Flutter 悬浮控件

父布局嵌套Stack形成两个组件样式

_buildBody() {
    return Stack(
      children: [_buildList(), _buildCid()],
    );
  }

第一个不用讲了。。第二个是我们今天的重点

_buildCid() {
    return Positioned(
        left: _offset.dx,
        top: _offset.dy,
        child: GestureDetector(
          //滑动中，实时更新位置
          onPanUpdate: (detail) {
            setState(() {
              _offset = Offset(
                  _offset.dx + detail.delta.dx, _offset.dy + detail.delta.dy);
            });
          },
          //滑动结束 计算最后位置
          onPanEnd: (detail) {
            var margin = 5.0;
            //得到屏幕宽度 根据宽度吸到边上
            var screenWidth = MediaQuery.of(context).size.width;
            var screenHeight = MediaQuery.of(context).size.height;
            //得到当前控件宽
            var weightWidgth = _cidGlobalKey.currentContext.size.width;
            var weightHeight = _cidGlobalKey.currentContext.size.height;
            //得到 当前偏移量
            var offsetDx = _offset.dx;
            var offsetDy = _offset.dy;
            //右边吸边
            if (offsetDx >= screenWidth / 2) {
              offsetDx = screenWidth - weightWidgth - margin;
            } else {
              //左边吸边
              offsetDx = margin;
            }

            if (offsetDy <= 0) {
              offsetDy = margin;
            }
            //获取状态栏高度：
            final double statusBarHeight = MediaQuery.of(context).padding.top;
            //计算y轴的偏移量
            var maxHeight = screenHeight -
                weightHeight -
                kBottomNavigationBarHeight -
                kToolbarHeight -
                margin -
                statusBarHeight;
            if (offsetDy > maxHeight) {
              offsetDy = maxHeight;
            }

            setState(() {
              _offset = Offset(offsetDx, offsetDy);
            });
          },
          child: _cid.length > 0
              ? Chip(
                  key: _cidGlobalKey,
                  label: Text(
                    _cid,
                    style: TextStyle(color: Colors.white),
                  ),
                  backgroundColor: _colorPrimary,
                  onDeleted: () {
                    setState(() {
                      _cid = "";
                    });
                  },
                )
              : Container(),
        ));
  }

String _cid = "搞笑";

  // 当前页数//设定Widget的偏移量
  Offset _offset = Offset(20, 20);
  final GlobalKey _cidGlobalKey = GlobalKey();

效果可以参照。头像表情包app  点金详情后再点击最下面的分

目前还没上架先贴一个图吧

如果你的页面刚好包含FloatActionButton。。也需要处理一下

//得到FloatActionButton控件宽
            var floatActionButtonWeightWidgth =
                _floatActionButtonGlobalKey.currentContext.size.width + 20;
            var floatActionButtonWeightHeight =
                _floatActionButtonGlobalKey.currentContext.size.height + 20;
            //y超过对x做限制 x超过对y做限制

            //x和y分别都在FloatActionButton上面
            if (offsetDy > maxHeight - floatActionButtonWeightHeight &&
                offsetDx > maxWidth - floatActionButtonWeightWidgth) {
              offsetDx = maxWidth;
              offsetDy = maxHeight - floatActionButtonWeightHeight;
            }