Your files are stored in a Cloud Storage bucket. The files in this bucket are presented in a hierarchical structure, just like the file system on your local hard disk, or the data in the Firebase Realtime Database . By creating a reference to a file, your app gains access to it. These references can then be used to upload or download data, get or update metadata or delete the file. A reference can either point to a specific file or to a higher level node in the hierarchy.
If you've used the Firebase Realtime Database , these paths should seem very familiar to you. However, your file data is stored in Cloud Storage , notin the Realtime Database .
Create a Reference
Create a reference to upload, download, or delete a file, or to get or update its metadata. A reference can be thought of as a pointer to a file in the cloud. References are lightweight, so you can create as many as you need. They are also reusable for multiple operations.
References are created from the Firebase.Storage.FirebaseStorage
service on
your Firebase app by calling the GetReferenceFromUrl()
method and passing in a
URL of the form gs://<your-cloud-storage-bucket>
. You can find this URL in
the Storage section
of the Firebase
console
.
// Get a reference to the storage service, using the default Firebase App FirebaseStorage storage = FirebaseStorage . DefaultInstance ; // Create a storage reference from our storage service StorageReference storageRef = storage . GetReferenceFromUrl ( "gs://<your-cloud-storage-bucket>" );
You can create a reference to a location lower in the tree, for example 'images/space.jpg'
, by using the child
method on an existing reference.
// Create a child reference // imagesRef now points to "images" StorageReference imagesRef = storageRef . Child ( "images" ); // Child references can also take paths delimited by '/' such as: // "images/space.jpg". StorageReference spaceRef = imagesRef . Child ( "space.jpg" ); // spaceRef now points to "images/space.jpg" // imagesRef still points to "images" // This is equivalent to creating the full referenced StorageReference spaceRefFull = storage . GetReferenceFromUrl ( "gs://<your-cloud-storage-bucket>/images/space.jpg" );
Navigate with References
You can also use the Parent
and Root
methods to navigate up in our file
hierarchy. Parent
navigates up one level, while Root
navigates all the way
to the top.
// Parent allows us to move to the parent of a reference // imagesRef now points to 'images' StorageReference imagesRef = spaceRef . Parent ; // Root allows us to move all the way back to the top of our bucket // rootRef now points to the root StorageReference rootRef = spaceRef . Root ;
Child
, Parent
, and Root
can be chained together multiple times, as
each returns a reference. The exception is the Parent
of Root
, which
is an invalid StorageReference
.
// References can be chained together multiple times // earthRef points to "images/earth.jpg" StorageReference earthRef = spaceRef . Parent . Child ( "earth.jpg" ); // nullRef is null since the parent of root is an invalid StorageReference StorageReference nullRef = spaceRef . Root . Parent ;
Reference Methods
You can inspect references to better understand the files they point to using
the Path
, Name
, and Bucket
properties. These properties get the file's
full path, name, and bucket.
// Reference's path is: "images/space.jpg" // This is analogous to a file path on disk string path = spaceRef . Path ; // Reference's name is the last segment of the full path: "space.jpg" // This is analogous to the file name string name = spaceRef . Name ; // Reference's bucket is the name of the storage bucket where files are stored string bucket = spaceRef . Bucket ;
Limitations on References
Reference paths and names can contain any sequence of valid Unicode characters, but certain restrictions are imposed including:
- Total length of
reference.Pathmust be between 1 and 1024 bytes when UTF-8 encoded. - No Carriage Return or Line Feed characters.
- Avoid using
#,[,],*, or?, as these do not work well with other tools such as the Firebase Realtime Database or gsutil .
Full Example
FirebaseStorage storage = FirebaseStorage . DefaultInstance ; // Points to the root reference StorageReference storageRef = storage . GetReferenceFromUrl ( "gs://<your-bucket-name>" ); // Points to "images" StorageReference imagesRef = storageRef . Child ( "images" ); // Points to "images/space.jpg" // Note that you can use variables to create child values string filename = "space.jpg" ; StorageReference spaceRef = imagesRef . Child ( filename ); // File path is "images/space.jpg" string path = spaceRef . Path ; // File name is "space.jpg" string name = spaceRef . Name ; // Points to "images" StorageReference imagesRef = spaceRef . Parent ;
Next Steps
Next, let's learn how to upload files to Cloud Storage .
