Javascript 无法读取属性';帆布';未定义的
我正在尝试使用chartsjs制作饼图。我遵循了chartjs文档中的步骤,包括了chart.js和canvas元素。我添加了创建图表的脚本,如chartjs文档中提供的示例。我得到以下错误: 未捕获的TypeError:无法读取未定义的属性“canvas” 有人知道如何解决这个问题吗?我做错了什么? 先走一步 代码如下:Javascript 无法读取属性';帆布';未定义的,javascript,jquery,canvas,charts,undefined,Javascript,Jquery,Canvas,Charts,Undefined,我正在尝试使用chartsjs制作饼图。我遵循了chartjs文档中的步骤,包括了chart.js和canvas元素。我添加了创建图表的脚本,如chartjs文档中提供的示例。我得到以下错误: 未捕获的TypeError:无法读取未定义的属性“canvas” 有人知道如何解决这个问题吗?我做错了什么? 先走一步 代码如下: <!DOCTYPE html> <html> <head> <script type="text/javas
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript" src="<?php echo base_url(); ?>media/js/chart.js"></script>
<script type="text/javascript" src="<?php echo base_url(); ?>media/js/jquery.js"></script>
</head>
<canvas id="myChart" width="400" height="400"></canvas>
<script type="text/javascript">
$(function() {
options = {
//Boolean - Show a backdrop to the scale label
scaleShowLabelBackdrop: true,
//String - The colour of the label backdrop
scaleBackdropColor: "rgba(255,255,255,0.75)",
// Boolean - Whether the scale should begin at zero
scaleBeginAtZero: true,
//Number - The backdrop padding above & below the label in pixels
scaleBackdropPaddingY: 2,
//Number - The backdrop padding to the side of the label in pixels
scaleBackdropPaddingX: 2,
//Boolean - Show line for each value in the scale
scaleShowLine: true,
//Boolean - Stroke a line around each segment in the chart
segmentShowStroke: true,
//String - The colour of the stroke on each segement.
segmentStrokeColor: "#fff",
//Number - The width of the stroke value in pixels
segmentStrokeWidth: 2,
//Number - Amount of animation steps
animationSteps: 100,
//String - Animation easing effect.
animationEasing: "easeOutBounce",
//Boolean - Whether to animate the rotation of the chart
animateRotate: true,
//Boolean - Whether to animate scaling the chart from the centre
animateScale: false,
//String - A legend template
legendTemplate: "<ul class=\"<%=name.toLowerCase()%>-legend\"><% for (var i=0; i<segments.length; i++){%><li><span style=\"background-color:<%=segments[i].fillColor%>\"></span><%if(segments[i].label){%><%=segments[i].label%><%}%></li><%}%></ul>"
};
data = [
{
value: 300,
color: "#F7464A",
highlight: "#FF5A5E",
label: "Red"
},
{
value: 50,
color: "#46BFBD",
highlight: "#5AD3D1",
label: "Green"
},
{
value: 100,
color: "#FDB45C",
highlight: "#FFC870",
label: "Yellow"
}
];
ctx = $("#myChart").get(0).getContext("2d");
myNewChart = new Chart(ctx[0]).Pie(data, options);
});
</script>
</html>
问题在于这一行:
myNewChart = new Chart(ctx[0]).Pie(data, options);
特别是在ctx[0]
中。当您在此处定义ctx
时:
ctx = $("#myChart").get(0).getContext("2d");
ctx
是一个名为CanvasRenderingContext2D
的对象,它具有属性。您正试图将其视为一个数组,但它不是<因此,code>ctx[0]
未定义。因此,正如您所发现的,解决方案实际上很简单
将ctx[0]
更改为ctx
,您就有了漂亮的动画饼图
ctx = $("#myChart").get(0).getContext("2d");
myNewChart = new Chart(ctx).Pie(data, options);
我的解决方案有点不同,因为我希望动态更改图表(在我的应用程序中,它使用滑块移动),但避免可怕的闪烁 在标准实例化之后,我在拖动滑块时进行更新,如下所示:
var chartData = getChartData();
for(var i=0; i<chartData.length; i++)
{
barChart.datasets[0].bars[i].value = chartData[i];
}
barChart.update();
var chartData=getChartData();
对于(var i=0;我发现了它;显然它只是ctx而不是ctx[0]图表(ctx)。Pie(数据,选项);非常感谢。我觉得很愚蠢,这太明显了,我没有看到它。我感到羞耻。这种混乱源于chartjs文档。饼图的示例使用了新图表(ctx[0])。Pie(数据,选项);
if(barChart) {
barChart.clear();
barChart.destroy();
}
chartDataObject = getChartData();
var chartData = {
labels: getChartLabels(),
datasets: [
{
label: "label",
fillColor: "rgba(151,187,205,0.5)",
strokeColor: "rgba(151,187,205,0.8)",
highlightFill: "rgba(151,187,205,0.75)",
highlightStroke: "rgba(151,187,205,1)",
data: chartDataObject
}
]
};
var chartContext = $("#visualizeEfficacyBar").get(0).getContext("2d");
barChart = new Chart(chartContext).Bar(chartData, { tooltipTemplate: "<%if (label){%><%=label%>: <%}%><%= value %>", responsive : true , animate : false, animationSteps : 1 });