RaisedButton(
          child: Text("Button"),
          onPressed: (){},
          shape: RoundedRectangleBorder(borderRadius: new BorderRadius.circular(30.0),
          side: BorderSide(color: Colors.red))
        )

圆边颜色容器:

Container(
  decoration: BoxDecoration(
    borderRadius: BorderRadius.circular(10),
    border: Border.all(color: Colors.red),
  ),
  child: Text("Some Text"),
)

另一个很酷的解决方案在2021年也适用:

TextButton(
    child: Padding(
        padding: const EdgeInsets.all(5.0),
        child: Text('Follow Us'.toUpperCase()),
    ),
    style: TextButton.styleFrom(
        backgroundColor: Colors.amber,
        shadowColor: Colors.red,
        elevation: 2,
        textStyle: TextStyle(fontSize: 18, fontWeight: FontWeight.bold),
        shape: RoundedRectangleBorder(
            borderRadius: BorderRadius.circular(5.0),)
    ),
    onPressed: () {
        print('Pressed');
    },
),

addButton() {
return Row(
  mainAxisAlignment: MainAxisAlignment.center,
  children: <Widget>[
    Padding(
      padding: const EdgeInsets.symmetric(vertical: 10.0),
      child: SizedBox(
        height: 45,
        width: 200,
        child: ElevatedButton.icon(
          onPressed: () async {},
          style: ButtonStyle(
            shape: MaterialStateProperty.all<RoundedRectangleBorder>(
                RoundedRectangleBorder(
                    borderRadius: BorderRadius.circular(30.0),
                  )),
            elevation: MaterialStateProperty.all(1),
            backgroundColor: MaterialStateProperty.all(Colors.blue),
          ),
          icon: Icon(Icons.add, size: 18),
          label: Text("Add question"),
        ),
      ),
    ),
  ],
);

}

1. 解决方案概述

FlatButton和RaisedButton已弃用。

因此，你可以使用形状放在样式属性，为TextButton和ElevatedButton。

自Flutter 2.0以来有一些变化:

style:属性类型已更改为ButtonStyle shape:属性类型已更改为MaterialStateProperty<T>

2. 圆形的按钮

在style属性中存在shape属性:

style: ButtonStyle(
  shape: MaterialStateProperty.all<RoundedRectangleBorder>(
    RoundedRectangleBorder(
      borderRadius: BorderRadius.circular(18.0),
      side: BorderSide(color: Colors.red)
    )
  )
)

方形按钮

对于方形按钮，您可以使用ElevatedButton或添加其他方式:

style: ButtonStyle(
  shape: MaterialStateProperty.all<RoundedRectangleBorder>(
    RoundedRectangleBorder(
      borderRadius: BorderRadius.zero,
      side: BorderSide(color: Colors.red)
    )
  )
)

完整的示例

Row(
  mainAxisAlignment: MainAxisAlignment.end,
  children: [
    TextButton(
      child: Text(
        "Add to cart".toUpperCase(),
        style: TextStyle(fontSize: 14)
      ),
      style: ButtonStyle(
        padding: MaterialStateProperty.all<EdgeInsets>(EdgeInsets.all(15)),
        foregroundColor: MaterialStateProperty.all<Color>(Colors.red),
        shape: MaterialStateProperty.all<RoundedRectangleBorder>(
          RoundedRectangleBorder(
            borderRadius: BorderRadius.circular(18.0),
            side: BorderSide(color: Colors.red)
          )
        )
      ),
      onPressed: () => null
    ),
    SizedBox(width: 10),
    ElevatedButton(
      child: Text(
        "Buy now".toUpperCase(),
        style: TextStyle(fontSize: 14)
      ),
      style: ButtonStyle(
        foregroundColor: MaterialStateProperty.all<Color>(Colors.white),
        backgroundColor: MaterialStateProperty.all<Color>(Colors.red),
        shape: MaterialStateProperty.all<RoundedRectangleBorder>(
          RoundedRectangleBorder(
            borderRadius: BorderRadius.zero,
            side: BorderSide(color: Colors.red)
          )
        )
      ),
      onPressed: () => null
    )
  ]
)

创建圆角按钮的不同方法如下:

用ElevatedButton. stylefrom

ElevatedButton(
          style: ElevatedButton.styleFrom(
            shape: RoundedRectangleBorder(
              borderRadius: BorderRadius.circular(30.0),
            ),
          ),
          onPressed: () {},
          child:
              Text("Buy now".toUpperCase(), style: TextStyle(fontSize: 14)),
        ),

用ButtonStyle提升按钮

ElevatedButton(
          style: ButtonStyle(
              shape: MaterialStateProperty.all<RoundedRectangleBorder>(
                  RoundedRectangleBorder(
            borderRadius: BorderRadius.circular(50.0),
          ))),
          onPressed: () {},
          child: Text("Submit".toUpperCase()),
        ),

圆形按钮的实际演示可以在下面的Dartpad链接中找到:

圆形按钮演示例子在达特pad