Use file metadata with Cloud Storage on Flutter

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After uploading a file to Cloud Storage reference, you can also get and update the file metadata, for example to view or update the content type. Files can also store custom key/value pairs with additional file metadata.

Get File Metadata

File metadata contains common properties such as name, size, and contentType (often referred to as MIME type) in addition to some less common ones like contentDisposition and timeCreated. This metadata can be retrieved from a Cloud Storage reference using the getMetadata() method.

// Create reference to the file whose metadata we want to retrievefinalforestRef=storageRef.child("images/forest.jpg");// Get metadata propertiesfinalmetadata=awaitforestRef.getMetadata();// Metadata now contains the metadata for 'images/forest.jpg'

Update File Metadata

You can update file metadata at any time after the file upload completes by using the updateMetadata() method. Refer to the full list for more information on what properties can be updated. Only the properties specified in the metadata are updated, all others are left unmodified.

// Create reference to the file whose metadata we want to changefinalforestRef=storageRef.child("images/forest.jpg");// Create file metadata to updatefinalnewMetadata=SettableMetadata(cacheControl:"public,max-age=300",contentType:"image/jpeg",);// Update metadata propertiesfinalmetadata=awaitforestRef.updateMetadata(newMetadata);// Updated metadata for 'images/forest.jpg' is returned

You can delete writable metadata properties by passing null:

// Delete the cacheControl propertyfinalnewMetadata=SettableMetadata(cacheControl:null);finalmetadata=awaitforestRef.updateMetadata(newMetadata);

Handle Errors

There are a number of reasons why errors may occur on getting or updating metadata, including the file not existing, or the user not having permission to access the desired file. More information on errors can be found in the Handle Errors section of the docs.

Custom Metadata

You can specify custom metadata using the customMetadata parameter of the SettableMetadata constructor:

// Create reference to the file whose metadata we want to changefinalforestRef=storageRef.child("images/forest.jpg");// Create file metadata to updatefinalnewCustomMetadata=SettableMetadata(customMetadata:{"location":"Yosemite, CA, USA","activity":"Hiking",},);// Update metadata propertiesfinalmetadata=awaitforestRef.updateMetadata(newCustomMetadata);// Updated metadata for 'images/forest.jpg' is returned

You can store app-specific data for each file in custom metadata, but we highly recommend using a database (such as the Firebase Realtime Database) to store and synchronize this type of data.

File Metadata Properties

A full list of metadata properties on a file is available below:

Uploading, downloading, and updating files is important, but so is being able to remove them. Let's learn how to delete files from Cloud Storage.