(Vue, ChartJS) 从子组件画布上下文为图表创建渐变背景

问题描述

我想给我的图表一个渐变背景颜色，但我无法访问画布上下文，因为我的图表在我编写的包装器组件中呈现.

I want to give my chart a gradient background color, but I can't access the canvas context as my chart gets rendered in a wrapper component I wrote.

我想要实现的目标:

我的实际包装器看起来像这样:

My actual wrapper rather looks like this:

<script>
import { Line, mixins } from "vue-chartjs";
const { reactiveProp } = mixins;

export default {
  extends: Line,
  mixins: [reactiveProp],
  props: ["options"],
  components: {},
  mounted() {
    // this.chartData is created in the mixin
    this.renderChart(this.chartData, this.options);
  }
};
</script>

我将包装器用于不同的折线图，并让它的父级传递相关数据 - 有时每页多次使用包装器组件.

I'm using my wrapper for different line charts and let it's parent pass down the relevant data - sometimes using the wrapper component several times per page.

所有配置(选项、标签等)都在使用包装器的父组件中完成.

All configuration (options, labels, etc.) gets done in the parent component, which uses the wrapper.

有没有办法将画布上下文从包装器获取到使用包装器的父组件?

Is there a way to get the canvas context from the wrapper to the parent component, which uses the wrapper?

要创建渐变，你需要这样的东西:

To create the gradient, you need something like this:

this.gradient = this.$refs.canvas
  .getContext("2d")
  .createLinearGradient(0, 0, 0, 450);

this.gradient.addColorStop(0, "rgba(255, 0,0, 0.5)");
this.gradient.addColorStop(0.5, "rgba(255, 0, 0, 0.25)");
this.gradient.addColorStop(1, "rgba(255, 0, 0, 0)");

..but this.$refs.canvas 在父组件中未定义，这使我无法获取上下文，因此无法创建渐变.

..but this.$refs.canvas is undefined in the parent component, which prevents me from getting the context, so I can't create a gradient.

推荐答案

您可以在图表组件中访问 this.$refs.canvas.如果你想从你的父组件访问它，有几种方法.

You can access this.$refs.canvas in your chart component.If you want to access it from your parent component there are several ways.

快速不干净的方法就结束了.$childrenhttps://vuejs.org/v2/api/#vm-children

The fast unclean way is over this.$childrenhttps://vuejs.org/v2/api/#vm-children

更好的方法是将渐变内容设置为自己的方法，并将所有数据作为道具传递给图表组件.

A better way would be to setup the gradient stuff into a own method and pass in all data as props to your chart component.

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