javascript - Chart.js 使用 X 轴时间动态更新图表

Question

我使用的是 Chart.js 版本 2.7.1，当温度数据出现时，我会动态更新折线图。

问题是这些线永远不会及时通过 x 轴的中间标记。每次我更新时，图表都会自动缩放 x 轴的右侧(最大时间)以使其更远，因此我的数据永远不会接近图表的右侧。我想要的是让这条线接近右侧，每次更新时，x 轴的 future 只有一小段时间。我怎样才能做到这一点？

这是我配置图表的方式:

var ctx = document.getElementById('tempChart').getContext('2d');
ctx.canvas.width = 320;
ctx.canvas.height = 240;

var chart = new Chart(ctx, {
  type: 'line',
  data: {
      labels: [],
      legend: {
         display: true
      },
      datasets: [{
          fill: false,
          data: [],
          label: 'Hot Temperature',
          backgroundColor: "#FF2D00",
          borderColor: "#FF2D00",
          type: 'line',
          pointRadius: 1,
          lineTension: 2,
          borderWidth: 2
      },
      {
          fill: false,
          data: [],
          label: 'Cold Temperature',
          backgroundColor: "#0027FF",
          borderColor: "#0027FF",
          type: 'line',
          pointRadius: 1,
          lineTension: 2,
          borderWidth: 2
      }]
  },
  options: {
    animation: false,
    responsive: true,
    scales: {
      xAxes: [{
          scaleLabel: {
            display: true,
            labelString: 'Time ( UTC )'
          },
          type: 'time',
          time: {
            tooltipFormat: "hh:mm:ss",
            displayFormats: {
              hour: 'MMM D, hh:mm:ss'
            }
          },
          ticks: {
                    maxRotation: 90,
                    minRotation: 90
          }
      }],
      yAxes: [{
        scaleLabel: {
          display: true,
          labelString: 'Temperature ( Celcius )'
        },
      }]
    }
  }
});

这是图表:

Answer 1

如您在以下代码片段中所见，还要感谢 Daniel W Strimpel对于创建初始代码段，您的问题在于hot 和cold temperature data。

{ x: new Date(2019, 0, 1, 14, 1, 19, 0), y: Math.random() * 0.5 + 35 },
{ x: new Date(2019, 0, 1, 14, 1, 20, 0), y: Math.random() * 0.5 + 35 },
{ x: new Date(2019, 0, 1, 14, 1, 21, 0), y: Math.random() * 0.5 + 35 },
{ x: new Date(2019, 0, 1, 14, 1, 22, 0), y: Math.random() * 0.5 + 35 },
{ x: new Date(2019, 0, 1, 14, 1, 23, 0), y: Math.random() * 0.5 + 35 },
{ x: new Date(2019, 0, 1, 14, 1, 24, 0), y: Math.random() * 0.5 + 35 },
{ x: new Date(2019, 0, 1, 14, 1, 25, 0), y: Math.random() * 0.5 + 35 },
{ x: new Date(2019, 0, 1, 14, 1, 26, 0) },
{ x: new Date(2019, 0, 1, 14, 1, 27, 0) },
{ x: new Date(2019, 0, 1, 14, 1, 28, 0) },
{ x: new Date(2019, 0, 1, 14, 1, 29, 0) },
{ x: new Date(2019, 0, 1, 14, 1, 30, 0) }

这两个数组最后都有 n 个条目缺少 y 坐标，包括 温度值。我通过删除冷热温度 data 的最后 5 个条目的 y 重新创建了您的场景。

图表 会将日期添加到x 轴，但不会添加温度 值，并且不会显示线条.

{x: new Data(2019, 0, 14, 1, 26, 0) }

该代码片段重新创建了您的场景，您可以运行它以了解问题并通过将 y 值添加到 getHotTempData 和 getColdTempData

var ctx = document.getElementById('tempChart').getContext('2d');
ctx.canvas.width = 320;
ctx.canvas.height = 240;

var chart = new Chart(ctx, {
  type: 'line',
  data: {
      labels: [],
      legend: {
         display: true
      },
      datasets: [{
          fill: false,
          data: getHotTempData(),
          label: 'Hot Temperature',
          backgroundColor: "#FF2D00",
          borderColor: "#FF2D00",
          type: 'line',
          pointRadius: 1,
          lineTension: 2,
          borderWidth: 2
      },
      {
          fill: false,
          data: getColdTempData(),
          label: 'Cold Temperature',
          backgroundColor: "#0027FF",
          borderColor: "#0027FF",
          type: 'line',
          pointRadius: 1,
          lineTension: 2,
          borderWidth: 2
      }]
  },
  options: {
    animation: false,
    responsive: true,
    scales: {
      xAxes: [{
          scaleLabel: {
            display: true,
            labelString: 'Time ( UTC )'
          },
          type: 'time',
          time: {
            tooltipFormat: "hh:mm:ss",
            displayFormats: {
              hour: 'MMM D, hh:mm:ss'
            }
          },
          ticks: {
                    maxRotation: 90,
                    minRotation: 90
          }
      }],
      yAxes: [{
        scaleLabel: {
          display: true,
          labelString: 'Temperature ( Celcius )'
        },
      }]
    }
  }
});

function getHotTempData() {
  return [
    { x: new Date(2019, 0, 1, 14, 1, 19, 0), y: Math.random() * 0.5 + 35 },
    { x: new Date(2019, 0, 1, 14, 1, 20, 0), y: Math.random() * 0.5 + 35 },
    { x: new Date(2019, 0, 1, 14, 1, 21, 0), y: Math.random() * 0.5 + 35 },
    { x: new Date(2019, 0, 1, 14, 1, 22, 0), y: Math.random() * 0.5 + 35 },
    { x: new Date(2019, 0, 1, 14, 1, 23, 0), y: Math.random() * 0.5 + 35 },
    { x: new Date(2019, 0, 1, 14, 1, 24, 0), y: Math.random() * 0.5 + 35 },
    { x: new Date(2019, 0, 1, 14, 1, 25, 0), y: Math.random() * 0.5 + 35 },
    { x: new Date(2019, 0, 1, 14, 1, 26, 0) },
    { x: new Date(2019, 0, 1, 14, 1, 27, 0) },
    { x: new Date(2019, 0, 1, 14, 1, 28, 0) },
    { x: new Date(2019, 0, 1, 14, 1, 29, 0) },
    { x: new Date(2019, 0, 1, 14, 1, 30, 0) }
  ];
}

function getColdTempData() {
  return [
    { x: new Date(2019, 0, 1, 14, 1, 19, 0), y: Math.random() * 0.5 + 23.5 },
    { x: new Date(2019, 0, 1, 14, 1, 20, 0), y: Math.random() * 0.5 + 23.5 },
    { x: new Date(2019, 0, 1, 14, 1, 21, 0), y: Math.random() * 0.5 + 23.5 },
    { x: new Date(2019, 0, 1, 14, 1, 22, 0), y: Math.random() * 0.5 + 23.5 },
    { x: new Date(2019, 0, 1, 14, 1, 23, 0), y: Math.random() * 0.5 + 23.5 },
    { x: new Date(2019, 0, 1, 14, 1, 24, 0), y: Math.random() * 0.5 + 23.5 },
    { x: new Date(2019, 0, 1, 14, 1, 25, 0), y: Math.random() * 0.5 + 23.5 },
    { x: new Date(2019, 0, 1, 14, 1, 26, 0) },
    { x: new Date(2019, 0, 1, 14, 1, 27, 0) },
    { x: new Date(2019, 0, 1, 14, 1, 28, 0) },
    { x: new Date(2019, 0, 1, 14, 1, 29, 0) },
    { x: new Date(2019, 0, 1, 14, 1, 30, 0) }
  ];
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.24.0/moment-with-locales.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.3/Chart.min.js"></script>
<canvas id="tempChart"></canvas>