在 iOS 上创建存储引用

您的文件存储在 Google Cloud Storage 存储分区中。此存储分区中的文件以层次结构的形式呈现,就像本地硬盘中的文件系统或 Firebase 实时数据库中的数据一样。通过创建对文件的引用,您的应用可以获得对相应文件的访问权限。这些引用随后可用于上传或下载数据、获取或更新元数据,或者删除文件。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 实时数据库,应当很熟悉这些路径。只不过,您的文件数据存储在 Google Cloud Storage 中,而不是存储在实时数据库中。

创建引用

要上传、下载或删除文件,或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。由于引用属于轻型项目,因此您可以根据需要创建多个引用。 引用还可以在多个操作中复用。

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];
    

您可在现有引用上使用 child 方法,以创建对树中较低位置(例如 '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"];
     

您还可以使用 parentroot 方法在我们的文件层次结构中向上导航。parent 可向上导航一级,而 root 可直接导航到根目录。

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];
    

childparentroot 可以多次链接到一起,每次都会返回一个引用。rootparent 例外,它会返回 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 fullPathnamebucket 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:

  1. 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。
  2. 不得包含回车符或换行符。
  3. 避免使用 #[]*?,因为这些字符在 Firebase 实时数据库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,我们将了解如何向 Cloud Storage 上传文件

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