饼状图自定义了高亮显示和点击时候高亮显示及自定义操作，

产生问题：

1.刚加载时候的默认高亮不起作用

2.点击空白区域，高亮消失

解决方法：

直接设置不起作用，将设置加在$nextTick里，问题解决

代码示例：

    setPieOption(data, success) {

        this.ec2.option.series[0].data = data

        this.$nextTick(()=>{

          this.$refs.echartsUni.$curChart.dispatchAction({

            type: 'highlight',

            seriesIndex: 0,

            dataIndex: 0

          })

          if (success) {

            this.clickPieChart(success)

          }

        })

      },

      clickPieChart (success) {

        let _this = this

        _this.$refs.echartsUni.$curChart.off('click')

        _this.$refs.echartsUni.$curChart.on('click', function(params) {

          _this.$refs.echartsUni.$curChart.dispatchAction({

            type: 'downplay',

            seriesIndex: 0,

            dataIndex: _this.dataIndex

          })

          _this.$refs.echartsUni.$curChart.dispatchAction({

            type: 'highlight',

            seriesIndex: 0,

            dataIndex: params.dataIndex

          })

          _this.dataIndex = params.dataIndex

          success(params.dataIndex)

        })

      },