Xamarin forms: How to create folder and a file in device external storage?

Question

I am trying to create a folder and a text file in that folder on the device's external storage. The same as WhatsApp does. Also, I need to write some data to that file.

Is it possible to do this in xamarin forms? Or should we need to use a dependency service?

Thanks in advance

Answer 1

I tried this but getting System.UnauthorizedAccessException: 'Access to the path "/storage/emulated/0/Download/myfile.txt" is denied

Hi, @Sreejith Sree . Android 10 introduced a new storage paradigm for apps called scoped storage which changes the way apps store and access files on a device's external storage. If you target Android 10 (API level 29) or higher, set the value of android:requestLegacyExternalStorage to true in your app's manifest file.

Check the doc: https://developer.android.com/training/data-storage/use-cases#opt-out-scoped-storage

I need a create a folder first, then a text file on that folder

You could use File.Exists(xx) to check if the folder exists, and use Directory.CreateDirectory(xx) to create the folder if not. Check the code:

   [assembly: Xamarin.Forms.Dependency(typeof(AccessFileImplement))]  
   namespace TestApplication.Droid  
   {  
       public class AccessFileImplement : IAccessFileService  
       {  
           void IAccessFileService.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);  
           }  
       }  
   }  

Answer 2

Hello,​

Welcome to our Microsoft Q&A platform!

I am trying to create a folder and a text file in that folder on the device's external storage ... should we need to use a dependency service?

The File class provides the related method to create, delete, and read files in the shared project, but it can only access the application folder.

   File.WriteAllText(fileName, text);  
   string text = File.ReadAllText(fileName);  

To create a file in the external storage, try to achieve the function on the native platform using DependencyService.

   //1.create an interface to define the method  
   public interface IAccessFile  
   {  
       void CreateFile(string FileName);  
   }  
     
   //2.implement the service on the android platform  
   [assembly: Xamarin.Forms.Dependency(typeof(AccessFileImplement))]  
   namespace XamarinFirebase.Droid  
   {  
       public class AccessFileImplement : IAccessFile  
       {  
     
     
           void CreateFile(string FileName)  
           {  
               string text = "xxx";  
               byte[] data = Encoding.ASCII.GetBytes(text);  
               string DownloadsPath = Path.Combine(Android.OS.Environment.ExternalStorageDirectory.AbsolutePath, Android.OS.Environment.DirectoryDownloads);  
               string filePath = Path.Combine(DownloadsPath, FileName);  
               File.WriteAllBytes(filePath, data);  
           }  
       }  
   }  
     
   //3.consume the DependencyService command in the shared project  
   DependencyService.Get<IAccessFile>().CreateFile("myfile.txt");  

It cannot be available on iOS platform, iOS imposes some restrictions on what an application can do with the file system to preserve the security of an application’s data.
An application is limited to reading and writing files within its home directory (installed location); it cannot access another application’s files.

Related tutorials:
https://learn.microsoft.com/en-us/xamarin/android/platform/files/external-storage?tabs=windows
https://learn.microsoft.com/en-us/xamarin/ios/app-fundamentals/file-system#special-considerations

Best Regards,

Jarvan Zhang

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