UI中未显示DropDown列表中的选择

Question

当我尝试更改下拉列表中的值时，它并没有在那一刻更改它的值，但是当我返回并再次打开对话框时，该更改将反映在过去两天的卡住中，请帮帮我。我检查了onChanged（）是否正确调用，但是

value: currentMonth

在更改我关闭对话框并再次打开它时已调用的值后未调用。请帮帮我

下面是下拉代码

  void _filterDialog() {
    showDialog(
        context: context,
        builder: (BuildContext context) {
          return Dialog(
            child: Container(
              width: 300,
              height: 250,
              child: Column(
                children: <Widget>[
                  new Container(
                  child:   new DropdownButtonHideUnderline(
                    child: DropdownButton<String>(
                      value: currentMonth,
                      onChanged: (String newValue) {
                        setState(() {
                          currentMonth = newValue;
                          print(currentMonth);
                        });
                      },
                      items: <String>['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December']
                          .map<DropdownMenuItem<String>>((String value) {
                        return DropdownMenuItem<String>(
                          value: value,
                          child: Text(value),
                        );
                      }).toList(),
                    ),),
              )

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

在这里，我将currentMonth初始化为全局变量

 String currentMonth = "";

我正在initState（）中的currentMonth中填充值

@override
  void initState() {
    super.initState();
    if (currentYear.month == 1) {
      currentMonth = "January";
    } else if (currentYear.month == 2) {
      currentMonth = "February";
    } else if (currentYear.month == 3) {
      currentMonth = "March";
    } else if (currentYear.month == 4) {
      currentMonth = "April";
    } else if (currentYear.month == 5) {
      currentMonth = "May";
    } else if (currentYear.month == 6) {
      currentMonth = "June";
    } else if (currentYear.month == 7) {
      currentMonth = "July";
    } else if (currentYear.month == 8) {
      currentMonth = "August";
    } else if (currentYear.month == 9) {
      currentMonth = "September";
    } else if (currentYear.month == 10) {
      currentMonth = "October";
    } else if (currentYear.month == 11) {
      currentMonth = "November";
    } else if (currentYear.month == 12) {
      currentMonth = "December";
    }
  }