函数会在 React 中获取最新的状态值吗？

Question

I have a function inside of my functional component that uses a value saved in state. However, when it is called, it has the original value in state, not the updated value. When I look at my component in Chrome React Dev Tools, I see that the updated value is stored in state. Aren't functions supposed to get the latest state value in React? I didn't think I'd have to wrap my functions in a useEffect every time some value in state they depend on changes. Why is this happening?

const Editor = (props) => {
  const [template, setTemplate] = useState(null);
  const [openDialog, setOpenDialog] = useState(false);

  useEffect(() => {
   if (props.templateId) {
     getTemplate(props.templateId));
   }
  },[]);

  const getTemplate = (templateId) => {
    {...make API to get template...}
    .then((response) => {
      if (response.template) setTemplate(response.template);
    });
  }

  /* THIS FUNCTION SAYS TEMPLATE IS ALWAYS NULL */
  const sendClick = async () => {
    if (template) {
      await updateTemplate();
    } else {
      await initializeTemplate();
    }
    setOpenDialog(true);
  };

}

UPDATE: I figured out the issue. The sendClick function is being used inside an object that I have in state. When that object is created, it creates a version of the sendClick function based on the state at that time. I realized I needed to refactor my code so that the function is not stored within my object in state so that the function will always have the latest state values.

Answer 1

Please correct the code there its setTemplate(template)); not getTemplate(template)); I'm guessing that you have that right in the source code... if Yes then,

You have got into a trap that all developers new to React fall into.

This code is betraying you ...

 useEffect(() => {
   if (props.template) {
     setTemplate(template)); // Mentioned as getTemplate(template));
   }
  },[]); // Here is where you make the mistake

The second argument you pass to the useEffect is called as Dependencies . Meaning if your useEffect is dependent on any state or any variable or function, Ii should be pass as the second argument inside the [] . By now you should have got the answer.

Clearly, your useEffect is dependent on template . You should pass that inside the [] .

So the code will be : -

 useEffect(() => {
   if (props.template) {
     setTemplate(template)); // Mentioned as getTemplate(template));
   }
  },[template]);

Now React will automatically run the function every time the value of template changes therefore, updates template .

For more information about useEffect ...

Refer React Documentation

Refer the useEffect API