Question

我正在创建一个反应向导组件，并希望使用上下文在“父子之间传递数据”

所以我创建了一个向导，上下文，提供程序和自定义钩子，但是问题是，如果我尝试在向导组件上使用上下文，它将无法显示正确的信息

（请参阅https://codesandbox.io/embed/wizardwitcontext-rfpui）

如何做到这一点，以便我可以依靠向导本身上下文中的数据，以便将登录名转移到自定义钩子？

useWizard.js：

import React, { useContext, useEffect } from "react";
import { WizardContext } from "./WizardContext";

const useWizard = () => {
  const [state, setState] = useContext(WizardContext);

  function setMaxSteps(maxSteps) {
    setState(state => ({ ...state, maxSteps }));
  }
  function moveToStep(index) {
    if (state.maxSteps && state.maxSteps > index) {
      setState({ ...state, currentStep: index });
      return index;
    }
    return state.currentStep;
  }

  function back() {
    if (state.maxSteps) {
      if (state.currentStep > 0) {
        setState({ ...state, currentStep: state.currentStep - 1 });
        window.scrollTo(0, 0);
      }
    }
  }

  //move back a step
  function next() {
    if (state.currentStep < state.maxSteps) {
      setState({ ...state, currentStep: state.currentStep + 1 });
      window.scrollTo(0, 0);
    }
  }

  return {
    setMaxSteps,
    moveToStep,
    back,
    next,
    maxSteps: state.maxSteps,
    currentStep: state.currentStep,
    state
  };
};

export default useWizard;

Wizard.jsx：

const { state, currentStep, back, next, maxSteps, setMaxSteps } = useWizard();

return (
    <div className="wizard">
      <WizardProvider
        maxSteps={React.Children.count(props.children)}
        currentStep={0}
      >
        {/* <div className="wizard__upper">
          <ProgressIndicator currentIndex={selected} onChange={onClick}>
            {steps}
          </ProgressIndicator>

          <Button id="wizardCloseBtn" kind="ghost" onClick={onClose}>
            <Icon icon={iconHeaderClose} />
          </Button>
        </div> */}
        <div className="wizard__separator" />
        <div className="wizard__content">
          {`in wizard: cur=${currentStep}, max=${maxSteps}`}
          {/* {getContentAt(0)} */}
          {stepContentWithProps}
        </div>

        {/* <div className="wizard__buttons">
          {showBack && (
            <Link id="back" onClick={back}>
              back
            </Link>
          )}
          {showNext && (
            <button id="next" onClick={next} kind="secondary">
              Next Step
            </button>
          )}
        </div> */}
      </WizardProvider>
    </div>
  );

第二步：

import React, { useState, useContext, useEffect } from "react";
import useWizard from "./useWizard";

function Step2(props) {
  const {
    currentStep,
    moveToStep,
    maxSteps,
    setMaxSteps,
    next,
    prev
  } = useWizard();

  return (
    <div>
      <p>Step 2</p>
      {`in step2 (inner child of wizard): cur=${currentStep} see that cur !== cur from wizard above`}
      <br />
      <button onClick={() => moveToStep(1)}>
        Click me to change current step
      </button>
    </div>
  );
}

export default Step2;

最终结果是：

in wizard: cur=undefined, max=undefined
p1

in index.js: cur=undefined
Step 2

in step2 (inner child of wizard): cur=0 see that cur !== cur from wizard above

Answer 1

上下文是从组件树上方最近的提供程序派生的。来自react docs。

const value = useContext（MyContext）;

接受一个上下文对象（从React.createContext返回的值）并返回该上下文的当前上下文值。当前上下文值由树中调用组件上方最近的值prop决定。

在这种情况下，您有2个选项。

1。您需要在提供程序中包装App（index.js）组件。

或

2。让向导组件成为提供者，并尝试在子组件中使用useContext挂钩。

演示：https://stackblitz.com/edit/react-msac8q

希望这会有所帮助

Answer 2

您以与useContext相同的级别呼叫Context.Provider：

function Wizard(props) {
  // useWizard calls useContext
  const { state, currentStep, back, next, maxSteps, setMaxSteps } = useWizard();

  return (
    <div className="wizard">
      <WizardProvider
        maxSteps={React.Children.count(props.children)}
        currentStep={0}
      >
        <div className="wizard__content">
          {`in wizard: cur=${currentStep}, max=${maxSteps}`}
        </div>
      </WizardProvider>
    </div>
  );
}

您需要更改自己的结构，并在useContext个孩子中致电Provider。

function Wizard(props) {
  // useWizard calls useContext
  const { state, currentStep, back, next, maxSteps, setMaxSteps } = useWizard();

  return (
//      v You trying to get Provider's value here
    <div className="wizard">
      <WizardProvider
        maxSteps={React.Children.count(props.children)}
        currentStep={0}
      >
//      v useContext available within the children
        <ComponentA />
        <ComponentB />
      </WizardProvider>
    </div>
  );
}

请参阅Context API，useContext。

Answer 3

由于这篇文章，我找到了解决方案：https://dev.to/email2vimalraj/react-hooks-lift-up--pass-down-state-using-usecontext-and-usereducer-5ai0 所描述的解决方案是在向导文件上创建一个化简器，以便向导可以访问其数据以及子进程：

Wizard.jsx

import React, {
  useState,
  useEffect,
  useLayoutEffect,
  useContext,
  useReducer
} from "react";
import PropTypes from "prop-types";
import "./wizard.scss";

import {
  WizardContext,
  wizardReducer,
  SET_CURRENT_STEP,
  SET_MAX_STEPS,
  BACK,
  NEXT
} from "./WizardContext";

function StepContent(props) {
  const { selected, children, ...other } = props;

  return (
    <li {...other} selected={selected}>
      {children}
    </li>
  );
}

function Wizard(props) {
  const { onClose, onChange, pageContentClassName } = props;

  function onClick(index) {
    dispatch({ type: SET_CURRENT_STEP, currentStep: index });
    // setSelected(index);
  }

  //get the progressBar steps
  const steps = React.Children.map(props.children, page => {
    const { id, label, description } = page.props;
    return <div id={id} label={label} description={description} />;
  });

  function getContentAt(index) {
    return stepContentWithProps[index];
  }

  const stepsWithProps = React.Children.map(props.children, (step, index) => {
    const newStep = React.cloneElement(step, {});
    return newStep;
  });

  const stepContentWithProps = stepsWithProps.map((step, index) => {
    const { children } = step.props;

    return (
      <StepContent key={index} className={pageContentClassName}>
        {children}
      </StepContent>
    );
  });

  const initialState = {
    maxSteps: React.Children.count(props.children),
    currentStep: 0
  };
  const [wizardData, dispatch] = useReducer(wizardReducer, initialState);

  return (
    <div className="wizard">
      <p>This text is in wizard: currentStep={wizardData.currentStep}</p>
      <WizardContext.Provider value={{ wizardData, dispatch }}>
        <div className="wizard__upper">
          <ul currentIndex={wizardData.currentStep} onChange={onClick}>
            {steps}
          </ul>
        </div>
        <div className="wizard__separator" />
        <div className="wizard__content">{stepsWithProps}</div>
        <div>
          <button onClick={() => dispatch({ type: BACK })}>Back</button>
          <button onClick={() => dispatch({ type: NEXT })}>Next</button>
        </div>
      </WizardContext.Provider>
    </div>
  );
}

Wizard.propTypes = {
  /**
   * Specify the text to be read by screen-readers when visiting the <Tabs>
   * component
   */
  ariaLabel: PropTypes.string,

  /**
   * Pass in a collection of <Tab> children to be rendered depending on the
   * currently selected tab
   */
  children: PropTypes.node,

  /**
   * Provide a className that is applied to the <PageContent> components
   */
  pageContentClassName: PropTypes.string
};

export default Wizard;

WizardContext.jsx

import React, { createContext } from "react";

export const WizardContext = React.createContext(null);

export const SET_MAX_STEPS = "SET_MAX_STEPS";
export const SET_CURRENT_STEP = "SET_CURRENT_STEP";
export const BACK = "BACK";
export const NEXT = "NEXT";
export const SHOW_BACK = "SHOW_BACK";
export const SHOW_NEXT = "SHOW_NEXT";

export function wizardReducer(state, action) {
  switch (action.type) {
    case SET_MAX_STEPS:
      return {
        ...state,
        maxSteps: action.maxSteps
      };
    case SET_CURRENT_STEP:
      if (action.currentStep >= state.maxSteps) return state;

      return {
        ...state,
        currentStep: action.currentStep
      };
    case BACK:
      if (state.currentStep === 0) return state;

      return {
        ...state,
        currentStep: state.currentStep - 1
      };
    case NEXT:
      if (state.currentStep >= state.maxSteps - 1) return state;

      return {
        ...state,
        currentStep: state.currentStep + 1
      };
    default:
      return state;
  }
}

Index.js

import React, { useState } from "react";
import ReactDOM from "react-dom";

import "./styles.css";
import Wizard from "./Wizard";
import Cmp2 from "./Cmp2";

function App() {
  const [wizardVisible, setWizardVisible] = useState(false);
  return (
    <div className="App">
      <h1>
        Wizard: why cant I see currentStep in wizard
        <br />
        (WORKING NOW!!!)
      </h1>
      <Wizard>
        <div label="ddd">This is step1</div>
        <Cmp2 />
        <div label="ddd">This is step3</div>
      </Wizard>
    </div>
  );
}

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

Cmp2.jsx

import React, { useState, useContext, useEffect } from "react";
import { WizardContext, SET_CURRENT_STEP } from "./WizardContext";

function Cmp2(props) {
  const { wizardData, dispatch } = useContext(WizardContext);

  return (
    <div>
      <br />
      <p>This is Step 2</p>
      {`in step2 (inner child of wizard): cur=${wizardData.currentStep}`}
      <br />
      <button
        onClick={() => dispatch({ type: SET_CURRENT_STEP, currentStep: 1 })}
      >
        Click me to change current step
      </button>
      <br />
      <br />
    </div>
  );
}

export default Cmp2;

现在，我需要找到使它可访问的方法，它的工作原理很好，但是当我尝试创建一个自定义钩子（导入上下文）时，当尝试使用自定义钩子时，上下文为null（这是可以理解的，因为它是在提供程序之前在向导中调用的），如何在此处添加更好的功能？

这是一个可行的解决方案（不带钩）：

https://codesandbox.io/embed/wizardwitcontext-working-3lxhd

Answer 4

我认为由于我们不能在与 Provider 相同的组件中使用 useContext()，我认为我们可以做一些解决方法，我认为这将有助于在页面/屏幕等主要组件中使用

 // This will be your child component  
 function Wizard(props) {
  // useWizard calls useContext
  const { state, currentStep, back, next, maxSteps, setMaxSteps } = useWizard();

  return (
    <div className="wizard">
        <div className="wizard__content">
          {`in wizard: cur=${currentStep}, max=${maxSteps}`}
        </div>
    </div>
  );
}

// This is your main Page
export default function WizardPage(){
  return <WizardProvider 
          maxSteps={React.Children.count(props.children)}
          currentStep={0}>
            <Wizard /> 
   </WizardProvider>
}

如何在同一个组件中使用react useContext来显示上下文中的数据

4 个答案: