Xamarin.Forms

Question

在我的应用程序中，我提供了下载 PDF 格式报告的功能。一切都很好，直到我在 Android 10 及以下版本上测试我的应用程序。最近我将设备更新为 Android 11，现在我无法下载共享存储中的任何文件。下载文件时出现 Access Denied 错误。

我已授予读取和写入外部存储的权限

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

我的下载路径是

Android.OS.Environment.GetExternalStoragePublicDirectory(Android.OS.Environment.DirectoryDownloads).AbsolutePath;

我在AndroidManifest.xml

中也设置了android:requestLegacyExternalStorage="true"

我下载文件的代码如下所示

public async void DownloadSupplierSample(object sender, EventArgs e)
    {
        try
        {
            string basepath;
            if (Device.RuntimePlatform == Device.Android)
                basepath = DependencyService.Get<IDownloadPath>().GetDownloadsPath();
            else
                basepath = System.IO.Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Personal), "..", "Library");

            PermissionStatus readstatus = await Permissions.CheckStatusAsync<Permissions.StorageRead>();
            PermissionStatus writestatus = await Permissions.CheckStatusAsync<Permissions.StorageWrite>();

            if (readstatus == PermissionStatus.Granted && writestatus == PermissionStatus.Granted)
            {
                DownloadSupplier(basepath);
            }
            else
            {
                var read = await Permissions.RequestAsync<Permissions.StorageRead>();
                var write = await Permissions.RequestAsync<Permissions.StorageWrite>();

                if (read == PermissionStatus.Granted && write == PermissionStatus.Granted)
                {
                    DownloadSupplier(basepath);
                }
            }
            await DisplayAlert("", "Sample is downaloaded at Downloads directory","Ok");
        }
        catch (Exception ex)
        {
        }
    }

    async void DownloadSupplier(string basepath)
    {
        using (var stream = await FileSystem.OpenAppPackageFileAsync("SupplierMaster.xlsx"))
        {
            string filename = $"SupplierMaster_{DateTime.Now.ToString("yyyyMMddHHmmss")}.xlsx";
            string filepath = Path.Combine(basepath, filename);

            byte[] bytes = Utils.Common.StreamToBytes(stream);
            File.WriteAllBytes(filepath, bytes);
            //using (Stream filestream = File.Create(filepath))
            //{
            //    //stream.Seek(0, SeekOrigin.Begin);
            //    stream.CopyTo(filestream);
            //}
        }
    }

我也尝试过从设备设置标志 link

如何为我的应用定义分区存储？

任何更新如何在我的下载目录中下载 PDF 文件？

谢谢。

Answer 1

How can I define scoped storage for my app ?Any update how can I download PDF file in my downloads directory ?

Android 10 为应用程序引入了一种新的存储模式，称为范围存储，它改变了应用程序在设备外部存储上存储和访问文件的方式。如果您的目标是 Android 10（API 级别 29）或更高，请在应用的清单文件中将 requestLegacyExternalStorage 的值设置为 true。

<application android:requestLegacyExternalStorage="true" android:label="FormsSample.Android" android:theme="@style/MainTheme"></application>

然后在访问下载文件夹之前请求运行时写入和读取 EXTERNAL_STORAGE 权限。

public void requestpermission()
{
    if (ContextCompat.CheckSelfPermission(this, Manifest.Permission.WriteExternalStorage) != (int)Permission.Granted)
    {
        ActivityCompat.RequestPermissions(this, new string[] { Manifest.Permission.WriteExternalStorage }, 1);
    }


    if (ContextCompat.CheckSelfPermission(this, Manifest.Permission.ReadExternalStorage) != (int)Permission.Granted)
    {
        ActivityCompat.RequestPermissions(this, new string[] { Manifest.Permission.ReadExternalStorage }, 1);
    }
}

在 Xamarin.Forms 共享代码中创建接口 IAccessFileService。

public interface IAccessFileService
{
    void CreateFile(string FileName);
}

在 Android platform.You 上实现 IAccessFileService 接口可以使用 File.Exists(xx) 检查文件夹是否存在，如果不存在则使用 Directory.CreateDirectory(xx) 创建文件夹。

[assembly: Xamarin.Forms.Dependency(typeof(AccessFileImplement))]
namespace FormsSample.Droid
{
    public class AccessFileImplement : IAccessFileService
    {
        public void CreateFile(string FileName)
        {
            string text = "hello world";
            byte[] data = Encoding.ASCII.GetBytes(text);
            string rootPath = Path.Combine(Android.OS.Environment.ExternalStorageDirectory.AbsolutePath, Android.OS.Environment.DirectoryDownloads);
            var filePathDir = Path.Combine(rootPath, "folder");
            if (!File.Exists(filePathDir))
            {
                Directory.CreateDirectory(filePathDir);
            }
            string filePath = Path.Combine(filePathDir, FileName);
            File.WriteAllBytes(filePath, data);
        }

        
    }
}

所以使用 dependencyservice 调用 android CreateFile 方法。

private void btn1_Clicked(object sender, EventArgs e)
{
    DependencyService.Get<IAccessFileService>().CreateFile("test.txt");
}

Answer 2

几个月前我遇到了同样的问题。

我在 developer.android 页面上找到了这个： (https://developer.android.com/reference/android/os/Environment#getExternalStorageDirectory())

第一个替代方案 (getExternalFilesDir) 无法正常工作，文件不会出现在下载目录中，此位置在应用程序内部。

第二种选择是媒体文件。

我最终使用了第三种选择。我在 Android 项目中创建了一个服务 class，像这样：

public class FilesManager : IFilesManager
{
    private const int CREATE_FILE_REQUEST_CODE = 123;
    private static Context _context;
    
    public static void Init(Context context)
    {
        _context = context;
    }

    public async Task SaveFile(string fileName, byte[] content)
    { 
        Intent intent = new Intent(Intent.ActionCreateDocument);
        intent.AddCategory(Intent.CategoryOpenable);
        intent.SetType(your_file_mimeType);
        intent.PutExtra(Intent.ExtraTitle, fileName);

        var activity = (MainActivity)_context;
        var listener = new ActivityResultListener(activity);
        activity.StartActivityForResult(intent, CREATE_FILE_REQUEST_CODE);

        var result = await listener.Task;

        if (result == null)
        {
            // Cancelled by user
            return;
        }

        using (Stream os = _context.ContentResolver.OpenOutputStream(result.Data))
        {
            os?.Write(content);
            os?.Close();
        }
    }

    private class ActivityResultListener
    {
        private readonly TaskCompletionSource<Intent> Complete = new TaskCompletionSource<Intent>();
        public Task<Intent> Task { get { return this.Complete.Task; } }

        public ActivityResultListener(MainActivity activity)
        {
            // subscribe to activity results
            activity.ActivityResult += OnActivityResult;
        }

        private void OnActivityResult(int requestCode, Result resultCode, Intent data)
        {
            if(requestCode != CREATE_FILE_REQUEST_CODE)
            {
                return;
            }

            // unsubscribe from activity results
            var activity = (MainActivity)_context;
            activity.ActivityResult -= OnActivityResult;

            // process result
            if (resultCode == Result.Ok)
            {
                Complete.TrySetResult(data);
            }
            else
            {
                Complete.TrySetResult(null);
            }
        }
    }
}

在MainActivity.cs中添加：

public event Action<int, Result, Intent> ActivityResult;

protected override void OnActivityResult(int requestCode, Result resultCode, Intent data) 
{
    ActivityResult?.Invoke(requestCode, resultCode, data); 
}

可以在Forms.Init之后调用Init方法：

FilesManager.Init(this);

注意：此方法需要用户交互。系统将提示用户选择保存文件的位置。

Xamarin.Forms - 如何为 android 定义分区存储以及如何将其实现到下载目录中的下载文件？

Xamarin.Forms - How to define scoped storage for android and how can I implement it to downlaod files in Downloads directory?

android

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