下面是解决问题的代码。你只需要在盒子装饰中取一个有边界半径的简单容器。

new Container(
    alignment: Alignment.center,
    decoration: BoxDecoration(
        borderRadius: BorderRadius.all(Radius.circular(15.0)),
        color: Colors.blue,
    ),

    child: Row(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
            Padding(
                padding: const EdgeInsets.all(10.0),
                child: new Text(
                    "Next",
                    style: new TextStyle(
                        fontWeight: FontWeight.w500,
                        color: Colors.white,
                        fontSize: 15.0,
                    ),
                ),
            ),
        ],
    ),
),

使用Flutter版本2，请尝试以下操作

ElevatedButton(
    style: ButtonStyle(
        shape: MaterialStateProperty.all<OutlinedBorder>(
            RoundedRectangleBorder(
                side:
                    BorderSide(width: 1.0, color: Colors.red,
                borderRadius:
                    BorderRadius.circular(5.0),),),
        backgroundColor: MaterialStateProperty.all<Color>(Colors.red),
        foregroundColor: MaterialStateProperty.all<Color>(Colors.green),
        elevation:
            MaterialStateProperty.all<double>(8.0),
        padding: MaterialStateProperty.all<EdgeInsetsGeometry>(
            const EdgeInsets.symmetric(
                horizontal: 15.0,
                vertical: 10.0),),),
    onPressed: (){},
    child: Text('Button'),)

试试这个:

SizedBox(
  height: 40.0,
  child: MaterialButton(
    child: Text("Button"),
    color: Colors.blue,
    disabledColor: Colors.blue,
    shape: RoundedRectangleBorder(
      borderRadius: BorderRadius.all(
        Radius.circular(10.0), // Change your border radius here
      ),
    ),
    onPressed: () {},
  ),
),

在容器小部件中包装一个TextButton，如下所示:

Container(
  decoration: BoxDecoration(
    borderRadius: BorderRadius.circular(5),
    border: Border.all(color: Colors.black),
  ),
  child: TextButton(
    onPressed: () {
      // To do
    },
    child: Text("Go to Change Language Screen "),
  ),
)

你可以使用下面的代码:

ElevatedButton(
      onPressed: () {},
      style: ElevatedButton.styleFrom(
        shape: RoundedRectangleBorder(
            borderRadius: BorderRadius.all(Radius.circular(borderRadius))),
      ),
      child: Text("ok"),
    )

如果有人正在寻找完整的圆形按钮，那么我实现它的方式:

Center(
            child: SizedBox.fromSize(
              size: Size(80, 80), // Button width and height
              child: ClipOval(
                child: Material(
                  color: Colors.pink[300], // Button color
                  child: InkWell(
                    splashColor: Colors.yellow, // splash color
                    onTap: () {}, // Button pressed
                    child: Column(
                      mainAxisAlignment: MainAxisAlignment.center,
                      children: <Widget>[
                        Icon(Icons.linked_camera), // Icon
                        Text("Picture"), // Text
                      ],
                    ),
                  ),
                ),
              ),
            ),
          )