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
.
Swift
// Create a reference with an initial file path and name let pathReference = storage . reference ( withPath : "images/stars.jpg" ) // Create a reference from a Google Cloud Storage URI let gsReference = storage . reference ( forURL : "gs://<your-firebase-storage-bucket>/images/stars.jpg" ) // Create a reference from an HTTPS URL // Note that in the URL, characters are URL escaped! let httpsReference = storage . reference ( forURL : "https://firebasestorage.googleapis.com/b/bucket/o/images%20stars.jpg" )
Objective-C
// Create a reference with an initial file path and name FIRStorageReference * pathReference = [ storage referenceWithPath : @"images/stars.jpg" ]; // Create a reference from a Google Cloud Storage URI FIRStorageReference * gsReference = [ storage referenceForURL : @"gs://<your-firebase-storage-bucket>/images/stars.jpg" ]; // Create a reference from an HTTPS URL // Note that in the URL, characters are URL escaped! FIRStorageReference * httpsReference = [ storage referenceForURL : @"https://firebasestorage.googleapis.com/b/bucket/o/images%20stars.jpg" ];
Download Files
Once you have a reference, you can download files from Cloud Storage in three ways:
- Download to
NSDatain memory - Download to an
NSURLrepresenting a file on device - Generate an
NSURLrepresenting the file online
Download in memory
Download the file to an NSData
object in memory using the dataWithMaxSize:completion:
method. This is the easiest way to quickly
download a file, but it must load 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, make sure to set the max size
to something you know your app can handle, or use another
download method.
Swift
// Create a reference to the file you want to download let islandRef = storageRef . child ( "images/island.jpg" ) // Download in memory with a maximum allowed size of 1MB (1 * 1024 * 1024 bytes) islandRef . getData ( maxSize : 1 * 1024 * 1024 ) { data , error in if let error = error { // Uh-oh, an error occurred! } else { // Data for "images/island.jpg" is returned let image = UIImage ( data : data !) } }
Objective-C
// Create a reference to the file you want to download FIRStorageReference * islandRef = [ storageRef child : @"images/island.jpg" ]; // Download in memory with a maximum allowed size of 1MB (1 * 1024 * 1024 bytes) [ islandRef dataWithMaxSize : 1 * 1024 * 1024 completion :^ ( NSData * data , NSError * error ){ if ( error != nil ) { // Uh-oh, an error occurred! } else { // Data for "images/island.jpg" is returned UIImage * islandImage = [ UIImage imageWithData : data ]; } }];
Download to a local file
The writeToFile:completion:
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 in a different app. writeToFile:completion:
returns an FIRStorageDownloadTask
which you can use to manage your download and monitor
the status of the upload.
Swift
// Create a reference to the file you want to download let islandRef = storageRef . child ( "images/island.jpg" ) // Create local filesystem URL let localURL = URL ( string : "path/to/image" ) ! // Download to the local filesystem let downloadTask = islandRef . write ( toFile : localURL ) { url , error in if let error = error { // Uh-oh, an error occurred! } else { // Local file URL for "images/island.jpg" is returned } }
Objective-C
// Create a reference to the file you want to download FIRStorageReference * islandRef = [ storageRef child : @"images/island.jpg" ]; // Create local filesystem URL NSURL * localURL = [ NSURL URLWithString : @"path/to/image" ]; // Download to the local filesystem FIRStorageDownloadTask * downloadTask = [ islandRef writeToFile : localURL completion :^ ( NSURL * URL , NSError * error ){ if ( error != nil ) { // Uh-oh, an error occurred! } else { // Local file URL for "images/island.jpg" is returned } }];
If you want to actively manage your download, you can use the writeToFile:
method and observe the download task, rather than use the completion handler.
See Manage Downloads
for more information.
Generate a download 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 downloadURLWithCompletion:
method on a Cloud Storage
reference.
Swift
// Create a reference to the file you want to download let starsRef = storageRef . child ( "images/stars.jpg" ) // Fetch the download URL starsRef . downloadURL { url , error in if let error = error { // Handle any errors } else { // Get the download URL for 'images/stars.jpg' } }
Objective-C
// Create a reference to the file you want to download FIRStorageReference * starsRef = [ storageRef child : @"images/stars.jpg" ]; // Fetch the download URL [ starsRef downloadURLWithCompletion :^ ( NSURL * URL , NSError * error ){ if ( error != nil ) { // Handle any errors } else { // Get the download URL for 'images/stars.jpg' } }];
Downloading Images with FirebaseUI
FirebaseUI provides simple, customizable, and production-ready native mobile bindings to eliminate boilerplate code and promote Google best practices. Using FirebaseUI you can quickly and easily download, cache, and display images from Cloud Storage using our integration with SDWebImage .
First, add FirebaseUI to your Podfile
:
pod 'FirebaseStorageUI'
Then you can load images directly from Cloud Storage
into a UIImageView
:
Swift
// Reference to an image file in Firebase Storage let reference = storageRef . child ( "images/stars.jpg" ) // UIImageView in your ViewController let imageView : UIImageView = self . imageView // Placeholder image let placeholderImage = UIImage ( named : "placeholder.jpg" ) // Load the image using SDWebImage imageView . sd_setImage ( with : reference , placeholderImage : placeholderImage )
Objective-C
// Reference to an image file in Firebase Storage FIRStorageReference * reference = [ storageRef child : @"images/stars.jpg" ]; // UIImageView in your ViewController UIImageView * imageView = self . imageView ; // Placeholder image UIImage * placeholderImage ; // Load the image using SDWebImage [ imageView sd_setImageWithStorageReference : reference placeholderImage : placeholderImage ];
Manage Downloads
In addition to starting downloads, you can pause, resume, and cancel downloads
using the pause
, resume
, and cancel
methods. These methods raise pause
, resume
, and cancel
events that you can observe.
Swift
// Start downloading a file let downloadTask = storageRef . child ( "images/mountains.jpg" ). write ( toFile : localFile ) // Pause the download downloadTask . pause () // Resume the download downloadTask . resume () // Cancel the download downloadTask . cancel ()
Objective-C
// Start downloading a file FIRStorageDownloadTask * downloadTask = [[ storageRef child : @"images/mountains.jpg" ] writeToFile : localFile ]; // Pause the download [ downloadTask pause ]; // Resume the download [ downloadTask resume ]; // Cancel the download [ downloadTask cancel ];
Monitor Download Progress
You can attach observers to FIRStorageDownloadTask
s in order to monitor the
progress of the download. Adding an observer returns a FIRStorageHandle
that can be used to remove the observer.
Swift
// Add a progress observer to a download task let observer = downloadTask . observe (. progress ) { snapshot in // A progress event occurred }
Objective-C
// Add a progress observer to a download task NSString * observer = [ downloadTask observeStatus : FIRStorageTaskStatusProgress handler : ^ ( FIRStorageTaskSnapshot * snapshot ) { // A progress event occurred }];
These observers can be registered to an FIRStorageTaskStatus
event:
| `FIRStorageTaskStatus` Event | Typical Usage |
|---|---|
FIRStorageTaskStatusResume
|
This event fires when the task starts or resumes downloading, and is
often used in conjunction with the FIRStorageTaskStatusPause
event. |
FIRStorageTaskStatusProgress
|
This event fires any time data is downloaded from Cloud Storage , and can be used to populate a download progress indicator. |
FIRStorageTaskStatusPause
|
This event fires any time the download is paused, and is often used in
conjunction with the FIRStorageTaskStatusResume
event. |
FIRStorageTaskStatusSuccess
|
This event fires when a download has completed successfully. |
FIRStorageTaskStatusFailure
|
This event fires when a download has failed. Inspect the error to determine the failure reason. |
When an event occurs, an FIRStorageTaskSnapshot
object is passed back. This
snapshot is an immutable view of the task, at the time the event occurred.
This object contains the following properties:
| Property | Type | Description |
|---|---|---|
progress
|
NSProgress
|
An NSProgress
object containing the progress of the download. |
error
|
NSError
|
An error that occurred during download, if any. |
metadata
|
FIRStorageMetadata
|
nil
on downloads. |
task
|
FIRStorageDownloadTask
|
The task this is a snapshot of, which can be used to manage
( pause
, resume
, cancel
) the task. |
reference
|
FIRStorageReference
|
The reference this task came from. |
You can also remove observers, either individually, by status, or by removing all of them.
Swift
// Create a task listener handle let observer = downloadTask . observe (. progress ) { snapshot in // A progress event occurred } // Remove an individual observer downloadTask . removeObserver ( withHandle : observer ) // Remove all observers of a particular status downloadTask . removeAllObservers ( for : . progress ) // Remove all observers downloadTask . removeAllObservers ()
Objective-C
// Create a task listener handle NSString * observer = [ downloadTask observeStatus : FIRStorageTaskStatusProgress handler : ^ ( FIRStorageTaskSnapshot * snapshot ) { // A progress event occurred }]; // Remove an individual observer [ downloadTask removeObserverWithHandle : observer ]; // Remove all observers of a particular status [ downloadTask removeAllObserversForStatus : FIRStorageTaskStatusProgress ]; // Remove all observers [ downloadTask removeAllObservers ];
To prevent memory leaks, all observers are removed after an FIRStorageTaskStatusSuccess
or FIRStorageTaskStatusFailure
occurs.
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 downloading to a local file with error handling is shown below:
Swift
// Create a reference to the file we want to download let starsRef = storageRef . child ( "images/stars.jpg" ) // Start the download (in this case writing to a file) let downloadTask = storageRef . write ( toFile : localURL ) // Observe changes in status downloadTask . observe (. resume ) { snapshot in // Download resumed, also fires when the download starts } downloadTask . observe (. pause ) { snapshot in // Download paused } downloadTask . observe (. progress ) { snapshot in // Download reported progress let percentComplete = 100.0 * Double ( snapshot . progress !. completedUnitCount ) / Double ( snapshot . progress !. totalUnitCount ) } downloadTask . observe (. success ) { snapshot in // Download completed successfully } // Errors only occur in the "Failure" case downloadTask . observe (. failure ) { snapshot in guard let errorCode = ( snapshot . error as ? NSError )?. code else { return } guard let error = StorageErrorCode ( rawValue : errorCode ) else { return } switch ( error ) { case . objectNotFound : // File doesn't exist break case . unauthorized : // User doesn't have permission to access file break case . cancelled : // User cancelled the download break /* ... */ case . unknown : // Unknown error occurred, inspect the server response break default : // Another error occurred. This is a good place to retry the download. break } }
Objective-C
// Create a reference to the file we want to download FIRStorageReference * starsRef = [ storageRef child : @"images/stars.jpg" ]; // Start the download (in this case writing to a file) FIRStorageDownloadTask * downloadTask = [ storageRef writeToFile : localURL ]; // Observe changes in status [ downloadTask observeStatus : FIRStorageTaskStatusResume handler :^ ( FIRStorageTaskSnapshot * snapshot ) { // Download resumed, also fires when the download starts }]; [ downloadTask observeStatus : FIRStorageTaskStatusPause handler :^ ( FIRStorageTaskSnapshot * snapshot ) { // Download paused }]; [ downloadTask observeStatus : FIRStorageTaskStatusProgress handler :^ ( FIRStorageTaskSnapshot * snapshot ) { // Download reported progress double percentComplete = 100.0 * ( snapshot . progress . completedUnitCount ) / ( snapshot . progress . totalUnitCount ); }]; [ downloadTask observeStatus : FIRStorageTaskStatusSuccess handler :^ ( FIRStorageTaskSnapshot * snapshot ) { // Download completed successfully }]; // Errors only occur in the "Failure" case [ downloadTask observeStatus : FIRStorageTaskStatusFailure handler :^ ( FIRStorageTaskSnapshot * snapshot ) { if ( snapshot . error != nil ) { switch ( snapshot . error . code ) { case FIRStorageErrorCodeObjectNotFound : // File doesn't exist break ; case FIRStorageErrorCodeUnauthorized : // User doesn't have permission to access file break ; case FIRStorageErrorCodeCancelled : // User canceled the upload break ; /* ... */ case FIRStorageErrorCodeUnknown : // Unknown error occurred, inspect the server response break ; } } }];
You can also get and update metadata for files that are stored in Cloud Storage .
