所需内容的最小示例：
class MyHomePage extends StatefulWidget { @override MyHomePageState createState() { return new MyHomePageState(); }}class MyHomePageState extends State<MyHomePage> { final _text = TextEditingController(); bool _validate = false; @override void dispose() { _text.dispose(); super.dispose(); } @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text('TextField Demo'), ), body: Center( child: Column( mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[ Text('Error Showed if Field is Empty on Submit button Pressed'), TextField( controller: _text, decoration: InputDecoration( labelText: 'Enter the Value', errorText: _validate ? 'Value Can't Be Empty' : null, ), ), RaisedButton( onPressed: () { setState(() { _text.text.isEmpty ? _validate = true : _validate = false; }); }, child: Text('Submit'), textColor: Colors.white, color: Colors.blueAccent, ) ], ), ), ); }}
