Download files from Cloud Storage

In our last section, we learned the different ways of uploading files. Now, we will learn how to download the files from the Cloud Storage. For downloading a file, first, we have to create a Cloud Storage reference to the file which we want to download.

There are following two ways through which we can create a reference, i.e., by appending child paths to the storage root and from an existing gs:// or https://URL referencing an object in the Cloud Storage.

// Creating a storage reference from our app
val storageRef = storage.reference

// Creating a reference with an initial file path and name
val pathReference = storageRef.child("images/stars.jpg")

// Creating a reference to a file from a Google Cloud Storage URI
val gsReference = storage.getReferenceFromUrl("gs://bucket/images/stars.jpg")

// Creating a reference from an HTTPS URL
// In the URL, characters are URL escaped!
val httpsReference = storage.getReferenceFromUrl(
        "https://firebasestorage.googleapis.com/b/bucket/o/images%20stars.jpg")

Downloading Methods

After creating an appropriate reference, we call various methods to download files, i.e., getBytes(), getStream(), or we can get a download URL with getDownloadUrl() for downloading the file with another library.

The use of the getBytes() method is the easiest way of downloading the file to memory. If we request a file larger than our app's available memory, our app will crash. The getBytes() takes a maximum amount of bytes to download. We set the maximum size according to our app capability.

var jtpRef = storageRef.child("images/jtp.jpg")

val ONE_MEGABYTE: Long = 1024 * 1024
islandRef.getBytes(ONE_MEGABYTE).addOnSuccessListener {
    // Data for "images/jtp.jpg" is returned, use this as needed
}.addOnFailureListener {
    // Handling any errors
}

Downloading Data to a Local File

If we want to have access to the file while offline or to share the file, then we use the getFile() method. This method downloads a file directly to a local device. This method returns a DownloadTask, which we can use to manage our downloads and monitor the status.

jtpRef = storageRef.child("images/jtp.jpg")

val localFile = File.createTempFile("images", "jpg")

jtpRef.getFile(localFile).addOnSuccessListener {
    // Local temp file has been created
}.addOnFailureListener {
    // Handling any errors
}

Downloading Data via URL

If we already have the download infrastructure based on the URL, or simply want to share a URL, we can get the download URL for the file by calling the getDownloadUrl () method on the storage context.

storageRef.child("users/me/profile.png").downloadUrl.addOnSuccessListener {
    // Getting the download URL for 'users/me/profile.png'
}.addOnFailureListener {
    // Handling any errors
}

Downloading images with FirebaseUI

For eliminating boilerplate code and promoting Google best practices. FirebaseUI provides simple, customized, and production-ready native mobile bindings. Using FirebaseUI, we can quickly, easily download, cache, and display images from cloud storage using our integration with Glide.

First, add FirebaseUI to our app/build.gradle:

dependencies {
    // FirebaseUI Storage only
    implementation 'com.firebaseui:firebase-ui-storage:4.3.1'
}

Then we can load images directly from storage into an ImageView:

// Referencing to an image file in Cloud Storage
val storageReference = FirebaseStorage.getInstance().reference

// ImageView in our Activity
val imageView = findViewById<ImageView>(R.id.imageView)

// Downloading directly from StorageReference using Glide
Glide.with(this /* context */)
        .load(storageReference)
        .into(imageView)

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