如何让Gmail Add-On的onTriggerFunction每次打开邮件都执行？

Hey there, I’ve dealt with this exact caching quirk in Gmail Add-Ons before—let’s break down how to make your onTriggerFunction fire every time a user opens an email, instead of just the first time.

First, the root issue: Gmail caches the initial card response from your trigger function to speed up load times. When you switch back to an email you’ve already opened, it pulls that cached card instead of re-running your logic. But we can override this behavior with a simple card configuration change.

Solution 1: Disable Card Caching (Automatic Refresh) #

The most straightforward fix is to tell Gmail not to cache your card at all. You can do this by adding setCachePolicy(CardService.CachePolicy.NO_CACHE) when building your card.

Here’s how to update your Code.js example:

function buildAddOn(e) { 
  var card = CardService.newCardBuilder(); 
  card.setHeader(CardService.newCardHeader().setTitle(new Date().toLocaleTimeString()))
      // This line disables caching entirely
      .setCachePolicy(CardService.CachePolicy.NO_CACHE); 
  return [card.build()]; 
}

With this change, every time a user opens the email (even if they’ve opened it before), Gmail will re-call buildAddOn and load the latest card content—perfect for your dynamic time example or any business logic that needs fresh data.

Solution 2: Add a Manual Refresh Button (Optional) #

If you want to keep some caching for performance but give users a way to refresh manually, you can add a refresh action to your card header. This lets users trigger a re-run of onTriggerFunction with a click.

Update your code like this:

function buildAddOn(e) {
  // Create an action that re-runs your build function
  var refreshAction = CardService.newAction()
      .setFunctionName("buildAddOn")
      .setLoadIndicator(CardService.LoadIndicator.SPINNER);
  
  // Add a refresh icon to the card header that triggers the action
  var header = CardService.newCardHeader()
      .setTitle(new Date().toLocaleTimeString())
      .setImageUrl("https://www.gstatic.com/images/icons/material/system/2x/refresh_black_24dp.png")
      .setImageAction(refreshAction);
  
  var card = CardService.newCardBuilder()
      .setHeader(header);
  
  return [card.build()];
}

This gives users control over when to refresh, which can be a good middle ground if automatic refreshes aren’t strictly necessary for every use case.

Why Does This Happen? #

Gmail’s default caching is a performance optimization—cutting down on server calls makes Add-Ons feel faster. But for dynamic content (like real-time timestamps or context-dependent business logic), this optimization gets in the way. Disabling the cache tells Gmail that your card content needs to be fresh every time.

内容的提问来源于stack exchange，提问作者user458729