使用DownloadManager.setDestinationInExternalPublicDir创建自定义目录存储Firebase下载文件报错问题咨询

I've run into this exact issue before—here's what's going on and how to fix it:

The error pops up because DownloadManager.Request.setDestinationInExternalPublicDir() requires its first parameter to be one of Android's official standard directory constants (like Environment.DIRECTORY_DOWNLOADS or Environment.DIRECTORY_PICTURES). You can't pass a raw custom path like "/folder/innerFolder" directly here.

To save files to a custom folder, you need to manually create the folder first, then use setDestinationUri() to point the DownloadManager to your custom path. Here's the step-by-step solution:

1. Create Your Custom Folder #

We'll make a subfolder inside a standard public directory (like Downloads) to stay compliant with Android's storage rules. For example, let's create a folder called FirebaseMedia/EventAssets inside the system Downloads directory:

// Define the custom folder path
File customStorageDir = new File(
    Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS),
    "FirebaseMedia/EventAssets"
);

// Create the folder if it doesn't exist (creates parent folders automatically)
if (!customStorageDir.exists()) {
    boolean folderCreated = customStorageDir.mkdirs();
    if (!folderCreated) {
        Toast.makeText(SearchCase.this, "לא ניתן ליצור תי�рани אחסון", Toast.LENGTH_SHORT).show();
        return;
    }
}

2. Update the DownloadManager Request #

Replace the problematic setDestinationInExternalPublicDir() call with setDestinationUri(), which lets you specify a full custom file path:

// Build the full path for the downloaded file
File destinationFile = new File(customStorageDir, title);
Uri destinationUri = Uri.fromFile(destinationFile);

// Set the custom storage destination
request.setDestinationUri(destinationUri);

3. Handle Permissions (Critical!) #

• Android 9 (API 28) and below: Declare the WRITE_EXTERNAL_STORAGE permission in your AndroidManifest.xml and request it at runtime from the user.
• Android 10 (API 29) and above:
  • Option 1: Add android:requestLegacyExternalStorage="true" to your <application> tag in AndroidManifest.xml (works for API 29 only)
  • Option 2: Request the MANAGE_EXTERNAL_STORAGE permission (only use this if your app truly needs broad, unrestricted storage access)

Full Modified Code Snippet #

Here's how your updated onDataChange method will look:

@Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
    mStoredPictures = new ArrayList<>();
    if (snapshot.exists()) {
        // Step 1: Create custom storage folder
        File customStorageDir = new File(
            Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS),
            "FirebaseMedia/EventAssets"
        );
        if (!customStorageDir.exists()) {
            boolean folderCreated = customStorageDir.mkdirs();
            if (!folderCreated) {
                Toast.makeText(SearchCase.this, "לא ניתן ליצור תי�рани אחסון", Toast.LENGTH_SHORT).show();
                return;
            }
        }

        for (DataSnapshot postSnapShot : snapshot.getChildren()) {
            StoredPicture storedPicture = postSnapShot.getValue(StoredPicture.class);
            mStoredPictures.add(storedPicture);
            String imageUrl = storedPicture.getmImageUrl();
            
            DownloadManager.Request request = new DownloadManager.Request(Uri.parse(imageUrl));
            String title = URLUtil.guessFileName(imageUrl, null, null);
            request.setTitle(nameGet1 + "-" + idGet1);
            request.setDescription("----");
            
            String cookie = CookieManager.getInstance().getCookie(imageUrl);
            request.addRequestHeader("cookie", cookie);
            request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
            
            // Step 2: Set custom destination path
            File destinationFile = new File(customStorageDir, title);
            Uri destinationUri = Uri.fromFile(destinationFile);
            request.setDestinationUri(destinationUri);
            
            DownloadManager downloadManager = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
            downloadManager.enqueue(request);
            Toast.makeText(SearchCase.this, "מוריד תמונות/סרטונים...", Toast.LENGTH_SHORT).show();
        }
    }
}

After this change, your files will be saved to Internal Storage/Download/FirebaseMedia/EventAssets instead of the default Downloads folder, and you won't see that error anymore.

内容的提问来源于stack exchange，提问作者Maklonim