如何在react (Hooks)中更新值而不是重新渲染完整的应用程序？

Question

在这里，我尝试使用Context-API将header组件的值更新为search组件。在我的例子中，我在header组件中有一个dropdown，我希望将dropdown值传递给搜索页面，而不重新呈现搜索组件。下面是我的示例代码

​

import React,{useContext,useState} from "react";
import { RepoContext } from "../../App";

const App = ()=>{
   const [RepoUrn, setRepoUrn] = useState("");
   const handleRepo = (value) => {  // Callback from Header to update the dropdown value and I am sending this context so the state is updated and rendering mutliple times 
    return setRepoUrn(value);
  };
}
const Search =()=>{
   const context = useContext(RepoContext);
  console.log(context);

   React.useEffect(()=>{
     console.log('context',context) -> Found here re rendering multiple times
   },[context]);
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.4.2/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.4.2/umd/react-dom.production.min.js"></script>
**APP.js**
<RepoContext.Provider value={RepoUrn}>
        <div className="app">
          <>
            <Header
              
              locale={locale}
              repoValues={RepoValues}
              setLocale={setLocale}
              onSelectRepo={handleRepo}
            />
     <Route path="/" component={Search} />
     </>
 </RepoContext.Provider>
 
 **Header.js**
<Dropdown isOpen={repoOpen} toggle={(e) => toggle(e, "Repo")}>
<DropdownToggle
   tag="span"
  data-toggle="dropdown"
  aria-expanded={repoOpen}
  data-value={dataUrn}
  id="test"
>
  {TruncateMessage(RepoValue)}
  <img src={downarrow} className="downarrow" />
</DropdownToggle>
  <DropdownMenu
    style={dropDownStyles}
    id="scroll_styles"
    onClick={(e) => changeDropdownValue(e, "Repo")}
  >
    {props.repoValues.length > 0
      ? props.repoValues.map((item, index) => {
          return (
            <div
              key={index}
              className="subMenu"
              data-value={item.urn}
              data-shows={item.name}
            >
              <h6>{item.name}</h6>
            </div>
          );
        })
      : ""}
  </DropdownMenu>
</Dropdown>

How can I pass dropdown value from header to context and subscribe in search without search component re rendering even if I get the new value from header?

​

Answer 1

在定义Context的值时，您需要定义值和回调函数来更改该值。我认为你应该阅读并遵循这个react文档https://reactjs.org/docs/context.html#updating-context-from-a-nested-component