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
calling its
getReference()
method.
Kotlin+KTX
// Create a storage reference from our app
var storageRef = storage.reference
Java
// Create a storage reference from our app
StorageReference storageRef = storage.getReference();
Next, you can create a reference to a location lower in the tree,
say
"images/space.jpg"
by using the
child()
method on an existing reference.
Kotlin+KTX
// Create a child reference
// imagesRef now points to "images"
var imagesRef: StorageReference? = storageRef.child("images")
// Child references can also take paths
// spaceRef now points to "images/space.jpg
// imagesRef still points to "images"
var spaceRef = storageRef.child("images/space.jpg")
Java
// Create a child reference
// imagesRef now points to "images"
StorageReference imagesRef = storageRef.child("images");
// Child references can also take paths
// spaceRef now points to "images/space.jpg
// imagesRef still points to "images"
StorageReference spaceRef = storageRef.child("images/space.jpg");
Navigate with References
You can also use the
getParent()
and
getRoot()
methods to navigate up in our
file hierarchy.
getParent()
navigates up one level,
while
getRoot()
navigates all the way to the top.
Kotlin+KTX
// parent allows us to move our reference to a parent node
// imagesRef now points to 'images'
imagesRef = spaceRef.parent
// root allows us to move all the way back to the top of our bucket
// rootRef now points to the root
val rootRef = spaceRef.root
Java
// getParent allows us to move our reference to a parent node
// imagesRef now points to 'images'
imagesRef = spaceRef.getParent();
// getRoot allows us to move all the way back to the top of our bucket
// rootRef now points to the root
StorageReference rootRef = spaceRef.getRoot();
child()
,
getParent()
, and
getRoot()
can be chained together multiple
times, as each returns a reference. But calling
getRoot().getParent()
returns
null
.
Kotlin+KTX
// References can be chained together multiple times
// earthRef points to 'images/earth.jpg'
val earthRef = spaceRef.parent?.child("earth.jpg")
// nullRef is null, since the parent of root is null
val nullRef = spaceRef.root.parent
Java
// References can be chained together multiple times
// earthRef points to 'images/earth.jpg'
StorageReference earthRef = spaceRef.getParent().child("earth.jpg");
// nullRef is null, since the parent of root is null
StorageReference nullRef = spaceRef.getRoot().getParent();
Reference Properties
You can inspect references to better understand the files they point to
using the
getPath()
,
getName()
, and
getBucket()
methods. These methods
get the file's full path, name and bucket.
Kotlin+KTX
// Reference's path is: "images/space.jpg"
// This is analogous to a file path on disk
spaceRef.path
// 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
Java
// Reference's path is: "images/space.jpg"
// This is analogous to a file path on disk
spaceRef.getPath();
// Reference's name is the last segment of the full path: "space.jpg"
// This is analogous to the file name
spaceRef.getName();
// Reference's bucket is the name of the storage bucket that the files are stored in
spaceRef.getBucket();
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
#
,
[
,
]
,
*
, or
?
, as these do not work well with
other tools such as the
Firebase Realtime Database
or
gsutil
.
Full Example
Kotlin+KTX
// Points to the root reference
storageRef = storage.reference
// Points to "images"
imagesRef = storageRef.child("images")
// Points to "images/space.jpg"
// Note that you can use variables to create child values
val fileName = "space.jpg"
spaceRef = imagesRef.child(fileName)
// File path is "images/space.jpg"
val path = spaceRef.path
// File name is "space.jpg"
val name = spaceRef.name
// Points to "images"
imagesRef = spaceRef.parent
Java
// Points to the root reference
storageRef = storage.getReference();
// Points to "images"
imagesRef = storageRef.child("images");
// Points to "images/space.jpg"
// Note that you can use variables to create child values
String fileName = "space.jpg";
spaceRef = imagesRef.child(fileName);
// File path is "images/space.jpg"
String path = spaceRef.getPath();
// File name is "space.jpg"
String name = spaceRef.getName();
// Points to "images"
imagesRef = spaceRef.getParent();
Next, let's learn how to
upload files
to
Cloud Storage.