flutter button
button类型：

RaisedButton ：    凸起的按钮，其实就是Android中的Material Design风格的Button ，继承自MaterialButton
FlatButton ：        扁平化的按钮，继承自MaterialButton
OutlineButton    ：带边框的按钮，继承自MaterialButton
IconButton    ：    图标按钮,继承自StatelessWidget

shape:属性

 BeveledRectangleBorder 带斜角的长方形边框
 CircleBorder 圆形边框
 RoundedRectangleBorder 圆角矩形
 StadiumBorder 两端是半圆的边框

eg:

FlatButton(
      child: Text('SimpleDialog'),
           color: Colors.green,
          // highlightColor: Colors.transparent,
             splashColor: Colors.transparent,
             shape: StadiumBorder(),  //两边圆角
             onPressed: () {              
                   },
)

去除水波纹效果
splashColor: Colors.transparent,

自定义带渐变色button

import 'package:flutter/material.dart';

class GradientButton extends StatelessWidget {
  GradientButton({
    this.colors,
    this.width,
    this.height,
    this.onTap,
    @required this.child,
  });

  // 渐变色数组
  final List<Color> colors;

  // 按钮宽高
  final double width;
  final double height;

  final Widget child;

  //点击回调
  final GestureTapCallback onTap;

  @override
  Widget build(BuildContext context) {
    ThemeData theme = Theme.of(context);

    //确保colors数组不空
    List<Color> _colors = colors ??
        [theme.primaryColor, theme.primaryColorDark ?? theme.primaryColor];

    return DecoratedBox(
      decoration: BoxDecoration(
        gradient: LinearGradient(colors: _colors),
      ),
      child: Material(
        type: MaterialType.transparency,
        child: InkWell(
          splashColor: colors.last,
          highlightColor: Colors.transparent,
          onTap: onTap,
          child: ConstrainedBox(
            constraints: BoxConstraints.tightFor(height: height, width: width),
            child: Center(
              child: Padding(
                padding: const EdgeInsets.all(8.0),
                child: DefaultTextStyle(
                    style: TextStyle(fontWeight: FontWeight.bold),
                    child: child),
              ),
            ),
          ),
        ),
      ),
    );
  }
}