Full pre:
class YourPage extends StatefulWidget { @override _YourPageState createState() => _YourPageState();}class _YourPageState extends State<YourPage> { double _maxHeight = 200, _minHeight = 44, _height = 44, _dividerHeight = 56, _offset = 19; int _maxLines = 1; static final Duration _fixDuration = Duration(milliseconds: 500); Duration _duration = _fixDuration; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(), body: Padding( padding: const EdgeInsets.all(20), child: SizedBox( height: _maxHeight, child: Column( children: <Widget>[ AnimatedContainer( duration: _duration, height: _height, child: TextField( decoration: InputDecoration(hintText: "Enter a message"), maxLines: _maxLines, ), ), Container( height: _dividerHeight, width: 200, child: Row( mainAxisAlignment: MainAxisAlignment.spaceAround, children: <Widget>[ IconButton(icon: Icon(Icons.arrow_downward),onPressed: () { if (_height <= _maxHeight - _offset - _dividerHeight) { setState(() { _duration = _fixDuration; _height += _offset; _maxLines++; }); }}, ), GestureDetector(child: Icon(Icons.drag_handle),onPanUpdate: (details) { setState(() { _height += details.delta.dy; _duration = Duration.zero; // prevent overflow if height is more/less than available space var maxLimit = _maxHeight - _dividerHeight; var minLimit = 44.0; if (_height > maxLimit) _height = maxLimit; else if (_height < minLimit) _height = minLimit; _maxLines = 100; });}, ), IconButton(icon: Icon(Icons.arrow_upward),onPressed: () { if (_height >= _minHeight + _offset) { setState(() { _duration = _fixDuration; _height -= _offset; }); }}, ), ], ), ) ], ), ), ), ); }}
