flutter numberpicker

引入以来后直接这样写代码就好了！当成一个widget使用：

Column(
  mainAxisAlignment: MainAxisAlignment.center,
  children: <Widget>[
    NumberPicker.integer(
        initialValue: _currentValue,
        minValue: 0,
        maxValue: 100,
        onChanged: (newValue) =>
            setState(() => _currentValue = newValue)),
    Text("Current number: $_currentValue"),
  ],
),