Flutter仿照苹果相册长按下拉滚动多选中

最近朋友想让我实现一个仿苹果相册长按下拉选中的效果,奈何度娘不给力,找不到任何的有关文章,索性就自己来实现吧。希望以后有此需求的朋友能借鉴借鉴自己的文章,这样也不枉自己花些笔墨为大家来介绍实现的思路和方法。

实现效果:(长按下拉选中后续选项)


2222.gif

首先,我们先来实现最基本的效果,单击选中,再单击,取消选中

import 'package:flutter/material.dart';

class AlbumDemo extends StatefulWidget {
  const AlbumDemo({Key? key}) : super(key: key);

  @override
  State createState() => _AlbumDemoState();
}

class _AlbumDemoState extends State {


  List selects = [];

  @override
  void initState() {
    super.initState();
    for(int i = 0; i < 400 ; i++){
      selects.add(0);
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('AlbumDemo'),),
      body: ListView.builder(itemBuilder: (BuildContext context,int index){
        return GestureDetector(
            onTap: (){
              selects[index] = ((selects[index]??0)==0)?1:0;
              setState(() {

              });
            },
            child: Container(
              color: Colors.white,
              child: Column(
                children: [
                  Container(
                      height: 80,
                      child: Row(
                        children: [
                          Icon( ((selects[index]??0) ==1)?Icons.check_box:Icons.check_box_outline_blank,),
                          SizedBox(width: 50,),
                          Text('$index'),
                        ],
                      )
                  ),
                  Container(
                    height: 0.5,
                    color: Colors.lightBlue,
                  )
                ],
              ),
            )
        );
      },itemCount: 400,),
    );
  }
}

接下来利用手势来判别滑动轨迹,并且为listview添加controller控制滑动


import 'package:flutter/material.dart';

enum PullDirection {
  down,
  up,
}

class AlbumDemo extends StatefulWidget {
  const AlbumDemo({Key? key}) : super(key: key);

  @override
  State createState() => _AlbumDemoState();
}

class _AlbumDemoState extends State {

  List selects = [];//选中的暂存数组

  ScrollController _controller = ScrollController();

  double origin_offset = 0;//原始的标记位置,用来判别是上拉还是下滑

  bool endDrap = false;//结束滑动的标志

  bool isPullingUp = false;//是否正在上滑中

  bool isPullingDown = false;//是否正在下滑中

  bool isAnimationing = false;//是否处于自动滚动中

  final GlobalKey _globalKey = GlobalKey();//用来获取当前的listview

  Offset saveOffset = Offset(0, 0);

  PullDirection direction = PullDirection.down;//滑动方向

  @override
  void initState() {
    super.initState();
    for(int i = 0; i < 400 ; i++){
      selects.add(0);
    }
  }


  runloopScroll(bool down){

    print("isPullingDown = $isPullingDown");
    if(down){
      origin_offset+=80;
    }else{
      origin_offset-=80;
      if(origin_offset<0){
        origin_offset = 0;
      }
    }
    Future.delayed(Duration(milliseconds: 200),(){
      if(down){
        _controller.animateTo(origin_offset, duration: Duration(milliseconds: 200),curve:Curves.linear );
      }else{
        _controller.animateTo(origin_offset, duration: Duration(milliseconds: 200),curve:Curves.linear );
      }
    }).then((value){
      RenderBox box = _globalKey.currentContext?.findRenderObject() as RenderBox;
      var innerLocation =  box.globalToLocal(saveOffset);
      updateSelectionStatus(Offset(innerLocation.dx, innerLocation.dy+ (down?80:-80)),isSelected: direction==PullDirection.down);


      if(endDrap == true){
      }else{
        if(down){//下滑中
          if(isPullingDown) {
            runloopScroll(true);
          }
        }else{
          if(isPullingUp){
            runloopScroll(false);
          }
        }
      }

    });
  }


  updateSelectionStatus(Offset offset,{bool isSelected = true}){

    int index =   (_controller.offset.toInt() +   offset.dy.toInt()) ~/ 80 ;
    // print('滑动经过的index=$index');

    selects[index] = isSelected?1:0;
    setState(() {

    });


  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('AlbumDemo'),),
      body: GestureDetector(
        onLongPress: (){
          print("长按开始");
          endDrap = false;
          origin_offset = _controller.offset;
        },
        onLongPressEnd: (LongPressEndDetails details){
          print("长按结束");
          endDrap = true;
          isAnimationing = false;
        },
        onLongPressMoveUpdate:(LongPressMoveUpdateDetails details){
          if(saveOffset.dy < details.globalPosition.dy){
            //下滑
            direction = PullDirection.down;
          }else{
            //上滑
            direction = PullDirection.up;
          }
          saveOffset = details.globalPosition;
          RenderBox box = _globalKey.currentContext?.findRenderObject() as RenderBox;
          var innerLocation =  box.globalToLocal(saveOffset);
          updateSelectionStatus(innerLocation,isSelected: direction==PullDirection.down);
          if(details.globalPosition.dy>=810){//下面的边缘临界点,目前写死(这里应该是导航栏与定点的距离)
            if(isPullingUp){
              isPullingUp = false;
            }
            isPullingDown = true;
            if(isAnimationing){

            }else{
              runloopScroll(true);
              isAnimationing = true;
            }
          }else if(details.globalPosition.dy<=120){//上面的临界点,这里应该是底部离定点的距离
            if(isPullingDown){
              isPullingDown = false;
              isAnimationing = false;
            }
            isPullingUp = true;
            if(isAnimationing){

            }else{
              runloopScroll(false);
              isAnimationing = true;
            }
          }else{
            if(isPullingDown){
              isPullingDown = false;
              isAnimationing = false;
            }
            if(isPullingUp){
              isPullingUp = false;
            }
          }
        },
        child: ListView.builder(key: _globalKey,controller: _controller,itemBuilder: (BuildContext context,int index){
          return GestureDetector(
              onTap: (){
                selects[index] = ((selects[index]??0)==0)?1:0;
                setState(() {

                });
              },
              child: Container(
                color: Colors.white,
                child: Column(
                  children: [
                    Container(
                        height: 80,
                        child: Row(
                          children: [
                            Icon( ((selects[index]??0) ==1)?Icons.check_box:Icons.check_box_outline_blank,),
                            SizedBox(width: 50,),
                            Text('$index'),
                          ],
                        )
                    ),
                    Container(
                      height: 0.5,
                      color: Colors.lightBlue,
                    )
                  ],
                ),
              )
          );
        },itemCount: 400,),
      )
    );
  }
}



大功告成、楼主省略了讲解步骤,请见下回分解 哈哈

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