我的组件有表单输入字段。这些使用了一个 useState Hook ,每个输入字段都有它们的值和 setValue。我想优化我的组件,以便输入字段使用我称为 useFormInput 的相同自定义 Hook
灵感来自 Dan Abramov https://youtu.be/dpw9EHDh2bM见 49:42
这非常有效。但是现在我想在创建新练习后更新用户名。这是在 onSubmit 方法中。但我不确定该怎么做。在重构之前,我可以使用 setUserName(),但现在用户名由通用自定义 Hook 函数 useFormInput 设置
用户名有一个 onChange 方法,所以我想我也许可以使用它。但是,这使用了 e.target.value,因为它用于输入字段。
组件: 我把setUserName('')注释掉了,这里我要更新用户名
const CreateExercise = () => {
const inputEl = useRef(null)
const username = useFormInput('')
const description = useFormInput('')
const duration = useFormInput(0)
const date = useFormInput(new Date())
const [users, setUsers] = useState([])
useEffect(() => {
axios
.get('http://localhost:5000/users/')
.then(res => {
if (res.data.length > 0) {
setUsers(res.data.map(user => user.username))
}
})
.catch(err => console.log(err))
}, [])
const onSubmit = e => {
e.preventDefault()
const exercise = {
username: username.value,
description: description.value,
duration: duration.value,
date: date.value
}
axios
.post('http://localhost:5000/exercises/add', exercise)
.then(res => console.log(res.data))
debugger
// setUsername('')
window.location = '/'
}
自定义 Hook useFormInput:
const useFormInput = initialValue => {
const [value, setValue] = useState(initialValue)
const handleChange = e => {
const newValue = e.target ? e.target.value : e
setValue(newValue)
}
return {
value,
onChange: handleChange
}
}
我希望用户名状态中的值更新为空字符串''
最佳答案
我建议将所有状态组合到一个对象中,而不是尝试维护超过 1 个状态。然后您可以将所有内容移动到您的自定义 Hook 中。此外,始终确保您处理任何错误并将其传达给用户。
工作示例:
作为对象的状态
hooks/useFormHandler(下面定义的 API
是一个具有模拟 API 调用功能的对象——您将用真正的 API 调用替换它。此外,如果您想要使此 Hook 可重用于其他 form
组件,则需要从自定义 Hook 和放置中删除 useEffect
和 handleSubmit
函数它们在指定的功能组件中)
import { useCallback, useEffect, useState } from "react";
import API from "../../API";
// create a custom useFormHandler hook that returns initial values,
// a handleChange function to update the field values and a handleSubmit
// function to handle form submissions.
const useFormHandler = initialState => {
const [values, setValues] = useState(initialState);
// on initial load this will attempt to fetch users and set them to state
// otherwise, if it fails, it'll set an error to state.
useEffect(() => {
API.get("http://localhost:5000/users/")
.then(res => {
if (res.data.length > 0) {
setValues(prevState => ({
...prevState,
users: res.data.map(({ username }) => username)
}));
} else {
setValues(prevState => ({
...prevState,
error: "Unable to locate users."
}));
}
})
.catch(err =>
setValues(prevState => ({ ...prevState, error: err.toString() }))
);
}, []);
// the handleChange function will first deconstruct e.target.name and
// e.target.value, then in the setValues callback function, it'll
// spread out any previous state before updating the changed field via
// [name] (e.target.name) and updating it with "value" (e.target.value)
const handleChange = useCallback(
({ target: { name, value } }) =>
setValues(prevState => ({ ...prevState, error: "", [name]: value })),
[]
);
// the handleSubmit function will send a request to the API, if it
// succeeds, it'll print a message and reset the form values, otherwise,
// if it fails, it'll set an error to state.
const handleSubmit = useCallback(
e => {
e.preventDefault();
const exercise = {
username: values.username,
description: values.description,
duration: values.duration,
date: values.date
};
// if any fields are empty, display an error
const emptyFields = Object.keys(exercise).some(field => !values[field]);
if (emptyFields) {
setValues(prevState => ({
...prevState,
error: "Please fill out all fields!"
}));
return;
}
API.post("http://localhost:5000/exercises/add", exercise)
.then(res => {
alert(JSON.stringify(res.message, null, 4));
setValues(prevState => ({ ...prevState, ...initialState }));
})
.catch(err =>
setValues(prevState => ({ ...prevState, error: err.toString() }))
);
},
[initialState, setValues, values]
);
return {
handleChange,
handleSubmit,
values
};
};
export default useFormHandler;
组件/CreateExerciseForm
import isEmpty from "lodash/isEmpty";
import React, { Fragment } from "react";
import { FaCalendarPlus } from "react-icons/fa";
import Spinner from "react-spinkit";
import Button from "../Button";
import Input from "../Input";
import Select from "../Select";
import useFormHandler from "../../hooks/useFormHandler";
const fields = [
{ type: "text", name: "description", placeholder: "Exercise Description" },
{ type: "number", name: "duration", placeholder: "Duration (in minutes)" },
{
type: "date",
name: "date",
placeholder: "Date"
}
];
// utilize the custom useFormHandler hook within a functional component and
// pass it an object with some initial state.
const CreateExerciseForm = () => {
const { values, handleChange, handleSubmit } = useFormHandler({
username: "",
description: "",
duration: "",
date: "",
error: ""
});
// the below will show a spinner if "values.users" hasn't been fulfilled yet
// else, it'll show the form fields. in addition, if there's ever a
// "values.error", it'll be displayed to the user.
return (
<form
style={{ width: 500, margin: "0 auto", textAlign: "center" }}
onSubmit={handleSubmit}
>
{isEmpty(values.users) ? (
<Spinner name="line-scale" />
) : (
<Fragment>
<Select
name="username"
placeholder="Select a user..."
handleChange={handleChange}
value={values.username}
selectOptions={values.users}
style={{ width: "100%" }}
/>
{fields.map(({ name, type, placeholder }) => (
<Input
key={name}
type={type}
name={name}
placeholder={placeholder}
onChange={handleChange}
value={values[name]}
/>
))}
<Button type="submit">
<FaCalendarPlus style={{ position: "relative", top: 2 }} />
Create Exercise
</Button>
</Fragment>
)}
{values.error && <p>{values.error}</p>}
</form>
);
};
export default CreateExerciseForm;
状态为独立的数据类型
或者,如果您坚持使用分离状态,则在 useFormInput
Hook 中创建一个 resetValue
函数:
const useFormInput = initialValue => {
// initialize state from "initialValue"
const [value, setValue] = useState(initialValue)
// handle changes to the "value" state via updating it
// with e.target.value
const handleChange = useCallback(({ target: { value } => {
setValue(value)
}, []);
// reset the value back to initialValue
const resetValue = useCallback(() => {
setValue(initialValue);
}, []);
return {
value,
handleChange,
resetValue
}
}
然后,解构用户名的属性(以及其他状态,如果需要的话):
const CreateExercise = () => {
// use ES6 destructure and aliasing to extract and rename the
// "value" (as username), "handleChange" function (as
// handleUsernameChange) and "resetValue" function (as resetUsername)
const {
value: username,
handleChange: handleUsernameChange,
resetValue: resetUsername
} = useFormInput('')
...other form state
...useEffect(() => {}, [])
const handleSubmit = useCallback(e => {
e.preventDefault();
const exercise = {
username: username,
description: description,
duration: duration,
date: date
};
axios
.post('http://localhost:5000/exercises/add', exercise)
.then(res => {
console.log(res.data)
// only reset the username if the exercise was successfully
// created
resetUsername();
})
.catch(err => console.log(err.toString());
}, [date, description, duration, resetUsername, username]);
return ( ...form )
}
关于javascript - 如何更新使用自定义 Hook 的变量的状态值,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/56413550/