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watch

订阅输入更改

</> watch: UseFormWatch

此方法将监视指定的输入并返回它们的值。它对于渲染输入值和确定按条件渲染什么很有用。

¥This method will watch specified inputs and return their values. It is useful to render input value and for determining what to render by condition.

重载

¥Overloads

此功能主要有两个用途：

¥This function mainly serves two purposes:

  • watch(name: string, defaultValue?): unknown
  • watch(names: string[], defaultValue?): {[key:string]: unknown}
  • watch(): {[key:string]: unknown}

下面是这四个重载中的每一个的解释。

¥The explanation of each of these four overloads follows below.

1-a.监视单个字段 watch(name: string, defaultValue?: unknown): unknown

¥1-a. Watching single field watch(name: string, defaultValue?: unknown): unknown

监视并订阅渲染之外使用的单个字段。

¥Watch and subscribe to a single field used outside of render.

参数

¥Params

名称类型描述
namestring字段名称
defaultValueunknown可选。字段的默认值

返回单个字段值。

¥Returns the single field value.

const name = watch("name")

1-b.监视某些字段 watch(names: string[], defaultValue?: {[key:string]: unknown}): unknown[]

¥1-b. Watching some fields watch(names: string[], defaultValue?: {[key:string]: unknown}): unknown[]

监视并订阅渲染之外使用的字段数组。

¥Watch and subscribe to an array of fields used outside of render.

参数

¥Params

名称类型描述
namesstring[]字段名称
defaultValue{[key:string]: unknown}可选。字段的默认值

返回字段值数组。

¥Returns an array of field values.

const [name, name1] = watch(["name", "name1"])

1-c.监视整个表单 watch(): {[key:string]: unknown}

¥1-c. Watching the entire form watch(): {[key:string]: unknown}

根据 onChange 监视并订阅整个表单的更新/更改，并在 useForm 上重新渲染。

¥Watch and subscribe to the entire form update/change based on onChange and re-render at the useForm.

参数无

¥Params None

返回整个表单值。

¥Returns the entire form values.

const formValues = watch()

2. Deprecated: 考虑使用或迁移到 subscribe。使用回调函数 watch(callback: (data, { name, type }) => void, defaultValues?: {[key:string]: unknown}): { unsubscribe: () => void } 进行监视

¥ Deprecated: consider use or migrate to subscribe. Watching with callback fn watch(callback: (data, { name, type }) => void, defaultValues?: {[key:string]: unknown}): { unsubscribe: () => void }

订阅字段更新/更改而不触发重新渲染。

¥Subscribe to field update/change without trigger re-render.

参数

¥Params

名称类型描述
callback(data, { name, type }) => void回调函数以订阅所有字段更改
defaultValues{[key:string]: unknown}可选。整个表单的默认值

返回具有 unsubscribe 函数的对象。

¥Returns object with unsubscribe function.

规则

¥Rules

  • 当 defaultValue 未定义时，watch 的第一次渲染将返回 undefined，因为它在 register 之前被调用。建议在 useForm 处提供 defaultValues 以避免这种行为，但你可以将内联 defaultValue 设置为第二个参数。

    ¥When defaultValue is not defined, the first render of watch will return undefined because it is called before register. It's recommended to provide defaultValues at useForm to avoid this behaviour, but you can set the inline defaultValue as the second argument.

  • 当 defaultValue 和 defaultValues 都提供时，将返回 defaultValue。

    ¥When both defaultValue and defaultValues are supplied, defaultValue will be returned.

  • 此 API 将在应用或表单的根部触发重新渲染，如果你遇到性能问题，请考虑使用回调或 useWatch api。

    ¥This API will trigger re-render at the root of your app or form, consider using a callback or the useWatch api if you are experiencing performance issues.

  • watch 结果针对渲染阶段而不是 useEffect 的 deps 进行了优化，为了检测值更新，你可能需要使用外部自定义钩子进行值比较。

    ¥watch result is optimised for render phase instead of useEffect's deps, to detect value update you may want to use an external custom hook for value comparison.

示例：

¥Examples:

在表单中监视

¥Watch in a Form

CodeSandbox TS
import { useForm } from "react-hook-form"


interface IFormInputs {
  name: string
  showAge: boolean
  age: number
}


function App() {
  const {
    register,
    watch,
    formState: { errors },
    handleSubmit,
  } = useForm<IFormInputs>()
  const watchShowAge = watch("showAge", false) // you can supply default value as second argument
  const watchAllFields = watch() // when pass nothing as argument, you are watching everything
  const watchFields = watch(["showAge", "age"]) // you can also target specific fields by their names


  const onSubmit = (data: IFormInputs) => console.log(data)


  return (
    <>
      <form onSubmit={handleSubmit(onSubmit)}>
        <input {...register("name", { required: true, maxLength: 50 })} />
        <input type="checkbox" {...register("showAge")} />
        {/* based on yes selection to display Age Input*/}
        {watchShowAge && (
          <input type="number" {...register("age", { min: 50 })} />
        )}
        <input type="submit" />
      </form>
    </>
  )
}
CodeSandbox JS
import { useForm } from "react-hook-form"


function App() {
  const {
    register,
    watch,
    formState: { errors },
    handleSubmit,
  } = useForm()
  const watchShowAge = watch("showAge", false) // you can supply default value as second argument
  const watchAllFields = watch() // when pass nothing as argument, you are watching everything
  const watchFields = watch(["showAge", "number"]) // you can also target specific fields by their names


  const onSubmit = (data) => console.log(data)


  return (
    <>
      <form onSubmit={handleSubmit(onSubmit)}>
        <input type="checkbox" {...register("showAge")} />


        {/* based on yes selection to display Age Input*/}
        {watchShowAge && (
          <input type="number" {...register("age", { min: 50 })} />
        )}


        <input type="submit" />
      </form>
    </>
  )
}

在字段数组中监视

¥Watch in Field Array

CodeSandbox TS
import * as React from "react"
import { useForm, useFieldArray } from "react-hook-form"


type FormValues = {
  test: {
    firstName: string
    lastName: string
  }[]
}


function App() {
  const { register, control, handleSubmit, watch } = useForm<FormValues>()
  const { fields, remove, append } = useFieldArray({
    name: "test",
    control,
  })
  const onSubmit = (data: FormValues) => console.log(data)


  console.log(watch("test"))


  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      {fields.map((field, index) => {
        return (
          <div key={field.id}>
            <input
              defaultValue={field.firstName}
              {...register(`test.${index}.firstName`)}
            />
            <input
              defaultValue={field.lastName}
              {...register(`test.${index}.lastName`)}
            />
            <button type="button" onClick={() => remove(index)}>
              Remove
            </button>
          </div>
        )
      })}
      <button
        type="button"
        onClick={() =>
          append({
            firstName: "bill" + renderCount,
            lastName: "luo" + renderCount,
          })
        }
      >
        Append
      </button>
    </form>
  )
}
CodeSandbox JS
import * as React from "react"
import { useForm, useFieldArray } from "react-hook-form"


function App() {
  const { register, control, handleSubmit, watch } = useForm()
  const { fields, remove, append } = useFieldArray({
    name: "test",
    control,
  })
  const onSubmit = (data) => console.log(data)


  console.log(watch("test"))


  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      {fields.map((field, index) => {
        return (
          <div key={field.id}>
            <input
              defaultValue={field.firstName}
              {...register(`test.${index}.firstName`)}
            />
            <input
              defaultValue={field.lastName}
              {...register(`test.${index}.lastName`)}
            />
            <button type="button" onClick={() => remove(index)}>
              Remove
            </button>
          </div>
        )
      })}
      <button
        type="button"
        onClick={() =>
          append({
            firstName: "bill" + renderCount,
            lastName: "luo" + renderCount,
          })
        }
      >
        Append
      </button>
    </form>
  )
}

视频

¥Video