Cloud Storage for Firebase allows you to quickly and easily download files from a Cloud Storage bucket provided and managed by Firebase.
Create a Reference
To download a file, first create a Cloud Storage reference to the file you want to download.
You can create a reference by appending child paths to the root of your
Cloud Storage bucket, or you can create a reference from an existing gs://
or https://
URL referencing an object in Cloud Storage.
// Create a storage reference from our app
final
storageRef
=
FirebaseStorage
.
instance
.
ref
();
// Create a reference with an initial file path and name
final
pathReference
=
storageRef
.
child
(
"images/stars.jpg"
);
// Create a reference to a file from a Google Cloud Storage URI
final
gsReference
=
FirebaseStorage
.
instance
.
refFromURL
(
"gs://YOUR_BUCKET/images/stars.jpg"
);
// Create a reference from an HTTPS URL
// Note that in the URL, characters are URL escaped!
final
httpsReference
=
FirebaseStorage
.
instance
.
refFromURL
(
"https://firebasestorage.googleapis.com/b/YOUR_BUCKET/o/images%20stars.jpg"
);
Download Files
Once you have a reference, you can download files from Cloud Storage
by calling the getData()
. If you prefer to download the file
with another library, you can get a download URL with getDownloadUrl()
.
Download in memory
Download the file to a UInt8List
with the getData()
method. This is the
easiest way to download a file, but it must load the entire contents of
your file into memory. If you request a file larger than your app's available
memory, your app will crash. To protect against memory issues, getData()
takes a maximum amount of bytes to download. Set the maximum size to something
you know your app can handle, or use another download method.
final
islandRef
=
storageRef
.
child
(
"images/island.jpg"
);
try
{
const
oneMegabyte
=
1024
*
1024
;
final
Uint8List
?
data
=
await
islandRef
.
getData
(
oneMegabyte
);
// Data for "images/island.jpg" is returned, use this as needed.
}
on
FirebaseException
catch
(
e
)
{
// Handle any errors.
}
Download to a local file
The writeToFile()
method downloads a file directly to a local device. Use this if
your users want to have access to the file while offline or to share the file in a
different app. writeToFile()
returns a DownloadTask
which you can use to manage
your download and monitor the status of the download.
final
islandRef
=
storageRef
.
child
(
"images/island.jpg"
);
final
appDocDir
=
await
getApplicationDocumentsDirectory
();
final
filePath
=
"
${
appDocDir
.
absolute
}
/images/island.jpg"
;
final
file
=
File
(
filePath
);
final
downloadTask
=
islandRef
.
writeToFile
(
file
);
downloadTask
.
snapshotEvents
.
listen
((
taskSnapshot
)
{
switch
(
taskSnapshot
.
state
)
{
case
TaskState
.
running:
// TODO: Handle this case.
break
;
case
TaskState
.
paused:
// TODO: Handle this case.
break
;
case
TaskState
.
success:
// TODO: Handle this case.
break
;
case
TaskState
.
canceled:
// TODO: Handle this case.
break
;
case
TaskState
.
error:
// TODO: Handle this case.
break
;
}
});
Download Data via URL
If you already have download infrastructure based around URLs, or just want
a URL to share, you can get the download URL for a file by calling the getDownloadURL()
method on a Cloud Storage reference.
final
imageUrl
=
await
storageRef
.
child
(
"users/me/profile.png"
).
getDownloadURL
();
Handle Errors
There are a number of reasons why errors may occur on download, 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.
Full Example
A full example of a download with error handling is shown below:
final
islandRef
=
storageRef
.
child
(
"images/island.jpg"
);
final
appDocDir
=
await
getApplicationDocumentsDirectory
();
final
filePath
=
"
${
appDocDir
.
absolute
}
/images/island.jpg"
;
final
file
=
File
(
filePath
);
final
downloadTask
=
islandRef
.
writeToFile
(
file
);
downloadTask
.
snapshotEvents
.
listen
((
taskSnapshot
)
{
switch
(
taskSnapshot
.
state
)
{
case
TaskState
.
running:
// TODO: Handle this case.
break
;
case
TaskState
.
paused:
// TODO: Handle this case.
break
;
case
TaskState
.
success:
// TODO: Handle this case.
break
;
case
TaskState
.
canceled:
// TODO: Handle this case.
break
;
case
TaskState
.
error:
// TODO: Handle this case.
break
;
}
});
You can also get and update metadata for files that are stored in Cloud Storage.
