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, not in 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.
Create a reference using the
FirebaseStorage singleton instance and
final storageRef = FirebaseStorage.instance.ref();
Next, you can create a reference to a location lower in the tree,
"images/space.jpg" by using the
child() method on an existing reference.
// Create a child reference // imagesRef now points to "images" final imagesRef = storageRef.child("images"); // Child references can also take paths // spaceRef now points to "images/space.jpg // imagesRef still points to "images" final spaceRef = storageRef.child("images/space.jpg");
Navigate with References
You can also use the
root properties to navigate up in our
parent navigates up one level,
root navigates all the way to the top.
// parent allows us to move our reference to a parent node // imagesRef2 now points to 'images' final imagesRef2 = spaceRef.parent; // root allows us to move all the way back to the top of our bucket // rootRef now points to the root final rootRef = spaceRef.root;
root can be chained together multiple
times, as each is a reference. But accessing
root.parent results in
// References can be chained together multiple times // earthRef points to 'images/earth.jpg' final earthRef = spaceRef.parent?.child("earth.jpg"); // nullRef is null, since the parent of root is null final nullRef = spaceRef.root.parent;
You can inspect references to better understand the files they point to
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 spaceRef.fullPath; // Reference's name is the last segment of the full path: "space.jpg" // This is analogous to the file name spaceRef.name; // Reference's bucket is the name of the storage bucket that the files are stored in 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.fullPath must be between 1 and 1024 bytes when UTF-8 encoded.
- No Carriage Return or Line Feed characters.
- Avoid using
?, as these do not work well with other tools such as the Firebase Realtime Database or gsutil.
// Points to the root reference final storageRef = FirebaseStorage.instance.ref(); // Points to "images" Reference? imagesRef = storageRef.child("images"); // Points to "images/space.jpg" // Note that you can use variables to create child values final fileName = "space.jpg"; final spaceRef = imagesRef.child(fileName); // File path is "images/space.jpg" final path = spaceRef.fullPath; // File name is "space.jpg" final name = spaceRef.name; // Points to "images" imagesRef = spaceRef.parent;
Next, let's learn how to upload files to Cloud Storage.