你也可以使用ButtonTheme():

下面是示例代码

ButtonTheme(
    minWidth: 200.0,
    shape: RoundedRectangleBorder(
        borderRadius: BorderRadius.circular(18.0),
        side: BorderSide(color: Colors.green)),
    child: RaisedButton(
        elevation: 5.0,
        hoverColor: Colors.green,
        color: Colors.amber,
        child: Text(
            "Place Order",
            style: TextStyle(
                     color: Colors.white, fontWeight: FontWeight.bold),
        ),
        onPressed: () {},
    ),
),

你可以使用这个样式为你的elevatedButton使它成为圆形

style: ButtonStyle(
              elevation: MaterialStateProperty.all(8.0),
              backgroundColor:
                  MaterialStateProperty.all(Constants().orangeColor),
              textStyle: MaterialStateProperty.all(
                TextStyle(
                  fontSize: 16.0,
                ),
              ),
              shape: MaterialStateProperty.all<CircleBorder>(
                CircleBorder(),
              ),
              shadowColor: MaterialStateProperty.all(Constants().orangeColor),
            ),

您可以使用ElevatedButton小部件。提升的按钮小部件有一个shape属性，您可以使用该属性，如下面的代码片段所示。

ElevatedButton(
      style: ButtonStyle(
          shape: MaterialStateProperty.all<RoundedRectangleBorder>(
              RoundedRectangleBorder(
                  borderRadius: BorderRadius.circular(18.0),
                  side: BorderSide(
                      color: Colors.teal, 
                      width: 2.0,
                  ),
              ),
          ),
      ),
      child: Text('Submit'),
      onPressed: () {},
),

要在按钮中使用任何形状，请确保执行button小部件内的所有代码:

 **shape: RoundedRectangleBorder(
        borderRadius: new BorderRadius.circular(18.0),
        side: BorderSide(color: Colors.red) ),**

如果你想让它变成正方形，使用BorderRadius.circular(0.0)，它会自动把它变成正方形。

按钮是这样的:

下面是给出UI屏幕的所有源代码:

 Scaffold(
    backgroundColor: Color(0xFF8E44AD),
    body: new Center(
      child: Column(
        children: <Widget>[
          Container(
            margin: EdgeInsets.fromLTRB(90, 10, 20, 0),
            padding: new EdgeInsets.only(top: 92.0),
            child: Text(
              "Currency Converter",
              style: TextStyle(
                fontSize: 48,
                fontWeight: FontWeight.bold,
                color: Colors.white,
              ),
            ),
          ),
          Container(
            margin: EdgeInsets.only(),
            padding: EdgeInsets.all(25),
            child: TextFormField(
              decoration: new InputDecoration(
                filled: true,
                fillColor: Colors.white,
                labelText: "Amount",
                border: OutlineInputBorder(
                  borderRadius: BorderRadius.circular(10),
                ),
              ),
            ),
          ),
          Container(
            padding: EdgeInsets.all(25),
            child: TextFormField(
              decoration: new InputDecoration(
                filled: true,
                fillColor: Colors.white,
                labelText: "From",
                border: OutlineInputBorder(
                  borderRadius: BorderRadius.circular(10),
                ),
              ),
            ),
          ),
          Container(
            padding: EdgeInsets.all(25),
            child: TextFormField(
              decoration: new InputDecoration(
                  filled: true,
                  fillColor: Colors.white,
                  labelText: "To",
                  border: OutlineInputBorder(
                    borderRadius: BorderRadius.circular(10),
                  )),
            ),
          ),
          SizedBox(height: 20.0),
          MaterialButton(
            height: 58,
            minWidth: 340,
            shape: RoundedRectangleBorder(
                borderRadius: new BorderRadius.circular(12)),
            onPressed: () {},
            child: Text(
              "CONVERT",
              style: TextStyle(
                fontSize: 24,
                color: Colors.black,
              ),
            ),
            color: Color(0xFFF7CA18),
          ),
        ],
      ),
    ),
  ),
);

你可以简单地使用RaisedButton或你可以使用InkWell来获得一个自定义按钮和属性，如onDoubleTap, onLongPress等:

new InkWell(
  onTap: () => print('hello'),
  child: new Container(
    //width: 100.0,
    height: 50.0,
    decoration: new BoxDecoration(
      color: Colors.blueAccent,
      border: new Border.all(color: Colors.white, width: 2.0),
      borderRadius: new BorderRadius.circular(10.0),
    ),
    child: new Center(child: new Text('Click Me', style: new TextStyle(fontSize: 18.0, color: Colors.white),),),
  ),
),

如果你想在InkWell小部件中使用splashColor和highlightColor属性，使用Material小部件作为InkWell小部件的父部件，而不是装饰容器(删除装饰属性)。在这里阅读原因。

     Container(
        width: yourWidth,
        height: yourHeight ,
        decoration: BoxDecoration(
            borderRadius: radius,
            gradient: yourGradient,
            border: yourBorder),
        child: FlatButton(
          onPressed: {} (),
          shape: RoundedRectangleBorder(borderRadius: radius),
    .......

用同样的半径。