Android 11下使用Xamarin.Forms无法下载部分文件求助（附Manifest代码）

Hey there! As someone who’s helped plenty of new Xamarin.Forms devs work through Android 11 storage and download headaches, let’s break down the most common culprits here—since Android 11 (API 30) made big changes to how apps access storage, that’s almost certainly where your issue lies.

First, let’s cover the key Android 11 changes that affect file downloads, then walk through what to check in your AndroidManifest.xml.

Common Android 11 Pitfalls & Manifest Fixes #

1. Partitioned Storage is Enabled by Default #

Android 11 introduced partitioned storage, which restricts apps from accessing most of the external storage by default. If your download code is trying to save files to a traditional location like /sdcard/ or a custom folder outside your app’s private storage, it’ll fail silently or throw an error.

Quick Temporary Fix: If you haven’t had time to fully adapt to partitioned storage, add this attribute to your <application> tag in the manifest to opt into the legacy storage model (note: this won’t work on API 31+):

<application ... android:requestLegacyExternalStorage="true">

Long-Term Proper Fix: Update your download logic to use either:

• Your app’s private external storage: Use Context.GetExternalFilesDir(null) to get a directory that only your app can access (no extra permissions needed)
• Public media directories (like Downloads): Use MediaStore to save files here, which requires the READ_EXTERNAL_STORAGE permission (and WRITE_EXTERNAL_STORAGE for devices below API 30)

2. Missing or Incorrect Permissions #

Android 11 changed how storage permissions work, so your manifest might be missing critical declarations:

Make sure these permissions are present (adjust based on your download target):

<!-- Required for any network-based download -->
<uses-permission android:name="android.permission.INTERNET" />

<!-- Needed to read from public storage (if your app accesses downloaded files later) -->
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

<!-- Only needed for devices below API 30; has no effect on Android 11+ -->
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" android:maxSdkVersion="29" />

⚠️ Important Note: If you need full access to all external storage (e.g., a file manager app), you’ll need the MANAGE_EXTERNAL_STORAGE permission—but this is a restricted permission that requires users to enable it manually in settings, and Google may reject apps using it unnecessarily.

3. Overlooking Network Access #

It sounds obvious, but I’ve seen devs miss this all the time: if your download relies on the internet, you must have the INTERNET permission in your manifest. Without it, your app won’t be able to connect to the server to fetch the file at all.

Next Steps #

Could you share your full AndroidManifest.xml code? That’ll help me spot any other misconfigurations. But even without seeing it, start by checking the points above—most Android 11 download failures boil down to partitioned storage or permission issues.

内容的提问来源于stack exchange，提问作者gadda raju