Upload files with Cloud Storage on Flutter

Cloud Storage for Firebase allows you to quickly and easily upload files to a Cloud Storage bucket provided and managed by Firebase.

Upload Files

To upload a file to Cloud Storage, you first create a reference to the full path of the file, including the file name.

// Create a storage reference from our app
final storageRef = FirebaseStorage.instance.ref();

// Create a reference to "mountains.jpg"
final mountainsRef = storageRef.child("mountains.jpg");

// Create a reference to 'images/mountains.jpg'
final mountainImagesRef = storageRef.child("images/mountains.jpg");

// While the file names are the same, the references point to different files
assert(mountainsRef.name == mountainImagesRef.name);
assert(mountainsRef.fullPath != mountainImagesRef.fullPath);

Once you've created an appropriate reference, you then call the putFile(), putString(), or putData() method to upload the file to Cloud Storage.

You cannot upload data with a reference to the root of your Cloud Storage bucket. Your reference must point to a child URL.

Upload from a file

To upload a file, you must first get the absolute path to its on-device location. For example, if a file exists within the application's documents directory, use the official path_provider package to generate a file path and pass it to putFile():

Directory appDocDir = await getApplicationDocumentsDirectory();
String filePath = '${appDocDir.absolute}/file-to-upload.png';
File file = File(filePath);

try {
  await mountainsRef.putFile(file);
} on firebase_core.FirebaseException catch (e) {
  // ...
}

Upload from a String

You can upload data as a raw, base64, base64url, or data_url encoded string using the putString() method. For example, to upload a text string encoded as a Data URL:

String dataUrl = 'data:text/plain;base64,SGVsbG8sIFdvcmxkIQ==';

try {
  await mountainsRef.putString(dataUrl, format: PutStringFormat.dataUrl);
} on FirebaseException catch (e) {
  // ...
}

Uploading raw data

You can upload lower-level typed data in the form of a Uint8List for those cases where uploading a string or File is not practical. In this case, call the putData() method with your data:

try {
  // Upload raw data.
  await mountainsRef.putData(data);
} on firebase_core.FirebaseException catch (e) {
  // ...
}

Get a download URL

After uploading a file, you can get a URL to download the file by calling the getDownloadUrl() method on the Reference:

await mountainsRef.getDownloadURL();

Add File Metadata

You can also include metadata when you upload files. This metadata contains typical file metadata properties such as contentType (commonly referred to as MIME type). The putFile() method automatically infers the MIME type from the File extension, but you can override the auto-detected type by specifying contentType in the metadata. If you do not provide a contentType and Cloud Storage cannot infer a default from the file extension, Cloud Storage uses application/octet-stream. See Use File Metadata.

try {
  await mountainsRef.putFile(file, SettableMetadata(
    contentType: "image/jpeg",
  ));
} on firebase_core.FirebaseException catch (e) {
  // ...
}

Manage Uploads

In addition to starting uploads, you can pause, resume, and cancel uploads using the pause(), resume(), and cancel() methods. Pause and resume events raise pause and progress state changes respectively. Canceling an upload causes the upload to fail with an error indicating that the upload was canceled.

final task = mountainsRef.putFile(largeFile);

// Pause the upload.
bool paused = await task.pause();
print('paused, $paused');

// Resume the upload.
bool resumed = await task.resume();
print('resumed, $resumed');

// Cancel the upload.
bool canceled = await task.cancel();
print('canceled, $canceled');

Monitor Upload Progress

You can listen to a task's event stream to handle success, failure, progress, or pauses in your upload task:

Event Type Typical Usage
TaskState.running Emitted periodically as data is transferred and can be used to populate an upload/download indicator.
TaskState.paused Emitted any time the task is paused.
TaskState.success Emitted when the task has successfully completed.
TaskState.canceled Emitted any time the task is canceled.
TaskState.error Emitted when the upload has failed. This can happen due to network timeouts, authorization failures, or if you cancel the task. 
mountainsRef.putFile(file).snapshotEvents.listen((taskSnapshot) {
  switch (taskSnapshot.state) {
    case TaskState.running:
      // ...
      break;
    case TaskState.paused:
      // ...
      break;
    case TaskState.success:
      // ...
      break;
    case TaskState.canceled:
      // ...
      break;
    case TaskState.error:
      // ...
      break;
  }
});

Error Handling

There are a number of reasons why errors may occur on upload, including the local file not existing, or the user not having permission to upload the desired file. You can find more information about errors in the Handle Errors section of the docs.

Full Example

A full example of an upload with progress monitoring and error handling is shown below:

final appDocDir = await getApplicationDocumentsDirectory();
final filePath = "${appDocDir.absolute}/path/to/mountains.jpg";
final file = File(filePath);

// Create the file metadata
final metadata = SettableMetadata(contentType: "image/jpeg");

// Create a reference to the Firebase Storage bucket
final storageRef = FirebaseStorage.instance.ref();

// Upload file and metadata to the path 'images/mountains.jpg'
final uploadTask = storageRef
    .child("images/path/to/mountains.jpg")
    .putFile(file, metadata);

// Listen for state changes, errors, and completion of the upload.
uploadTask.snapshotEvents.listen((TaskSnapshot taskSnapshot) {
  switch (taskSnapshot.state) {
    case TaskState.running:
      final progress =
          100.0 * (taskSnapshot.bytesTransferred / taskSnapshot.totalBytes);
      print("Upload is $progress% complete.");
      break;
    case TaskState.paused:
      print("Upload is paused.");
      break;
    case TaskState.canceled:
      print("Upload was canceled");
      break;
    case TaskState.error:
      // Handle unsuccessful uploads
      break;
    case TaskState.success:
      // Handle successful uploads on complete
      // ...
      break;
  }
});

Now that you've uploaded files, let's learn how to download them from Cloud Storage.