setState（）：不要直接改变状态。使用setState（）

Question

运行代码时出现以下警告：

第48行：不要直接改变状态。使用setState（）react / no-direct-mutation-state

此警告涉及以下代码行：

updateDelay(prediction_arr,prediction_dep) {
  this.state.chartDataWake = [...this.state.chartDataWake, {wake: this.state.wake===84.73 ? "H" : (this.state.wake===14.78 ? "M" : "L"), delay: prediction_arr}];
  this.state.chartDataTurnaround = [...this.state.chartDataTurnaround, {turnaround: this.state.schedTurnd, delay: prediction_arr}];

  this.setState({
    prediction_arr: prediction_arr,
    prediction_dep: prediction_dep,
    delay_arr_cat: prediction_arr===0 ? "<15" : (prediction_arr===1 ? "[15; 45]" : ">45")
  });
};

我明白我应该把所有声明都放在this.setState({里面。然而，我不清楚我应该如何改变

this.state.chartDataTurnaround = [...this.state.chartDataTurnaround, {turnaround: this.state.schedTurnd, delay: prediction_arr}];

为了能够编译代码。

Answer 1

1-不要直接改变状态使用setState，所以删除前两行。

2-因为setState is async和你正在根据以前的值更新状态，所以使用updater function，意味着在setState中传递一个函数并在该函数中使用prevState值。

像这样：

updateDelay(prediction_arr,prediction_dep) {
  this.setState(prevState => ({
    prediction_arr: prediction_arr,
    prediction_dep: prediction_dep,
    delay_arr_cat: prediction_arr===0 ? "<15" : (prediction_arr===1 ? "[15; 45]" : ">45"),

    chartDataWake: [
      ...prevState.chartDataWake,
      {wake: prevState.wake===84.73 ? "H" : (prevState.wake===14.78 ? "M" : "L"), delay: prediction_arr}
    ],

    chartDataTurnaround: [
      ...prevState.chartDataTurnaround,
      {turnaround: prevState.schedTurnd, delay: prediction_arr}
    ]
  }));
};

Answer 2

切勿使用this.state.YOUR_VARIABLE = something修改状态

如果你想要，并从你所做的片段中看到，将prevState复制到你的新状态并能够向它添加新元素，你应该使用对象克隆来首先复制先前的状态，然后添加更多你想要这个副本的元素。

updateDelay(prediction_arr, prediction_dep) {
 const newChartDataWake = [...this.state.chartDataWake, {
  wake: this.state.wake === 84.73 ? "H" : (this.state.wake === 14.78 ? "M" : "L"),
  delay: prediction_arr
 }];

 const newChartDataTurnaround = [...prevState.chartDataTurnaround, {
  turnaround: prevState.schedTurnd,
  delay: prediction_arr
 }]



 this.setState(prevState => {
  return {
   chartDataWake: newChartDataWake
   chartDataTurnaround: newChartDataTurnaround
   prediction_arr: prediction_arr,
   prediction_dep: prediction_dep,
   delay_arr_cat: prediction_arr === 0 ? "<15" : (prediction_arr === 1 ? "[15; 45]" : ">45")
  }
 });
};

Answer 3

您应该使用setState的回调，它将以前的State作为参数。

this.setState((prevState,props) => 
({
   chartDataWake:[...prevState.chartDataWake, {wake: prevState.wake===84.73 
       ? "H" : (prevState.wake===14.78 ? "M" : "L"), delay: prediction_arr}],
   chartDataTurnaround = [...prevState.chartDataTurnaround, {turnaround: 
      prevState.schedTurnd, delay: prediction_arr}],
   prediction_arr: prediction_arr,
   prediction_dep: prediction_dep,
   delay_arr_cat: prediction_arr===0 ? "<15" : (prediction_arr===1 ? "[15; 
      45]" : ">45")
})