[英]Am trying out react with a simple counter. Within the console.log it works perfectly but within the user interface it doesn't update the counter
[英]Simple React counter not working, also can't console.log useState variables?
我對React還是比較陌生(一個月前才開始學習),並且試圖在頁面上顯示一個簡單的計數器,但它只會更新一次。 另外,每當我console.log()
狀態變量時,它們始終為空,但是由於我將它們添加到頁面上的輸出中,因此我可以看到它們正在更新,但是仍然無法console.log這些值? 是什么賦予了? 我一定做錯了,但看不出原因。
這是codesandbox中的“問題”的演示 。
這是代碼:
import React, { useState } from "react";
import "jqwidgets-scripts/jqwidgets/styles/jqx.base.css";
import JqxInput from "jqwidgets-scripts/jqwidgets-react-tsx/jqxinput";
const MyForm2: React.FC = () => {
const [count, setCount] = useState(0);
const [email, setEmail] = useState("");
const [name, setName] = useState("");
const onEmailChange = (e?: any) => {
setCount(count + 1);
setEmail(e.args.value);
console.log('You typed: ' + e.args.value);
console.log("name: " + name + ", email: " + email);
};
const onNameChange = (e?: any) => {
setCount(count + 1);
setName(e.args.value);
};
return (
<div>
Name:{" "}
<JqxInput value={name} onChange={(e: any) => setName(e.args.value)} />
Email: <JqxInput value={email} onChange={onEmailChange} />
<p>Count: {count}</p>
<p>email: {email}</p>
<p>name: {name}</p>
</div>
);
};
export default MyForm2;
謝謝。 我期待發現我的壯觀錯誤:-)
當下一個狀態取決於上一個狀態時,您應該將函數更新程序作為參數傳遞給setState
。 因此更改為:
setCount((count) => count + 1)
onNameChange
關閉Java語言 , onNameChange
范圍根據count
變量關閉:
const MyForm2: React.FC = () => {
const [count, setCount] = useState(0);
const [email, setEmail] = useState('');
const [name, setName] = useState('');
const onEmailChange = (e?: any) => {
setCount(prev => prev + 1); // <-- no closure, use previous state
// Render as expected.
setEmail(e.args.value);
};
const onNameChange = (e?: any) => {
setCount(count + 1); // <-- `count` always 0;
// Will always redner the value '1'.
setName(e.args.value);
};
return (
<div>
Name: <JqxInput value={name} onChange={onNameChange} />
Email: <JqxInput value={email} onChange={onEmailChange} />
<p>Count: {count}</p>
</div>
);
};
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