在 Apple 平台上建立 Cloud Storage 參考資料

檔案會儲存在 Cloud Storage 值區中。這個值區中的檔案會以階層結構呈現，就像本機硬碟上的檔案系統，或 Firebase Realtime Database 中的資料一樣。建立檔案參照後，應用程式就能取得檔案存取權。這些參照可用於上傳或下載資料、取得或更新中繼資料，或刪除檔案。參照可以指向特定檔案，也可以指向階層中較高層級的節點。

如果您曾使用 Firebase Realtime Database，這些路徑應該會讓您感到很熟悉。不過，您的檔案資料會儲存在 Cloud Storage 中，而非 儲存在 Realtime Database 中。

可建立參照

建立參照，以便上傳、下載或刪除檔案，或取得/更新檔案中繼資料。您可以將參照視為指向雲端檔案的指標。參照項目的大小輕巧，因此您可以視需要建立多個參照項目。這些函式也可用於多項作業。

您可以使用 FirebaseStorage 服務並呼叫其 reference 方法來建立參照。

SwiftObjective-C 
// 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()
    
// 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];

您可以使用現有參照的 child 方法，建立樹狀結構中較低位置的參照，例如 'images/space.jpg'。

SwiftObjective-C 
// 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)
    
// 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"];

您也可以使用 parent 和 root 方法，在檔案階層中向上瀏覽。parent 會向上瀏覽一層，而 root 會一直瀏覽至頂端。

SwiftObjective-C 
// 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()
    
// 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 可以連結多次，因為每個都會傳回參照。例外狀況是 root 的 parent，即 nil。

SwiftObjective-C 
// 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()
    
// 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];

參照屬性

您可以使用 fullPath、name 和 bucket 屬性檢查參照，進一步瞭解參照所指向的檔案。這些屬性會取得檔案的完整路徑、名稱和值區。

SwiftObjective-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
    
// 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;

參照資料限制

參照路徑和名稱可包含任何有效的 Unicode 字元序列，但有以下限制：

  1. 如果使用 UTF-8 編碼，reference.fullPath 的總長度必須介於 1 到 1024 個位元組之間。
  2. 不得使用回車或換行字元。
  3. 請避免使用 #、[、]、* 或 ?，因為這些工具無法與 Firebase Realtime Database 或 gsutil 等其他工具搭配使用。

完整範例

SwiftObjective-C 
// 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()
    
// 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];

接下來，我們將說明如何上傳檔案至 Cloud Storage。