尝试创建动态文本输入构件时"Invalid constant value"

Question

我正在尝试创建一个新的TextInput小部件来自定义TextFormField，但我无法自定义labelText。我需要为我的TextFormField发送构造函数labelText并显示此字符串。

class TextInput extends StatelessWidget {

final TextEditingController textControler;
final String textLabelHint;
const TextInput({Key? key, required this.textControler,required this.textLabelHint}) : super(key: key);
@override
Widget build(BuildContext context) {
return Padding(
padding: const EdgeInsets.only(top: 10.0),
child: TextFormField(
controller: textControler,
decoration: const InputDecoration(
border: OutlineInputBorder(),
labelText: textLabelHint, 
),
),
);
}
}

但我有问题：

labelText: textLabelHint, //Invalid constant value. 

Answer 1

您需要从decoration: const InputDecoration(...)中删除const，因为textLabelHint不是const值：

class TextInput extends StatelessWidget {
final TextEditingController textControler;
final String textLabelHint;
const TextInput(
{Key? key, required this.textControler, required this.textLabelHint})
: super(key: key);
@override
Widget build(BuildContext context) {
return Padding(
padding: const EdgeInsets.only(top: 10.0),
child: TextFormField(
controller: textControler,
decoration: InputDecoration(
border: OutlineInputBorder(),
labelText: textLabelHint,
),
),
);
}
}

Answer 2

之所以出现此错误，是因为textLabelHint是一个最终类属性(而非常量(，它可能会根据构造函数值进行更改。但是，尝试传递此值的位置是InputDecoration，您已将其标记为const。因此，错误表明。

要解决此问题，请删除InputDecoration:之前的const关键字

class TextInput extends StatelessWidget {
final TextEditingController textControler;
final String textLabelHint;
const TextInput({Key? key, required this.textControler,required this.textLabelHint}) : super(key: key);
@override
Widget build(BuildContext context) {
return Padding(
padding: const EdgeInsets.only(top: 10.0),
child: TextFormField(
controller: textControler,
decoration: InputDecoration( // <-- Notice the removed const
border: OutlineInputBorder(),
labelText: textLabelHint, 
),
),
);

Answer 3

试试这个：

class TextInput extends StatelessWidget {
final TextEditingController textControler;
final String textLabelHint;
const TextInput(
{Key? key, required this.textControler, required this.textLabelHint})
: super(key: key);
@override
Widget build(BuildContext context) {
return Padding(
padding: const EdgeInsets.only(top: 10.0),
child: TextFormField(
controller: textControler,
decoration: InputDecoration(
border: const OutlineInputBorder(),
labelText: textLabelHint,
),
),
);
}
}