GestureDetector ,Draggable,DragTarget

import 'package:flutter/material.dart';
import 'package:flutter/painting.dart';

class WidgetGesture extends StatefulWidget {
  @override
  _WidgetGestureState createState() => _WidgetGestureState();
}

class _WidgetGestureState extends State<WidgetGesture> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: SingleChildScrollView(
        child: Column(
          children: [
            _buildGestureDetector(),
            Divider(),
            _buildDraggable(),
            Divider(),
            _buildDragTarget(),
          ],
        ),
      ),
    );
  }
}

Draggable<int> _buildDraggable() {
  return Draggable(
    child: Column(
      children: [
        Icon(
          Icons.palette,
          color: Colors.deepOrange,
          size: 48.0,
        ),
        Text('Drag me below to change color'),
      ],
    ),
    childWhenDragging: Icon(
      Icons.palette,
      color: Colors.grey,
      size: 48.0,
    ),
    feedback: Icon(
      Icons.brush,
      color: Colors.deepOrange,
      size: 80.0,
    ),
    data: Colors.deepOrange.value,
  );
}

DragTarget<int> _buildDragTarget() {
  Color _paintedColor;

  return DragTarget<int>(
    onAccept: (colorValue) {
      _paintedColor = Color(colorValue);
    },
    builder: (BuildContext context, List<dynamic> acceptedValue,
            List<dynamic> rejectedValue) =>
        acceptedValue.isEmpty
            ? Text(
                'Drag To and see color change',
                style: TextStyle(color: _paintedColor),
              )
            : Text(
                'Painting Color :$acceptedValue',
                style: TextStyle(
                    color: Color(acceptedValue[0]),
                    fontWeight: FontWeight.bold),
              ),
  );
}

class _buildGestureDetector extends StatefulWidget {
  @override
  __buildGestureDetectorState createState() => __buildGestureDetectorState();
}

class __buildGestureDetectorState extends State<_buildGestureDetector> {
  String gestureDetected = '';

  void _displayGesture(String g) {
    setState(() {
      gestureDetected = g;
    });
  }

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: () {
        _displayGesture('onTap');
      },
      onDoubleTap: () {
        _displayGesture('onDoubleTap');
      },
      onLongPress: () {
        _displayGesture('onLongPress');
      },
      onPanUpdate: (DragUpdateDetails dragUpdateDetails) {
        _displayGesture(dragUpdateDetails.toString());
      },
      child: Container(
        color: Colors.green.shade100,
        width: double.infinity,
        padding: EdgeInsets.all(24.0),
        child: Column(
          children: [
            Icon(
              Icons.alarm,
              size: 98,
            ),
            SizedBox(
              height: 15,
            ),
            Text(
              gestureDetected,
              style: TextStyle(
                fontSize: 40,
              ),
            ),
          ],
        ),
      ),
    );
  }
}