fetchDeferredAppLink returns undefined on iPhone 13 Promax (iOS 18.5) but returns a string value on iPhone 16 (iOS 26)

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Summary

The issue at hand is that the fetchDeferredAppLink function from the react-native-fbsdk-next library returns undefined on iPhone 13 Pro Max (iOS 18.5) but returns a string value on iPhone 16 (iOS 26). This discrepancy suggests a potential compatibility issue or a problem with the library’s handling of different iOS versions.

Root Cause

The root cause of this issue is likely related to the differences in how iOS 18.5 and iOS 26 handle App Tracking Transparency (ATT) and deferred deep links. The fetchDeferredAppLink function relies on the Facebook SDK’s ability to handle these features, which might be affected by changes in iOS versions.

Why This Happens in Real Systems

This issue occurs in real systems due to the following reasons:

  • iOS Version Differences: Variations in how different iOS versions implement and handle ATT and deferred deep links can lead to inconsistencies in the behavior of the Facebook SDK.
  • Library Compatibility: The react-native-fbsdk-next library might not be fully compatible with all iOS versions, especially if it doesn’t account for the specific changes and requirements introduced in different versions.
  • Device-Specific Factors: Device-specific factors, such as hardware or software configurations, could also influence how the library functions on different devices.

Real-World Impact

The real-world impact of this issue includes:

  • Inconsistent User Experience: Users on different devices or iOS versions might experience different behaviors when it comes to deep linking, which can lead to confusion and a negative user experience.
  • Difficulty in Tracking: The inability to reliably fetch deferred app links can make it challenging for developers to track the effectiveness of their marketing campaigns and understand user behavior.
  • Potential Loss of Data: If the fetchDeferredAppLink function fails to return a value, important data about the user’s interaction with the app might be lost, affecting analytics and decision-making.

Example or Code

const handleDeferredLink = async () => {
  try {
    const url = await AppLink.fetchDeferredAppLink();
    if (url) {
      console.log("FB: Success! Link received:", url);
      const params = extractParams(url);
      // Save the data and mark as handled
      await AsyncStorage.setItem('facebook_attribution', JSON.stringify(params));
      await AsyncStorage.setItem('fb_deferred_handled', 'true');
    } else {
      console.log("FB: No link found (Organic install or link expired).");
    }
  } catch (error) {
    console.error("FB: Error fetching deferred link:", error);
  }
};

How Senior Engineers Fix It

Senior engineers would approach this issue by:

  • Checking Library Documentation: Reviewing the react-native-fbsdk-next documentation to ensure they are using the latest version and following the recommended practices for handling deferred deep links.
  • Testing on Different Devices: Thoroughly testing the app on various devices and iOS versions to identify any patterns or specific conditions that might cause the issue.
  • Implementing Error Handling: Improving error handling to provide more detailed logs and insights into what might be causing the fetchDeferredAppLink function to return undefined.
  • Considering Workarounds: If the issue is due to a limitation or bug in the library, senior engineers might explore workarounds, such as using alternative methods for tracking deep links or implementing custom solutions.

Why Juniors Miss It

Junior engineers might miss this issue due to:

  • Lack of Experience: Inexperience with the specific library or iOS versions can lead to overlooking potential compatibility issues.
  • Insufficient Testing: Not thoroughly testing the app on different devices and iOS versions might mean the issue goes unnoticed until it’s reported by users.
  • Limited Understanding of ATT and Deferred Deep Links: A lack of deep understanding of how ATT and deferred deep links work, and how they are handled by different iOS versions, can make it difficult to identify and troubleshoot the issue.

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