brush selected 无效echarts 折线配置项内容和展示

brush selected 不能正确保存所选择的数据 如果是柱状图是可以框选的

      option = {
    title: {
        text: '折线图堆叠'
    },
    tooltip: {
        trigger: 'axis'
    },
    legend: {
        data:['邮件营销','联盟广告','视频广告','直接访问','搜索引擎']
    },
    grid: {
        left: '3%',
        right: '4%',
        bottom: '3%',
        containLabel: true
    },
    toolbox: {
        feature: {
            saveAsImage: {}
        }
    },
    brush: {
          toolbox: ['rect', 'keep', 'clear'],
          brushStyle: {
            borderWidth: 3,
            color: 'rgba(0,0,0,0)',
            borderColor: '#E80B0B'
          },
          xAxisIndex: 'all',
          throttleType: 'debounce',
          throttleDelay: 1500

        },
    xAxis: {
        type: 'category',
        boundaryGap: false,
        data: ['周一','周二','周三','周四','周五','周六','周日']
    },
    yAxis: {
        type: 'value'
    },
    series: [
        {
            name:'邮件营销',
            type:'line',
            stack: '总量',
            data:[120, 132, 101, 134, 90, 230, 210]
        },
        {
            name:'联盟广告',
            type:'line',
            stack: '总量',
            data:[220, 182, 191, 234, 290, 330, 310]
        },
        {
            name:'视频广告',
            type:'line',
            stack: '总量',
            data:[150, 232, 201, 154, 190, 330, 410]
        },
        {
            name:'直接访问',
            type:'line',
            stack: '总量',
            data:[320, 332, 301, 334, 390, 330, 320]
        },
        {
            name:'搜索引擎',
            type:'line',
            stack: '总量',
            data:[820, 932, 901, 934, 1290, 1330, 1320]
        }
    ]
};
myChart.on('brushSelected', function (params) {
console.log(params)
    var brushComponent = params.batch[0];

    var sum = 0; // 统计选中项的数据值的和

    for (var sIdx = 0; sIdx < brushComponent.selected.length; sIdx++) {
        // 对于每个 series：
        var dataIndices = brushComponent.selected[sIdx].dataIndex;

        for (var i = 0; i < dataIndices.length; i++) {
            var dataIndex = dataIndices[i];
            sum += dataBySeries[sIdx][dataIndex];
        }
    }
    console.log(sum); // 为什么输出为 0 ？
});