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本頁面由 Cloud Translation API 翻譯而成。

在 Android 裝置上透過 Cloud Storage 下載檔案

Cloud Storage for Firebase 可讓您快速輕鬆地從 Firebase 提供及管理的 Cloud Storage 儲存體下載檔案。

可建立參照

如要下載檔案，請先為要下載的檔案建立 Cloud Storage 參照。

您可以將子路徑附加至 Cloud Storage 值區的根目錄，藉此建立參照，也可以從現有的 gs:// 或 https:// 網址建立參照，以便參照 Cloud Storage 中的物件。

Kotlin+KTX

// Create a storage reference from our app
val storageRef = storage.reference

// Create a reference with an initial file path and name
val pathReference = storageRef.child("images/stars.jpg")

// Create a reference to a file from a Google Cloud Storage URI
val gsReference = storage.getReferenceFromUrl("gs://bucket/images/stars.jpg")

// Create a reference from an HTTPS URL
// Note that in the URL, characters are URL escaped!
val httpsReference = storage.getReferenceFromUrl(
    "https://firebasestorage.googleapis.com/b/bucket/o/images%20stars.jpg",
)StorageActivity.kt

Java

// Create a storage reference from our app
StorageReference storageRef = storage.getReference();

// Create a reference with an initial file path and name
StorageReference pathReference = storageRef.child("images/stars.jpg");

// Create a reference to a file from a Google Cloud Storage URI
StorageReference gsReference = storage.getReferenceFromUrl("gs://bucket/images/stars.jpg");

// Create a reference from an HTTPS URL
// Note that in the URL, characters are URL escaped!
StorageReference httpsReference = storage.getReferenceFromUrl("https://firebasestorage.googleapis.com/b/bucket/o/images%20stars.jpg");StorageActivity.java

下載檔案

取得參照後，您可以呼叫 getBytes() 或 getStream()，從 Cloud Storage 下載檔案。如果您想使用其他程式庫下載檔案，可以使用 getDownloadUrl() 取得下載網址。

在記憶體中下載

使用 getBytes() 方法將檔案下載至 byte[]。這是下載檔案最簡單的方式，但必須將整個檔案內容載入記憶體。如果您要求的檔案大小超過應用程式可用的記憶體，應用程式就會當機。為避免記憶體問題，getBytes() 會下載最多位元組。請將大小上限設為應用程式可處理的項目，或使用其他下載方法。

Kotlin+KTX

var islandRef = storageRef.child("images/island.jpg")

val ONE_MEGABYTE: Long = 1024 * 1024
islandRef.getBytes(ONE_MEGABYTE).addOnSuccessListener {
    // Data for "images/island.jpg" is returned, use this as needed
}.addOnFailureListener {
    // Handle any errors
}StorageActivity.kt

Java

StorageReference islandRef = storageRef.child("images/island.jpg");

final long ONE_MEGABYTE = 1024 * 1024;
islandRef.getBytes(ONE_MEGABYTE).addOnSuccessListener(new OnSuccessListener<byte[]>() {
    @Override
    public void onSuccess(byte[] bytes) {
        // Data for "images/island.jpg" is returns, use this as needed
    }
}).addOnFailureListener(new OnFailureListener() {
    @Override
    public void onFailure(@NonNull Exception exception) {
        // Handle any errors
    }
});StorageActivity.java

下載至本機檔案

getFile() 方法會將檔案直接下載到本機裝置。如果使用者想要在離線時存取檔案，或是在其他應用程式中共用檔案，請使用這個選項。getFile() 會傳回 DownloadTask，讓您用來管理下載內容及監控下載狀態。

Kotlin+KTX

islandRef = storageRef.child("images/island.jpg")

val localFile = File.createTempFile("images", "jpg")

islandRef.getFile(localFile).addOnSuccessListener {
    // Local temp file has been created
}.addOnFailureListener {
    // Handle any errors
}StorageActivity.kt

Java

islandRef = storageRef.child("images/island.jpg");

File localFile = File.createTempFile("images", "jpg");

islandRef.getFile(localFile).addOnSuccessListener(new OnSuccessListener<FileDownloadTask.TaskSnapshot>() {
    @Override
    public void onSuccess(FileDownloadTask.TaskSnapshot taskSnapshot) {
        // Local temp file has been created
    }
}).addOnFailureListener(new OnFailureListener() {
    @Override
    public void onFailure(@NonNull Exception exception) {
        // Handle any errors
    }
});StorageActivity.java

如要主動管理下載內容，請參閱「管理下載內容」一文瞭解詳情。

透過網址下載資料

如果您已經有以網址為基礎的下載基礎架構，或是只想取得要分享的網址，您可以在 Cloud Storage 參照上呼叫 getDownloadUrl() 方法，取得檔案的下載網址。

Kotlin+KTX

storageRef.child("users/me/profile.png").downloadUrl.addOnSuccessListener {
    // Got the download URL for 'users/me/profile.png'
}.addOnFailureListener {
    // Handle any errors
}StorageActivity.kt

Java

storageRef.child("users/me/profile.png").getDownloadUrl().addOnSuccessListener(new OnSuccessListener<Uri>() {
    @Override
    public void onSuccess(Uri uri) {
        // Got the download URL for 'users/me/profile.png'
    }
}).addOnFailureListener(new OnFailureListener() {
    @Override
    public void onFailure(@NonNull Exception exception) {
        // Handle any errors
    }
});StorageActivity.java

使用 FirebaseUI 下載圖片

FirebaseUI 提供簡單、可自訂且可用於實際工作環境的原生行動裝置繫結，可消除樣板程式碼並推廣 Google 最佳做法。使用 FirebaseUI，您可以透過與 Glide 整合的功能，快速輕鬆地從 Cloud Storage 下載、快取及顯示圖片。

首先，請將 FirebaseUI 新增至 app/build.gradle：

dependencies {
    // FirebaseUI Storage only
    implementation 'com.firebaseui:firebase-ui-storage:7.2.0'
}

接著，您可以直接從 Cloud Storage 將圖片載入 ImageView：

Kotlin+KTX

// Reference to an image file in Cloud Storage
val storageReference = Firebase.storage.reference

// ImageView in your Activity
val imageView = findViewById<ImageView>(R.id.imageView)

// Download directly from StorageReference using Glide
// (See MyAppGlideModule for Loader registration)
Glide.with(context)
    .load(storageReference)
    .into(imageView)FirebaseUIActivity.kt

Java

// Reference to an image file in Cloud Storage
StorageReference storageReference = FirebaseStorage.getInstance().getReference();

// ImageView in your Activity
ImageView imageView = findViewById(R.id.imageView);

// Download directly from StorageReference using Glide
// (See MyAppGlideModule for Loader registration)
Glide.with(context)
        .load(storageReference)
        .into(imageView);FirebaseUIActivity.java

處理活動生命週期變更

即使活動生命週期變更 (例如顯示對話方塊或旋轉螢幕)，下載作業仍會在背景繼續進行。您附加的任何事件監聽器也會保留附加狀態。如果在活動停止後呼叫，可能會產生非預期的結果。

您可以透過活動範圍訂閱事件監聽器，解決這個問題，這樣一來，活動停止時就會自動取消註冊。接著，在活動重新啟動時使用 getActiveDownloadTasks 方法，取得仍在執行或最近完成的下載作業。

下例示範了這個做法，並示範如何保存所使用的儲存空間參照路徑。

Kotlin+KTX

override fun onSaveInstanceState(outState: Bundle) {
    super.onSaveInstanceState(outState)

    // If there's a download in progress, save the reference so you can query it later
    outState.putString("reference", storageRef.toString())
}

override fun onRestoreInstanceState(savedInstanceState: Bundle) {
    super.onRestoreInstanceState(savedInstanceState)

    // If there was a download in progress, get its reference and create a new StorageReference
    val stringRef = savedInstanceState.getString("reference") ?: return

    storageRef = Firebase.storage.getReferenceFromUrl(stringRef)

    // Find all DownloadTasks under this StorageReference (in this example, there should be one)
    val tasks = storageRef.activeDownloadTasks

    if (tasks.size > 0) {
        // Get the task monitoring the download
        val task = tasks[0]

        // Add new listeners to the task using an Activity scope
        task.addOnSuccessListener(this) {
            // Success!
            // ...
        }
    }
}DownloadActivity.kt

Java

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);

    // If there's a download in progress, save the reference so you can query it later
    if (mStorageRef != null) {
        outState.putString("reference", mStorageRef.toString());
    }
}

@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
    super.onRestoreInstanceState(savedInstanceState);

    // If there was a download in progress, get its reference and create a new StorageReference
    final String stringRef = savedInstanceState.getString("reference");
    if (stringRef == null) {
        return;
    }
    mStorageRef = FirebaseStorage.getInstance().getReferenceFromUrl(stringRef);

    // Find all DownloadTasks under this StorageReference (in this example, there should be one)
    List<FileDownloadTask> tasks = mStorageRef.getActiveDownloadTasks();
    if (tasks.size() > 0) {
        // Get the task monitoring the download
        FileDownloadTask task = tasks.get(0);

        // Add new listeners to the task using an Activity scope
        task.addOnSuccessListener(this, new OnSuccessListener<FileDownloadTask.TaskSnapshot>() {
            @Override
            public void onSuccess(FileDownloadTask.TaskSnapshot state) {
                // Success!
                // ...
            }
        });
    }
}DownloadActivity.java

處理錯誤

下載時可能會發生錯誤，原因有很多，包括檔案不存在，或使用者沒有權限存取所需檔案。如要進一步瞭解錯誤，請參閱說明文件的「處理錯誤」一節。

完整範例

以下是下載作業的完整範例，其中包含錯誤處理：

Kotlin+KTX

storageRef.child("users/me/profile.png").getBytes(Long.MAX_VALUE).addOnSuccessListener {
    // Use the bytes to display the image
}.addOnFailureListener {
    // Handle any errors
}StorageActivity.kt

Java

storageRef.child("users/me/profile.png").getBytes(Long.MAX_VALUE).addOnSuccessListener(new OnSuccessListener<byte[]>() {
    @Override
    public void onSuccess(byte[] bytes) {
        // Use the bytes to display the image
    }
}).addOnFailureListener(new OnFailureListener() {
    @Override
    public void onFailure(@NonNull Exception exception) {
        // Handle any errors
    }
});StorageActivity.java

您也可以為儲存在 Cloud Storage 中的檔案取得與更新中繼資料。