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),
          ),
        ],
      ),
    ),
  ),
);

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

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: () {},
  ),
),

你可以创建一个自定义的视图，并把它放在一个姿态检测器中，让它表现得像一个按钮。这样做的好处是，您可以为容器提供无尽的自定义装饰类型(包括使其具有指定半径的圆形)。

如果你使用材质应用程序作为你的主小部件，你总是可以使用材质按钮。

Padding(
  padding: EdgeInsets.symmetric(vertical: 16.0),
  child: Material(
    borderRadius: BorderRadius.circular(30.0),//Set this up for rounding corners.
    shadowColor: Colors.lightBlueAccent.shade100,
    child: MaterialButton(
      minWidth: 200.0,
      height: 42.0,
      onPressed: (){//Actions here//},
      color: Colors.lightBlueAccent,
      child: Text('Log in', style: TextStyle(color: Colors.white),),
    ),
  ),
)

您可以简单地使用RaisedButton

Padding(
  padding: EdgeInsets.only(left: 150.0, right: 0.0),
  child: RaisedButton(
    textColor: Colors.white,
    color: Colors.black,
    child: Text("Search"),
    onPressed: () {},
    shape: new RoundedRectangleBorder(
      borderRadius: new BorderRadius.circular(30.0),
    ),
  ),
)

输出:

更多信息:RSCoder