uCharts在手机模拟器中无法正常显示，请问是什么原因

onLoad() {  
            _self = this;  
            this.cWidth = uni.upx2px(750);  
            this.cHeight = uni.upx2px(500);  
            this.loadChartData();  
},  
methods: {  
      loadChartData() {  
                let url = "...";  
                console.log("服务器地址: " + url);  
                let params = null;  
                uni.request({  
                    url: url,  
                    method: 'POST',  
                    data: params,  
                    dataType: 'json',  
                    success: function(res) {  
                        console.log(res.data.data);  
                        let lineData = {  
                            categories: [],  
                            series: []  
                        };  
                        lineData.categories = (res.data.data)["categories"];  
                        lineData.series = (res.data.data)["series"];  
                        _self.showLineChart('canvasLine', lineData);  
                    },  
                    fail: function(res) {  
                        this.tips = "网络错误";  
                    }  
                });  
           },  

      showLineChart(canvasId, chartData) {  
                console.log("显示图表: canvasId=" + canvasId + ", chartData=" + chartData);  
                canvasLine = new uCharts({  
                    $this: _self,  
                    canvasId: canvasId,  
                    type: 'line',  
                    fontSize: 11,  
                    legend: {  
                        show: true,  
                        padding: 5,  
                        lineHeight: 11,  
                        margin: 0  
                    },  
                    dataLabel: false,  
                    dataPointShape: true,  
                    background: '#FFFFFF',  
                    pixelRatio: _self.pixelRatio,  
                    categories: chartData.categories,  
                    series: chartData.series,  
                    animation: true,  
                    xAxis: {  
                        type: 'grid',  
                        gridColor: '#CCCCCC',  
                        gridType: 'dash',  
                        dashLength: 8,  
                        scrollShow: true  
                    },  
                    yAxis: {  
                        gridType: 'dash',  
                        gridColor: '#CCCCCC',  
                        dashLength: 8  
                        // ,splitNumber: 5,  
                        // min: 0,  
                        // max: 20,  
                        // format: (val) => {  
                        //  return val.toFixed(0) + '点'  
                        // }  
                    },  
                    width: _self.cWidth * _self.pixelRatio,  
                    height: _self.cHeight * _self.pixelRatio,  
                    extra: {  
                        line: {  
                            type: 'straight'  
                        }  
                    }  
                });  
            }  

}