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

}

圆边颜色容器:

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

在Null安全之后，使用ElevatedButton而不是RaisedButton，因为RaisedButton就像文档中说的那样被贬低了。

             child: ElevatedButton(
                onPressed: () {},
                child: const Text('Add item to the list'),
                style: ButtonStyle(
                  backgroundColor:
                      MaterialStateProperty.all<Color>(Common.buttonColor),
                  shape: MaterialStateProperty.all<RoundedRectangleBorder>(
                    RoundedRectangleBorder(
                      borderRadius: BorderRadius.circular(18.0),
                    ),
                  ),
                ),
              ),

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
    )
  ]
)

现在我们有一个图标按钮来实现圆形按钮点击和覆盖。但是，背景颜色还不可用，但同样可以通过Circle头像小部件实现，如下所示:

CircleAvatar(
    backgroundColor: const Color(0xffF4F3FA),
    child: IconButton(
        onPressed: () => FlushbarHelper.createInformation(
                             message: 'Work in progress...')
                             .show(context),
        icon: Icon(Icons.more_vert),
    ),
),

还有另一种方法来做到这一点-只是使用FloatingActionButton适当的圆形按钮。

Scaffold(
      appBar: AppBar(
        title: const Text('Floating Action Button'),
      ),
      body: const Center(child: Text('Press the button below!')),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          // Add your onPressed code here!
        },
        backgroundColor: Colors.green,
        child: const Icon(Icons.navigation),
      ),
    )