Flutter中如何连续获取TextField的文本是否为空

It can be done without any temporary variable using ValueListenableBuilder

在一些研究发现

1. controller.text本身不是listenable
2. TextEditingController扩展到ValueNotifier<TextEditingValue>，即您可以使用material 包中的ValueListenableBuilder来收听文本更改.

代码:

class _MyWidgetState extends State<MyWidget> {
  late TextEditingController textEditingController;
  @override
  void initState() {
    textEditingController = TextEditingController();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          children: [
            TextField(
              controller: textEditingController,
            ),
            ValueListenableBuilder<TextEditingValue>(
              valueListenable: textEditingController,
              builder: (context, value, child) {
                return ElevatedButton(
                  onPressed: value.text.isNotEmpty ? () {} : null,
                  child: const Text('I am disabled when text is empty'),
                );
              },
            ),
          ],
        ),
      ),
    );
  }
}

不带文本:

带文本: