javascript - Chart.js v2 : How to make tooltips always appear on pie chart?

Question

我找到了similar questions在 Stack Overflow 上，但所有这些问题都在一两年前得到了解决。现在 Chart.js 已经出现在版本 2 中，并且许多文档发生了变化。有人可以帮我展示带有标签的饼图示例 - 或所有部分的工具提示都可见的饼图吗？

更新

感谢@potatopeelings，他的答案非常适合 Chart.js v2.1。

虽然我最初询问如何在饼图上永久显示工具提示，但我找到了更好的解决方案:将值显示为百分比标签!现在在 Chart.js v2.1 中启用了饼图。在图表选项中:

animation: {
  duration: 0,
  onComplete: function () {
    var self = this,
        chartInstance = this.chart,
        ctx = chartInstance.ctx;

    ctx.font = '18px Arial';
    ctx.textAlign = "center";
    ctx.fillStyle = "#ffffff";

    Chart.helpers.each(self.data.datasets.forEach(function (dataset, datasetIndex) {
        var meta = self.getDatasetMeta(datasetIndex),
            total = 0, //total values to compute fraction
            labelxy = [],
            offset = Math.PI / 2, //start sector from top
            radius,
            centerx,
            centery, 
            lastend = 0; //prev arc's end line: starting with 0

        for (var val of dataset.data) { total += val; } 

        Chart.helpers.each(meta.data.forEach( function (element, index) {
            radius = 0.9 * element._model.outerRadius - element._model.innerRadius;
            centerx = element._model.x;
            centery = element._model.y;
            var thispart = dataset.data[index],
                arcsector = Math.PI * (2 * thispart / total);
            if (element.hasValue() && dataset.data[index] > 0) {
              labelxy.push(lastend + arcsector / 2 + Math.PI + offset);
            }
            else {
              labelxy.push(-1);
            }
            lastend += arcsector;
        }), self)

        var lradius = radius * 3 / 4;
        for (var idx in labelxy) {
          if (labelxy[idx] === -1) continue;
          var langle = labelxy[idx],
              dx = centerx + lradius * Math.cos(langle),
              dy = centery + lradius * Math.sin(langle),
              val = Math.round(dataset.data[idx] / total * 100);
          ctx.fillText(val + '%', dx, dy);
        }

    }), self);
  }
},

Answer 1

ChartJs 版本 > 2.1.5 的解决方案:

Chart.pluginService.register({
  beforeRender: function (chart) {
    if (chart.config.options.showAllTooltips) {
        // create an array of tooltips
        // we can't use the chart tooltip because there is only one tooltip per chart
        chart.pluginTooltips = [];
        chart.config.data.datasets.forEach(function (dataset, i) {
            chart.getDatasetMeta(i).data.forEach(function (sector, j) {
                chart.pluginTooltips.push(new Chart.Tooltip({
                    _chart: chart.chart,
                    _chartInstance: chart,
                    _data: chart.data,
                    _options: chart.options.tooltips,
                    _active: [sector]
                }, chart));
            });
        });

        // turn off normal tooltips
        chart.options.tooltips.enabled = false;
    }
},
  afterDraw: function (chart, easing) {
    if (chart.config.options.showAllTooltips) {
        // we don't want the permanent tooltips to animate, so don't do anything till the animation runs atleast once
        if (!chart.allTooltipsOnce) {
            if (easing !== 1)
                return;
            chart.allTooltipsOnce = true;
        }

        // turn on tooltips
        chart.options.tooltips.enabled = true;
        Chart.helpers.each(chart.pluginTooltips, function (tooltip) {
            tooltip.initialize();
            tooltip.update();
            // we don't actually need this since we are not animating tooltips
            tooltip.pivot();
            tooltip.transition(easing).draw();
        });
        chart.options.tooltips.enabled = false;
    }
  }
});