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Configuring useReadContract

The useReadContract hook has a number of configurable properties that will allow you to adapt it to your needs. You can combine the functionality of TanStack queries with useBlockNumber to watch the blockchain for changes, although doing so will consume a number of API calls.

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Objectives

By the end of this guide you should be able to:
  • Use useBlockNumber and the queryClient to automatically fetch updates from the blockchain
  • Describe the costs of using the above, and methods to reduce those costs
  • Configure arguments to be passed with a call to a pure or view smart contract function
  • Call an instance of useReadContract on demand
  • Utilize isLoading and isFetching to improve user experience

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Fetching Updates from the Blockchain

You’ll continue with the project you’ve been building and last updated while learning about the useReadContract hook. Once the excitement of your accomplishment of finally reading from your own contract subsides, try using BaseScan to add another issue, or vote on an existing issue. You’ll notice that your frontend does not update. There are a few ways to handle this.
1

Fetch updates from the blockchain

Use useBlockNumber with the watch feature to automatically keep track of the block number, then use the queryClient to update when that changes. Make sure you decompose the queryKey from the return of useReadContract.
import { useEffect, useState } from 'react';
import { useReadContract, useBlockNumber } from 'wagmi';
import { useQueryClient } from '@tanstack/react-query';

// Other Code

export function IssueList() {
  // Other Code

  const queryClient = useQueryClient();
  const { data: blockNumber } = useBlockNumber({ watch: true });

  const {
    data: issuesData,
    isError: issuesIsError,
    isPending: issuesIsPending,
    queryKey: issuesQueryKey,
  } = useReadContract({
    address: contractData.address as `0x${string}`,
    abi: contractData.abi,
    functionName: 'getAllIssues',
  });

  useEffect(() => {
    queryClient.invalidateQueries({ queryKey: issuesQueryKey });
  }, [blockNumber, queryClient, issuesQueryKey]);

  // Return code
}
Don’t do this, either use multi-call via useReadContracts, or consolidate your views into a single function that fetches all the data you need in one call.
2

Pause on blur

Stop watching the blockchain if the website doesn’t have focus. Add a state variable to count how many times the function has settled, and one for if the page is focused. Set up event listeners to set the state of the latter when the page is focused or blurred.
const [timesCalled, setTimesCalled] = useState(0);
const [pageIsFocused, setPageIsFocused] = useState(true);

useEffect(() => {
  const onFocus = () => setPageIsFocused(true);
  const onBlur = () => setPageIsFocused(false);

  window.addEventListener('focus', onFocus);
  window.addEventListener('blur', onBlur);

  return () => {
    window.removeEventListener('focus', onFocus);
    window.removeEventListener('blur', onBlur);
  };
}, []);
Update the watch for useBlockNumber so that it only does so if pageIsFocused.
const { data: blockNumber } = useBlockNumber({ watch: pageIsFocused });
Add a line to the useEffect for blockNumber and increment your counter as well.
useEffect(() => {
  setTimesCalled((prev) => prev + 1);
  queryClient.invalidateQueries({ queryKey: issuesQueryKey });
}, [blockNumber, queryClient]);
Finally, surface your counter in the component.
return (
  <div>
    <h2>Number of times called</h2>
    <p>{timesCalled.toString()}</p>
    <p>{'Has focus: ' + pageIsFocused}</p>
    <h2>All Issues</h2>
    <div>{renderIssues()}</div>
  </div>
);
3

Adjust the polling rate

Adjust your pollingInterval by setting it in getDefaultConfig in _app.tsx:
const config = getDefaultConfig({
  appName: 'RainbowKit App',
  projectId: 'YOUR_PROJECT_ID',
  chains: [baseSepolia],
  ssr: true,
  pollingInterval: 30_000,
});
Setting it to 30 seconds, or 30,000 milliseconds, will reduce your API calls dramatically, without negatively impacting members of the DAO.
4

Update on demand

Use a similar system to call your update function on demand. Add a button, a handler for that button, and a state variable for it to set:
const [triggerRead, setTriggerRead] = useState(false);

const handleTriggerRead = () => {
  setTriggerRead(true);
};

return (
  <div>
    <button onClick={handleTriggerRead}>Read Now</button>
    <h2>Number of times called</h2>
    <p>{timesCalled.toString()}</p>
    <p>{'Has focus: ' + pageIsFocused}</p>
    <h2>All Issues</h2>
    <div>{renderIssues()}</div>
  </div>
);
Finally, set watch to equal triggerRead, instead of pageIsFocused, and reset triggerRead in the useEffect.
const { data: blockNumber } = useBlockNumber({ watch: triggerRead });

// Other code...

useEffect(() => {
  setTriggerRead(false);
  queryClient.invalidateQueries({ queryKey: issuesQueryKey });
}, [blockNumber, queryClient]);
5

Set UI elements based on status

Use the “is” return values to set UI elements depending on the status of the hook as it attempts to call a function on the blockchain.
<button disabled={issuesIsFetching} onClick={handleTriggerRead}>
  {issuesIsFetching ? 'Loading' : 'Read Now'}
</button>
You’ll probably see the button flicker very quickly since the call doesn’t take very long. For a production app, you’d need to add additional handling to smooth out the experience.
6

Pass arguments to useReadContract

Arguments are passed into a useReadContract hook by adding an array of arguments, in order, to the args property. Common practice is to use React state variables set by UI elements to enable the arguments to be set and modified. For example, you might create a drop-down to set issueNumber, then fetch that issue with:
const [issueNumber, setIssueNumber] = useState(0);

const { isLoading: getIssueIsLoading } = useReadContract({
  address: contractData.address as `0x${string}`,
  abi: contractData.abi,
  functionName: 'getIssue',
  args: [issueNumber],
});

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Conclusion

In this guide, you’ve learned how to use the watch feature of useBlockNumber combined with useEffect and queryClient.invalidateQueries to enable your frontend to see updates to your smart contract. You’ve also learned the costs of doing so, and some strategies for mitigation. You’ve learned how to pass arguments to your functions. Finally, you’ve learned how to use the properties returned by useReadContract to adjust your UI to improve the experience for your users.
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