Flutter 拖拽控件Draggable看这一篇就够了

Draggable(
  child: Container(
    height: 100,width: 100,alignment: Alignment.center,decoration: BoxDecoration(
      color: Colors.red,borderRadius: BorderRadius.circular(10)
    ),child: Text('孟',style: TextStyle(color: Colors.white,fontSize: 18),),feedback: Container(
    height: 100,decoration: BoxDecoration(
        color: Colors.blue,)

Draggable(
  childWhenDragging: Container(
    height: 100,decoration: BoxDecoration(
        color: Colors.grey,borderRadius: BorderRadius.circular(10)),child: Text(
      '孟',...
)

Draggable(
  axis: Axis.vertical,...
)

Draggable(
  onDragStarted: (){
    print('onDragStarted');
  },onDragEnd: (DraggableDetails details){
    print('onDragEnd:$details');
  },onDraggableCanceled: (Velocity velocity,Offset offset){
    print('onDraggableCanceled velocity:$velocity,offset:$offset');
  },onDragCompleted: (){
    print('onDragCompleted');
  },...
)

• onDragStarted：开始拖动时回调。
• onDragEnd：拖动结束时回调。
• onDraggableCanceled：未拖动到DragTarget控件上时回调。
• onDragCompleted：拖动到DragTarget控件上时回调。

DragTarget(
  builder: (BuildContext context,List<dynamic> candidateData,List<dynamic> rejectedData) {
      ...
  }
)

• onWillAccept：拖到该控件上时调用，需要返回true或者false，返回true，松手后会回调onAccept，否则回调onLeave。
• onAccept：onWillAccept返回true时，用户松手后调用。
• onLeave：onWillAccept返回false时，用户松手后调用。

var _dragData;

@override
Widget build(BuildContext context) {
  return Center(
    child: Column(
      children: <Widget>[
        _buildDraggable(),SizedBox(
          height: 200,DragTarget<Color>(
          builder: (BuildContext context,List<Color> candidateData,List<dynamic> rejectedData) {
            print('candidateData:$candidateData,rejectedData:$rejectedData');
            return _dragData == null
                ? Container(
                    height: 100,decoration: BoxDecoration(
                        borderRadius: BorderRadius.circular(10),border: Border.all(color: Colors.red)),)
                : Container(
                    height: 100,decoration: BoxDecoration(
                        color: Colors.red,child: Text(
                      '孟',);
          },onWillAccept: (Color color) {
            print('onWillAccept:$color');
            return true;
          },onAccept: (Color color) {
            setState(() {
              _dragData = color;
            });
            print('onAccept:$color');
          },onLeave: (Color color) {
            print('onLeave:$color');
          },],);
}

_buildDraggable() {
  return Draggable(
    data: Color(0x000000FF),child: Container(
      height: 100,decoration: BoxDecoration(
          color: Colors.red,child: Text(
        '孟',feedback: Container(
      height: 100,decoration: BoxDecoration(
          color: Colors.blue,child: DefaultTextStyle.merge(
        style: TextStyle(color: Colors.white,child: Text(
          '孟',);
}