處理 promise 以進行反應渲染

Question

我有以下代碼：

async function determineCounters() { 
 #do something
}



determineCounters()
.then(response => {
  let var2 = response[0];
  let var3 = response[1];
});

const [activityCounter, setActivityCounter] = React.useState(var2);
const [awardCounter, setAwardCounter] = React.useState(var3);

return(
   #uses activityCounter and awardCounter
)

當我運行此代碼時，activityCounter 和 AwardCounter 沒有填充正確的 var2 和 var3 值，這會破壞返回中顯示的內容。 如何延遲計數器和返回以等待 var2 和 var3 完成？

Answer 1

您需要在組件頂部聲明 state 變量，並將它們設置為：

determineCounters()
.then(response => {
  setActivityCounter(response[0])
  setAwardCounter(response[1])
});

當你聲明它們時，你會給它們一個初始的 state：

const [activityCounter, setActivityCounter] = React.useState(null); // or whatever you need as initial state

Answer 2

將then包裹在useEffect

const [activityCounter, setActivityCounter] = React.useState(null);
const [awardCounter, setAwardCounter] = React.useState(null);

React.useEffect(() => {
  determineCounters().then((response) => {
    let var2 = response[0];
    let var3 = response[1];
    setActivityCounter(var2);
    setAwardCounter(var3);
  });
}, []);