flutter Draggable Widget拖拽控件

Draggable Widget

Draggable控件负责就是拖拽，父层使用了Draggable，它的子元素就是可以拖动的，子元素可以实容器，可以是图片。用起来非常的灵活。

参数说明：

• data: 是要传递的参数，在DragTarget里，会接受到这个参数。当然要在拖拽控件推拽到DragTarget的时候。
• child:在这里放置你要推拽的元素，可以是容器，也可以是图片和文字。
• feedback: 常用于设置推拽元素时的样子，在案例中当推拽的时候，我们把它的颜色透明度变成了50%。当然你还可以改变它的大小。
• onDraggableCanceled:是当松开时的相应事件，经常用来改变推拽时到达的位置，改变时用setState来进行。

  Draggable(
    data:widget.widgetColor,
    child: Container(
       100,
      height: 100,
      color:widget.widgetColor,
    ),
    feedback:Container(
       100.0,
      height: 100.0,
      color: widget.widgetColor.withOpacity(0.5),
    ),
    onDraggableCanceled: (Velocity velocity, Offset offset){
      setState(() {
        this.offset = offset;
      });
    },

  DragTarget Widget

  DragTarget是用来接收拖拽事件的控件，当把Draggable放到DragTarget里时，他会接收Draggable传递过来的值，然后用生成器改变组件状态。

  • onAccept:当推拽到控件里时触发，经常在这里得到传递过来的值。
  • builder: 构造器，里边进行修改child值。

DragTarget(onAccept: (Color color) {
  _draggableColor = color;
}, builder: (context, candidateData, rejectedData) {
  return Container(
     200.0,
    height: 200.0,
    color: _draggableColor,
  );
}),

demo

import 'package:flutter/material.dart';
import 'package:flutter_app/pages/SplashScreen.dart';

import 'ToolTipDemo.dart';
import 'draggable_demo.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.green,  //定义主题风格    primarySwatch
      ),
      home:  DraggableDemo(),
    );
  }

}

import 'package:flutter/material.dart';

import 'draggable_widget.dart';

class DraggableDemo extends StatefulWidget {
  @override
  _DraggableDemoState createState() => _DraggableDemoState();
}

class _DraggableDemoState extends State<DraggableDemo> {
  Color _draggableColor = Colors.grey;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Stack(
          children: <Widget>[
            DraggableWidget(
              offset: Offset(80.0, 80.0),
              widgetColor: Colors.tealAccent,
            ),
            DraggableWidget(
              offset: Offset(180.0, 80.0),
              widgetColor: Colors.redAccent,
            ),
            Center(
              child: DragTarget(onAccept: (Color color) {
                _draggableColor = color;
              }, builder: (context, candidateData, rejectedData) {
                return Container(
                   200.0,
                  height: 200.0,
                  color: _draggableColor,
                );
              }),
            )
          ],
        ));
  }
}

import 'package:flutter/material.dart';

class DraggableWidget extends StatefulWidget {
  final Offset offset;
  final Color widgetColor;
  const DraggableWidget({Key key, this.offset, this.widgetColor}):super(key:key);
  _DraggableWidgetState createState() => _DraggableWidgetState();
}

class _DraggableWidgetState extends State<DraggableWidget> {
  Offset offset = Offset(0.0,0.0);
  @override
  void initState() {
    super.initState();
    offset = widget.offset;
  }

  @override
  Widget build(BuildContext context) {
    return Positioned(
      left: offset.dx,
      top:offset.dy,
      child: Draggable(
        data:widget.widgetColor,
        child: Container(
           100,
          height: 100,
          color:widget.widgetColor,
        ),
        feedback:Container(
           100.0,
          height: 100.0,
          color: widget.widgetColor.withOpacity(0.5),
        ),
        onDraggableCanceled: (Velocity velocity, Offset offset){
          setState(() {
            this.offset = offset;
          });
        },
      ),
    );
  }
}

效果：