dart - 确定在运行时构造哪种类型

我正在尝试更多地了解Flutter。

我有一个按钮类，它可以根据参数构建FlatButton或OutlineButton

import 'package:flutter/material.dart';

class Button extends StatelessWidget {
  final String text;
  final VoidCallback onPressed;
  final Color backgroundColor;
  final Color textColor;
  final bool isOutline;

  Button(
      {@required this.text,
      @required this.onPressed,
      this.backgroundColor = Colors.deepOrange,
      this.textColor = Colors.white,
      this.isOutline = false});

  @override
  Widget build(BuildContext context) {
    return this.isOutline
        ? _buildOutlineButton(context)
        : _buildFlatButton(context);
  }

  FlatButton _buildFlatButton(BuildContext context) {
    return FlatButton(
      shape: RoundedRectangleBorder(
        borderRadius: BorderRadius.circular(30.0),
      ),
      color: this.backgroundColor,
      onPressed: this.onPressed,
      child: Container(
        padding: const EdgeInsets.symmetric(
          vertical: 20.0,
          horizontal: 20.0,
        ),
        child: Row(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Expanded(
              child: Text(
                this.text,
                textAlign: TextAlign.center,
                style:
                    TextStyle(color: this.textColor, fontWeight: FontWeight.bold),
              ),
            ),
          ],
        ),
      ),
    );
  }

  OutlineButton _buildOutlineButton(BuildContext context) {
    return OutlineButton(
      shape: RoundedRectangleBorder(
        borderRadius: BorderRadius.circular(30.0),
      ),
      color: this.backgroundColor,
      onPressed: this.onPressed,
      child: Container(
        padding: const EdgeInsets.symmetric(
          vertical: 20.0,
          horizontal: 20.0,
        ),
        child: Row(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Expanded(
              child: Text(
                this.text,
                textAlign: TextAlign.center,
                style:
                    TextStyle(color: this.textColor, fontWeight: FontWeight.bold),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

如您所见，这两个_build*Button函数看起来都很相似。有没有一种方法可以简单地编写代码？这样的东西(前面的伪代码):

final type = this.isOutline ? OutlineButton : FlatButton;
return type(shape: ..., color: ..., ...);

---

Best Answer-推荐答案

您可以像这样共享许多通用代码:

  MaterialButton _buildButton(bool flat, BuildContext context) {
    Container container = Container(
      padding: const EdgeInsets.symmetric(
        vertical: 20.0,
        horizontal: 20.0,
      ),
      child: Row(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          Expanded(
            child: Text(
              text,
              textAlign: TextAlign.center,
              style: TextStyle(color: textColor, fontWeight: FontWeight.bold),
            ),
          ),
        ],
      ),
    );
    RoundedRectangleBorder border = RoundedRectangleBorder(
      borderRadius: BorderRadius.circular(30.0),
    );
    return flat
        ? FlatButton(
            shape: border,
            color: backgroundColor,
            onPressed: onPressed,
            child: container,
          )
        : RaisedButton(
            shape: border,
            color: backgroundColor,
            onPressed: onPressed,
            child: container,
          );
  }

关于dart - 确定在运行时构造哪种类型，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/55052842/