[英]How to write if else statement in reactJS when using useEffect?
以下是我用来返回 Plotly 图形的代码,我需要在这里做的是当图形数据为空或图形上没有任何内容时,我需要返回一条消息或不同的布局。 如果图表没有数据,则使用默认内容,例如没有可用数据。 我怎么做?
import React, { useEffect } from "react"; import Plot from "react-plotly.js"; import PropTypes from "prop-types"; let dataArray; let index; let obj; function PlotlyStackedChart({ labels, data, xTitle, yTitle, mainTitle, preHeading }) { useEffect(() => { dataArray = []; for (index = 0; index < data.length; index += 1) { obj = { x: labels, y: data[index].data, type: "bar", name: data[index].name, }; dataArray.push(obj); } }, [data]); return ( <> <Plot data={dataArray} layout={{ barmode: "stack", autosize: true, title: { text: preHeading + mainTitle, y: 0.9, }, margin: { t: 225, }, xaxis: { // all "layout.xaxis" attributes: #layout-xaxis title: { text: xTitle, font: { family: "Arial Black", }, }, // more about "layout.xaxis.title": #layout-xaxis-title // dtick: 1, }, yaxis: { // all "layout.yaxis" attributes: #layout-yaxis title: { text: yTitle, font: { family: "Arial Black", }, }, // more about "layout.yaxis.title": #layout-yaxis-title }, font: { // family: "Courier New, monospace", size: 12, color: "#7f7f7f", }, legend: { bgcolor: "transparent", x: 0, y: 1.4, xanchor: "auto", traceorder: "normal", orientation: "h", }, marker: { size: 40 }, }} useResizeHandler style={{ width: "100%", height: 600 }} /> </> ); } export default PlotlyStackedChart; PlotlyStackedChart.defaultProps = { xTitle: "", yTitle: "", mainTitle: "", preHeading: "", }; // Typechecking props for the MDDatePicker PlotlyStackedChart.propTypes = { labels: PropTypes.oneOfType([PropTypes.string, PropTypes.array]).isRequired, xTitle: PropTypes.string, yTitle: PropTypes.string, mainTitle: PropTypes.string, preHeading: PropTypes.string, data: PropTypes.oneOfType([PropTypes.string, PropTypes.array, PropTypes.object]).isRequired, };
进一步解释,如果图中没有 plot 的数据,我想返回以下代码,否则返回当前检索数据的代码和图中的 plot。
return { "layout": { "xaxis": { "visible": false }, "yaxis": { "visible": false }, "annotations": [ { "text": "No matching data found", "xref": "paper", "yref": "paper", "showarrow": false, "font": { "size": 28 } } ] } }
如果没有内容,您可以尝试返回空的内容模板。
import React, { useEffect } from "react";
import Plot from "react-plotly.js";
import PropTypes from "prop-types";
let dataArray;
let index;
let obj;
function PlotlyStackedChart({ labels, data, xTitle, yTitle, mainTitle, preHeading }) {
useEffect(() => {
if(data?.length){ // <--- place condition here
dataArray = [];
for (index = 0; index < data.length; index += 1) {
obj = {
x: labels,
y: data[index].data,
type: "bar",
name: data[index].name,
};
dataArray.push(obj);
}
}
}, [data]);
// Place this conditional return
if(!data?.length) {
return <>No data found</>
}
return (
<>
<Plot
data={dataArray}
layout={{
barmode: "stack",
autosize: true,
title: {
text: preHeading + mainTitle,
y: 0.9,
},
margin: {
t: 225,
},
xaxis: {
// all "layout.xaxis" attributes: #layout-xaxis
title: {
text: xTitle,
font: {
family: "Arial Black",
},
}, // more about "layout.xaxis.title": #layout-xaxis-title
// dtick: 1,
},
yaxis: {
// all "layout.yaxis" attributes: #layout-yaxis
title: {
text: yTitle,
font: {
family: "Arial Black",
},
}, // more about "layout.yaxis.title": #layout-yaxis-title
},
font: {
// family: "Courier New, monospace",
size: 12,
color: "#7f7f7f",
},
legend: {
bgcolor: "transparent",
x: 0,
y: 1.4,
xanchor: "auto",
traceorder: "normal",
orientation: "h",
},
marker: { size: 40 },
}}
useResizeHandler
style={{ width: "100%", height: 600 }}
/>
</>
);
}
export default PlotlyStackedChart;
useEffect
与您描述的问题完全无关。
如果您想在数组为空时呈现不同的内容,请在呈现逻辑中执行,而不是作为效果。
if (data.length === 0) {
return <Loading />
} else {
return <Plot .../>
}
也就是说,你的效果逻辑被打破了。 你不能只是将一个新数组分配给一个变量并让 React 渲染它。 你没有告诉 React 它需要重新渲染。 使data
成为 state 变量(使用useState
)。
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