DropDownButton

DropDownButton可以实现一个下拉框效果的按钮。

 int selectedValue = 1;
 
@override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('title'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text('You have pushed this button many times'),
            Text('test2'),
            DropdownButton(
                value: selectedValue,
                items: const [
                  DropdownMenuItem(
                      child: Text('A'),
                      value: 1,
                  ),
                  DropdownMenuItem(
                      child: Text('B'),
                      value: 2,
                  ),
                  DropdownMenuItem(
                      child: Text('C'),
                      value: 3,
                  )
                ],
                onChanged: (newValue){
                  setState((){
                    selectedValue = newValue as int;
                  });
                }
            )
          ],
        ),
      ),
    );
  }