0xFF29B6F6), icon: FontAwesomeIcons.clipboard),
                _buildButton(120, _close,
                    color: Color(0xFF29B6F6), icon: FontAwesomeIcons.chartBar),
                _buildButton(180, _close,
                    color: Color(0xFF29B6F6), icon: FontAwesomeIcons.book),
                _buildButton(240, _close,
                    color: Color(0xFF29B6F6),
                    icon: FontAwesomeIcons.arrowsAltV),
                _buildButton(300, _navigate,
                    color: Color(0xFF29B6F6), icon: FontAwesomeIcons.phoneAlt),
                _buildButton(360, _close,
                    color: Color(0xFF29B6F6),
                    icon: FontAwesomeIcons.compressAlt),
                Transform.scale(
                  scale: scale.value - 1.5,
                  child: FloatingActionButton(
                      child: Icon(FontAwesomeIcons.timesCircle),
                      onPressed: _close,
                      backgroundColor: Color(0xFF29B6F6)),
                ),
                Transform.scale(
                  scale: scale.value,
                  child: FloatingActionButton(
                      child: Icon(FontAwesomeIcons.solidDotCircle),
                      onPressed: _open,
                      backgroundColor: Color(0xFF29B6F6)),
                ),
              ]));
        });
  }

  _buildButton(double angle, Function callback, {Color color, IconData icon}) {
    final double rad = radians(angle);
    return Transform(
        transform: Matrix4.identity()
          ..translate(
              (translation.value) * cos(rad), (translation.value) * sin(rad)),
        child: FloatingActionButton(
            child: Icon(icon), backgroundColor: color, onPressed: callback));
  }

  _open() {
    controller.forward();
  }

  _close() {
    controller.reverse();
  }

  _navigate(BuildContext context) {
    Navigator.push(
        context, new MaterialPageRoute(builder: (context) => Assistance()));
  }
}

Answer 1

当调用你的函数 _buildButton 时，你必须将 _navigate 函数包装到另一个函数中，因为它需要你当前的上下文才能工作
试试这个

_buildButton(300, () {
   _navigate(context);
}, color: Color(0xFF29B6F6), icon: FontAwesomeIcons.phoneAlt),

Answer 2

我认为这是因为您在调用 _buildButton 时丢失了 context 参数。

/// By writing your Function parameter like this you will pass the
/// BuildContext parameter needed.
_buildButton(
   300,
   () => _navigate(context),
   color: Color(0xFF29B6F6),
   icon: FontAwesomeIcons.phoneAlt
),

Answer 3

您需要在引用时将 BuildContext 传递给 _navigate 函数。您可以使用匿名函数来执行此操作。 _buildButton(300,(context) => _navigate(context), ...

Answer 4

Try out below example for more idea:-

 _buildButton(300, _navigate(context),   // Added Context here,It will contains context of build function 
                    color: Color(0xFF29B6F6), icon: FontAwesomeIcons.phoneAlt),

  _navigate(BuildContext context) {
    Navigator.push(
        context, new MaterialPageRoute(builder: (context) => Assistance()));
  }

Answer 5

它不起作用，因为您没有给出函数方法的上下文参数。我想是的

      _buildButton(300, _navigate(context),
                color: Color(0xFF29B6F6), icon: FontAwesomeIcons.phoneAlt),