在 Apple 平台上建立 Cloud Storage 參考資料

您的檔案會儲存在 Cloud Storage 值區中。這個值區中的檔案會以階層式結構呈現，如同本機硬碟中的檔案系統，或是 Firebase 即時資料庫中的資料。建立檔案的參照後，應用程式就能取得該檔案的存取權。這些參照便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，或是階層中更高層級的節點。

如果您已使用過 Firebase 即時資料庫，應該不太熟悉這些路徑。不過，檔案資料儲存在 Cloud Storage 中，而「不是」儲存在即時資料庫中。

可建立參照

建立參照以上傳、下載或刪除檔案，或是取得或更新其中繼資料。參照可以視為雲端中檔案的指標，參照簡單，因此您可以視需要建立任意數量的參照。這些作業也能重複用於多項作業。

參照是使用 FirebaseStorage 服務建立，並呼叫其 reference 方法。

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];

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

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"];

您也可以使用 parent 和 root 方法向上瀏覽檔案階層。parent 會向上瀏覽一個層級，而 root 則會導覽至頂部。

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 可以多次鏈結，因為各自會傳回參照。例外狀況是 root 的 parent，也就是 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];

參照屬性

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

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;

參考檔案的限制

參照路徑和名稱可包含任何序列的有效 Unicode 字元，但系統會設下某些限制：

  1. 使用 UTF-8 編碼時，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. 避免使用 #、[、]、* 或 ?，因為這些工具並不適合與 Firebase 即時資料庫或 gsutil 等其他工具搭配使用。

完整範例

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];

接下來，我們將說明如何上傳檔案至 Cloud Storage。