Understanding StreamBuilder in Flutter: Fixing DocumentSnapshot Issues

Описание: Explore how to troubleshoot `StreamBuilder DocumentSnapshot ` in Flutter to dynamically show icons based on survey completion status.
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This video is based on the question https://stackoverflow.com/q/62252972/ asked by the user 'David' ( https://stackoverflow.com/u/13385865/ ) and on the answer https://stackoverflow.com/a/62283060/ provided by the user 'David' ( https://stackoverflow.com/u/13385865/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding StreamBuilder in Flutter: Fixing DocumentSnapshot Issues

In Flutter development, the StreamBuilder is an essential widget that listens to streams and builds its children based on the latest snapshot of interaction with the stream. However, developers may encounter issues when working with Firestore, especially when trying to assess the existence of documents in the database. A common problem arises when checking the validity of data received from a StreamBuilder<DocumentSnapshot> in Firestore.

The Problem at Hand

You might find yourself in a scenario where you need to display different icons based on whether a user has completed a survey. You are using StreamBuilder to listen for changes to a specific document in Firestore, and based on the returned survey name, you want to connect with another collection to determine if the survey has been completed by the user.

However, a typical issue arises: even if the survey document does not exist, the snapshot appears to have data, causing the app to incorrectly show the check icon.

What's Going Wrong?

The confusion stems from how Firestore manages DocumentSnapshots. Even if a document doesn't exist, the DocumentSnapshot object is returned but does not contain any data. If you're checking for data simply by using snapshot.hasData, it can lead to misleading results.

The Solution

To correctly determine whether the document exists in Firestore and to display the icons appropriately, you can utilize snapshot1.data.exists. Below is a corrected version of the code snippet that addresses this issue.

Revised Code

[[See Video to Reveal this Text or Code Snippet]]

Key Changes Explained

Existence Check: Instead of relying on snapshot1.hasData, which may incorrectly indicate that a document exists, we use snapshot1.data.exists. This explicitly checks if the document with the user ID in the survey entrants collection actually exists.

Icon Presentation: Based on the existence of the document, you show different icons:

A burst icon if data is still loading.

A check icon if the survey has been completed.

An error outline icon if the survey document does not exist.

Conclusion

By reviewing the way you check for document existence in StreamBuilder<DocumentSnapshot>, you can avoid common pitfalls in displaying data from Firestore. The adjustment to check for exists ensures that your UI accurately reflects the user’s survey status, enhancing overall user experience and application reliability.

Next time you're working with StreamBuilders in Flutter, remember this crucial tip to keep your conditional rendering accurate!