自定义挂钩加载 Firebase 图片 URL

Question

I'm trying to create a custom hook that will load the URL for an image stored in Firebase.

So far I've arrived at the following:

useLoadImageURL.js

export default async function useLoadImageURL(projectId, fileName) {
    const [url, setURL] = useState()

    useEffect(() => {
        return url
    }, [url])

    const storage = getStorage(app);
    setURL(await getDownloadURL(ref(storage, `images/projects/${projectId}/${fileName}`)))
}

However, when I use it in my component, I only get promises, and therefore using the returned promise as URL does not work.

I'm calling the hook via the following:

ProjectCard.js

export default function ProjectCard({ project }) {
    const coverImageURL = useLoadImageURL(project.id, project.coverImagePath)
    return <img src={coverImageURL} />
}

How can I change the hook or how I'm calling it to retrieve the actual URL?

Answer 1

You can remove async and await from your code, and instead of calling setUrl at the bottom of your hook -- which would initiate the call every time the callee component rerenders -- wrap it in a useEffect , and update the state in a then callback.

edit: Full code:

const storage = getStorage(app); // as app seems to be external to the hook, storage can likely be too

export default function useLoadImageURL(projectId, fileName) {
  const [url, setUrl] = useState();

  useEffect(() => {
    getDownloadURL(ref(storage, `images/projects/${projectId}/${fileName}`))
      .then((value) => {
        setUrl(value); // should work provided getDownloadURL actually is a promise that gives a string
      });
  }, [projectId,fileName]);
  
  return url;
}

This will make the url state only change when projectId or fileName changes.

Answer 2

You have to do your side effect logic (awaiting async response in your case) inside the useEffect hook.

Following your intent to do it with promises and async await , your snippet hook should be something like this.

import { useState, useEffect } from "react";

// hook
function useLoadImageURL(filename) {
  const [url, setURL] = useState("some-image-spinner-url");

  // simulating your async api call to firebase service
  const setTimeoutAsync = (cb, delay) =>
    new Promise((resolve) => {
      setTimeout(() => {
        resolve(cb());
      }, delay);
    });

  useEffect(() => {
    async function asyncFn() {
      const url = await setTimeoutAsync(() => filename, 3000);
      setURL(url);
    }
    asyncFn();
  }, [filename]);

  return [url];
}

// main component
function App() {
  const [url] = useLoadImageURL("firebase-file-name-f1");
  return <div> {url} </div>;
}
export default App;