反应：无法读取未定义的属性“读取上下文”答案

【问题标题】：React: Cannot ready property 'readContext' of undefined反应：无法读取未定义的属性“读取上下文”
【发布时间】：2019-06-12 18:35:25
【问题描述】：

react-cache 不适用于 Suspense。

我的代码

  import React, { Suspense } from "react";
  import ReactDOM from "react-dom";
  import { unstable_createResource as createResource } from "react-cache";

    const MarkdownCache = createResource(input => {
       return new Promise(resolve => resolve(input));
    });

    const App = () => {
        return (
           <Suspense fallback={<div>Loading...</div>}>
               <Test />
           </Suspense>
        );
    }

    const Test = () => {
           const input = MarkdownCache.read("Test react cache");
           return input;
     }

const rootElement = document.getElementById("root"); ReactDOM.render(, rootElement);

我正在使用的版本：

  react: 16.8.0-alpha.0
  react-dom: 16.8.0-alpha.0
  react-cache: 2.0.0-alpha.1

【问题讨论】：

标签： reactjs react-native react-cache

【解决方案1】：

修改/替换'react-cache/cjs/react-cache.development.js'中的代码

旧 -:

var currentOwner = React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED.ReactCurrentOwner;

function readContext(Context, observedBits) {
  var dispatcher = currentOwner.currentDispatcher;
  if (dispatcher === null) {
    throw new Error('react-cache: read and preload may only be called from within a ' + "component's render. They are not supported in event handlers or " + 'lifecycle methods.');
  }
  return dispatcher.readContext(Context, observedBits);
}

新 -:

const ReactCurrentDispatcher =
  React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED
    .ReactCurrentDispatcher;

function readContext(Context, observedBits) {
  const dispatcher = ReactCurrentDispatcher.current;
  if (dispatcher === null) {
    throw new Error(
      'react-cache: read and preload may only be called from within a ' +
        "component's render. They are not supported in event handlers or " +
        'lifecycle methods.',
    );
  }
  return dispatcher.readContext(Context, observedBits);
}

【讨论】：

【解决方案2】：

react-cache@2.0.0-alpha.1 的当前 alpha 版本与新发布的 react@16.8.0-alpha.0 和 react-dom@16.8.0-alpha.0 不兼容。

降级到react@16.7.0-alpha.1 和react-dom@16.7.0-alpha.1，直到发布新的兼容的react-cache alpha 版本。

【讨论】：

【解决方案3】：

我从网上找到的这个问题的解决方法是……

如果你只是想在开发环境中运行程序，你可以自己修改'react-cache/cjs/react-cache.development.js'中的代码：老：

    var currentOwner = React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED.ReactCurrentOwner;

    function readContext(Context, observedBits) {
        var dispatcher = currentOwner.currentDispatcher;
        if (dispatcher === null) {
        throw new Error('react-cache: read and preload may only be called from within a ' + "component's render. They are not supported in event handlers or " + 'lifecycle methods.');
       }
       return dispatcher.readContext(Context, observedBits);
     }

'currentOwner' 除了在函数 readContext 中没有用处。所以这是新的：

      var currentDispatcher =      React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED.ReactCurrentDispatcher;

     function readContext(Context, observedBits) {
          var dispatcher = currentDispatcher.current;
          if (dispatcher === null) {
               throw new Error('react-cache: read and preload may only be called from within a ' + "component's render. They are not supported in event handlers or " + 'lifecycle methods.');
           }
          return dispatcher.readContext(Context, observedBits);
         }

这在我的代码中有效。

【讨论】：