How to handle user input in Flutter?

Flutter user input handling:\n\n**Text input:**\n\nTextField(\n controller: _controller,\n decoration: InputDecoration(\n labelText: 'Enter text',\n border: OutlineInputBorder()\n ),\n onChanged: (value) => print(value)\n)\n\n\n**Form validation:**\n\nForm(\n key: _formKey,\n child: TextFormField(\n validator: (value) {\n if (value?.isEmpty ?? true) {\n return 'Please enter text';\n }\n return null;\n }\n )\n)\n\n\n**Gesture detection:**\n\nGestureDetector(\n onTap: () => print('Tapped'),\n onLongPress: () => print('Long pressed'),\n child: Container(...)\n)\n\n\n**Button handling:**\n• ElevatedButton, TextButton, IconButton\n• onPressed callback\n• Disabled state when onPressed is null