After uploading a file to Cloud Storage reference, you can also get
and update the file metadata, for example to update the content type. Files
can also store custom key/value pairs with additional file metadata.
File metadata contains common properties such as
Name
,
SizeBytes
, and
ContentType
(often referred to as MIME type) in addition to some
less common ones like
ContentDisposition
and
CreationTimeMillis
. This
metadata can be retrieved from a Cloud Storage reference using the
GetMetadataAsync
method.
// Create reference to the file whose metadata we want to retrieve
StorageReference forestRef =
storageRef.Child("images/forest.jpg");
// Get metadata properties
forestRef.GetMetadataAsync().ContinueWithOnMainThread(task => {
if (!task.IsFaulted && !task.IsCanceled) {
StorageMetadata meta = task.Result;
// do stuff with meta
}
});
You can update file metadata at any time after the file upload completes by
using the
UpdateMetadataAsync
method which takes a
MetadataChange
object.
Refer to the
full list
for more information on what
properties can be updated. Only the properties specified in the metadata are
updated, all others are left unmodified.
// Create reference to the file whose metadata we want to change
StorageReference forestRef = storageRef.Child("images/forest.jpg");
// Create file metadata to update
var newMetadata = new MetadataChange();
newMetadata.CacheControl = "public,max-age=300";
newMetadata.ContentType = "image/jpeg";
// Update metadata properties
forestRef.UpdateMetadataAsync(newMetadata).ContinueWithOnMainThread(task => {
if (!task.IsFaulted && !task.IsCanceled) {
// access the updated meta data
StorageMetadata meta = task.Result;
}
});
You can delete writable metadata properties by passing the empty string:
// Create file metadata to update
var newMetadata = new MetadataChange();
newMetadata.ContentType = "";
// Update metadata properties
forestRef.UpdateMetadataAsync(newMetadata).ContinueWithOnMainThread(task => {
if (!task.IsFaulted && !task.IsCanceled) {
StorageMetadata meta = task.Result;
// meta.ContentType should be an empty string now
}
});
Handle Errors
There are a number of reasons why errors may occur on getting or updating
metadata, 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.
You can specify custom metadata as a
Dictionary<string, string>
.
var newMetadata = new MetadataChange {
CustomMetadata = new Dictionary<string, string> {
{"location", "Yosemite, CA, USA"},
{"activity", "Hiking"}
}
};
// UpdateMetadataAsync
You can store app-specific data for each file in custom metadata, but we highly
recommend using a database (such as the
Firebase Realtime Database
) to store and synchronize this type of
data.
A full list of metadata properties on a file is available below:
Property
|
Type
|
Modifyable in MetadataChange
|
Bucket
|
string
|
NO
|
Generation
|
string
|
NO
|
MetadataGeneration
|
string
|
NO
|
Path
|
string
|
NO
|
Name
|
string
|
NO
|
SizeBytes
|
long
|
NO
|
CreationTimeMillis
|
long
|
NO
|
UpdatedTimeMillis
|
long
|
NO
|
CacheControl
|
string
|
YES
|
ContentDisposition
|
string
|
YES
|
ContentEncoding
|
string
|
YES
|
ContentLanguage
|
string
|
YES
|
ContentType
|
string
|
YES
|
DownloadUrl
|
Uri
|
NO
|
DownloadUrls
|
IList<Uri>
|
NO
|
CustomMetadataKeys
|
IEnumerable<string>
|
YES
|
Next Steps
Uploading, downloading, and updating files is important, but so is being able
to remove them. Let's learn how to
delete files
from Cloud Storage.