FlutterDropdownButton不允許我從下拉串列中選擇不同的值

這是我的代碼

DropdownButton<int>(
                value: map['completedVersion'].toInt(), //selected
                elevation: 16,
                style: TextStyle(color: Theme.of(context).accentColor),
                underline: Container(
                  height: 2,
                  color: Colors.blueAccent,
                ),
                onChanged: (int? newValue) {
                  versionInput.text = newValue.toString();
                  },
                items: [for (var i = map['completedVersion'].toInt() as int; i <= map['requiredVersion']; i  ) i]
                    .map<DropdownMenuItem<int>>((int value) {
                  return DropdownMenuItem<int>(
                    value: value,
                    child: Text(value.toString()),
                  );
                }).toList(),
              )

類級別宣告

  TextEditingController versionInput = TextEditingController();

  @override
  void initState() {
    versionInput.text = map['completedVersion'].toString(); //set the initial value of text field
    super.initState();
  }

這是行為

它不允許我選擇任何其他值（例如：4、5、6）。我確實看到當我輸入斷點時他的 onChanged() 方法被擊中。但我不確定為什么選擇會回到原始值。

uj5u.com熱心網友回復：

文本編輯值

class Example extends StatelessWidget {
  Example({Key? key}) : super(key: key);

  TextEditingController versionInput = TextEditingController(text: "2");

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        ValueListenableBuilder(
          valueListenable: versionInput,
          builder: (BuildContext context, TextEditingValue selectedValue, Widget? child) {
            return DropdownButton<int>(
              value: int.parse(selectedValue.text),
              elevation: 16,
              style: TextStyle(color: Theme.of(context).accentColor),
              underline: Container(
                height: 2,
                color: Colors.blueAccent,
              ),
              onChanged: (value) {},
              items: [for (var i = 0 as int; i <= 6; i  ) i].map<DropdownMenuItem<int>>((int value) {
                return DropdownMenuItem<int>(
                  value: value,
                  child: Text(value.toString()),
                  onTap: () {
                    versionInput.text = value.toString();
                  },
                );
              }).toList(),
            );
          },
        ),
      ],
    );
  }
}

如果你真的使用沒有文本欄位的TextEditingController并且不需要它，你可以直接在ValueNotifier中使用它。

值通知器

class Example extends StatelessWidget {
  Example({Key? key}) : super(key: key);

  ValueNotifier<int> versionInput = ValueNotifier<int>(2); // initialValue

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        ValueListenableBuilder(
          valueListenable: versionInput,
          builder: (BuildContext context, int selectedValue, Widget? child) {
            return DropdownButton<int>(
              value: selectedValue,
              elevation: 16,
              style: TextStyle(color: Theme.of(context).accentColor),
              underline: Container(
                height: 2,
                color: Colors.blueAccent,
              ),
              onChanged: (value) {},
              items: [for (var i = 0 as int; i <= 6; i  ) i].map<DropdownMenuItem<int>>((int value) {
                return DropdownMenuItem<int>(
                  value: value,
                  child: Text(value.toString()),
                  onTap: () {
                    versionInput.value = value;
                  },
                );
              }).toList(),
            );
          },
        ),
      ],
    );
  }
}

uj5u.com熱心網友回復：

你必須改變兩件事：

1- 值：map['completedVersion'].toInt()，==> 值：versionInput.text，

2-

onChanged: (newValue) {                     
    setState(() {
      versionInput.text = newValue.toString();
    });
},

uj5u.com熱心網友回復：

這應該作業：

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        ValueListenableBuilder(
          valueListenable: versionInput,
          builder: (BuildContext context, TextEditingValue selectedValue, Widget? child) {
            return DropdownButton<int>(
            hint: Text(
            int.parse(selectedValue.text) ?? '3'
            ),
              elevation: 16,
              style: TextStyle(color: Theme.of(context).accentColor),
              underline: Container(
                height: 2,
                color: Colors.blueAccent,
              ),
              onChanged: (int? newValue) {
    if(newValue != null){
    setState(()=>   versionInput.text = newValue.toString());
    }
       },
              items: [for (var i = 0; i <= 6; i  ) i].map<DropdownMenuItem<int>>((int value) {
                return DropdownMenuItem<int>(
                  value: value,
                  child: Text(value.toString()),
                  onTap: () {
                    versionInput.text = value.toString();
                  },
                );
              }).toList(),
            );
          },
        ),
      ],
    );
  }
}

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