在 Apple 平台上创建 Cloud Storage 引用

您的文件存储在 Cloud Storage 存储桶中。此存储桶中的文件以分层结构存储，就像本地硬盘中的文件系统或 Firebase Realtime Database 中的数据一样。通过创建指向文件的引用，您的应用便可以访问相应文件。然后，借助所创建的这些引用，您可以上传或下载数据、获取或更新元数据，也可以删除文件。引用可以指向特定的文件，也可以指向层次结构中更高层级的节点。

如果您使用过 Firebase Realtime Database，应当非常熟悉这些路径。只不过，您的文件数据存储在 Cloud Storage 中，而不是存储在 Realtime Database 中。

创建引用

如需上传、下载或删除文件，或者需要获取或更新文件的元数据，请创建引用。引用可以看作是指向云端文件的指针。由于引用属于轻型对象，因此您可以根据需要创建任意多个引用。这些引用可以重复用于多个操作。

引用是使用 FirebaseStorage 服务并调用其 reference 方法创建的。

Swift

// Get a reference to the storage service using the default Firebase App
let storage = Storage.storage()

// Create a storage reference from our storage service
let storageRef = storage.reference()

Objective-C

// Get a reference to the storage service using the default Firebase App
FIRStorage *storage = [FIRStorage storage];

// Create a storage reference from our storage service
FIRStorageReference *storageRef = [storage reference];

您可以对现有引用使用 child 方法，创建对树中层级较低位置（如 'images/space.jpg'）的引用。

Swift

// Create a child reference
// imagesRef now points to "images"
let imagesRef = storageRef.child("images")

// Child references can also take paths delimited by '/'
// spaceRef now points to "images/space.jpg"
// imagesRef still points to "images"
var spaceRef = storageRef.child("images/space.jpg")

// This is equivalent to creating the full reference
let storagePath = "\(your_firebase_storage_bucket)/images/space.jpg"
spaceRef = storage.reference(forURL: storagePath)

Objective-C

// Create a child reference
// imagesRef now points to "images"
FIRStorageReference *imagesRef = [storageRef child:@"images"];

// Child references can also take paths delimited by '/'
// spaceRef now points to "images/space.jpg"
// imagesRef still points to "images"
FIRStorageReference *spaceRef = [storageRef child:@"images/space.jpg"];

// This is equivalent to creating the full reference
spaceRef = [storage referenceForURL:@"gs://<your-firebase-storage-bucket>/images/space.jpg"];

通过引用进行导航

您还可以使用 parent 和 root 方法，在我们的文件层次结构中向上导航。parent 可以向上导航一级，而 root 可以一直导航至根目录。

Swift

// Parent allows us to move to the parent of a reference
// imagesRef now points to 'images'
let imagesRef = spaceRef.parent()

// Root allows us to move all the way back to the top of our bucket
// rootRef now points to the root
let rootRef = spaceRef.root()

Objective-C

// Parent allows us to move to the parent of a reference
// imagesRef now points to 'images'
imagesRef = [spaceRef parent];

// Root allows us to move all the way back to the top of our bucket
// rootRef now points to the root
FIRStorageReference *rootRef = [spaceRef root];

child、parent 和 root 可以链接在一起并链接多次，每次都会返回一个引用。root 的 parent 例外，它是 nil。

Swift

// References can be chained together multiple times
// earthRef points to "images/earth.jpg"
let earthRef = spaceRef.parent()?.child("earth.jpg")

// nilRef is nil, since the parent of root is nil
let nilRef = spaceRef.root().parent()

Objective-C

// References can be chained together multiple times
// earthRef points to "images/earth.jpg"
FIRStorageReference *earthRef = [[spaceRef parent] child:@"earth.jpg"];

// nilRef is nil, since the parent of root is nil
FIRStorageReference *nilRef = [[spaceRef root] parent];

引用的属性

您可以检查引用的 fullPath、name 和 bucket 属性，以便更好地了解它们指向的文件。这些属性会反映出文件的完整路径、名称和存储分区。

Swift

// Reference's path is: "images/space.jpg"
// This is analogous to a file path on disk
spaceRef.fullPath

// Reference's name is the last segment of the full path: "space.jpg"
// This is analogous to the file name
spaceRef.name

// Reference's bucket is the name of the storage bucket where files are stored
spaceRef.bucket

Objective-C

// Reference's path is: "images/space.jpg"
// This is analogous to a file path on disk
spaceRef.fullPath;

// Reference's name is the last segment of the full path: "space.jpg"
// This is analogous to the file name
spaceRef.name;

// Reference's bucket is the name of the storage bucket where files are stored
spaceRef.bucket;

引用的限制

引用路径和名称可以包含有效 Unicode 字符的任意序列，但也必须遵循一些限制，具体包括：

使用 UTF-8 编码时，reference.fullPath 的总长度必须介于 1 到 1024 个字节之间。
不得包含回车符或换行符。
避免使用 #、[、]、* 或 ?，因为这些字符在 Firebase Realtime Database 或 gsutil 等其他工具中无法正常显示。

完整示例

Swift

// Points to the root reference
let storageRef = Storage.storage().reference()

// Points to "images"
let imagesRef = storageRef.child("images")

// Points to "images/space.jpg"
// Note that you can use variables to create child values
let fileName = "space.jpg"
let spaceRef = imagesRef.child(fileName)

// File path is "images/space.jpg"
let path = spaceRef.fullPath

// File name is "space.jpg"
let name = spaceRef.name

// Points to "images"
let images = spaceRef.parent()

Objective-C

// Points to the root reference
FIRStorageReference *storageRef = [[FIRStorage storage] reference];

// Points to "images"
FIRStorageReference *imagesRef = [storageRef child:@"images"];

// Points to "images/space.jpg"
// Note that you can use variables to create child values
NSString *fileName = @"space.jpg";
FIRStorageReference *spaceRef = [imagesRef child:fileName];

// File path is "images/space.jpg"
NSString *path = spaceRef.fullPath;

// File name is "space.jpg"
NSString *name = spaceRef.name;

// Points to "images"
imagesRef = [spaceRef parent];

接下来，我们将了解如何将文件上传到 Cloud Storage。