Problem with DependencyService in .NET MAUI for iOS: Cannot get an instance of IFileHelper, always return null

Question

I'm working on a .NET MAUI application that uses DependencyService to get the local path to a file on iOS. Although I have followed the instructions to correctly register my IFileHelper implementation, I always get an exception stating that an IFileHelper instance cannot be obtained.

Code in the Shared Project

IFileHelper.cs:

namespace App7.Clases.BasesDatos

{

public interface IFileHelper

{

string GetLocalFilePath(string filename);

}

}

The code jumps directly to the catch block and does not get the file path, DependencyService always return null

ResultadosBD.cs:

using System;

using System.IO;

using Microsoft.Maui.Controls;

namespace App7.Clases.BasesDatos

{

public partial class ResultadosBD : ContentPage

{

private readonly DatosRepository? _datosRepository;

public ResultadosBD()

{

InitializeComponent();

try

{

var fileHelper = DependencyService.Get<IFileHelper>();

if (fileHelper == null)

{

throw new Exception("No se pudo obtener una instancia de IFileHelper.");

}

string databasePath = fileHelper.GetLocalFilePath("OMSAnthroP.db3");

if (File.Exists(databasePath))

{

Console.WriteLine($"El archivo de base de datos existe en la ruta: {databasePath}");

}

else

{

Console.WriteLine($"El archivo de base de datos no existe en la ruta: {databasePath}");

CreateDatabaseFile(databasePath);

Console.WriteLine($"Archivo de base de datos creado en la ruta: {databasePath}");

}

try

{

// Inicializar el repositorio de datos

_datosRepository = new DatosRepository(databasePath);

}

catch (Exception ex)

{

Console.WriteLine($"Error al inicializar el repositorio de datos: {ex.Message}");

}

}

catch (Exception ex)

{

Console.WriteLine($"Error al obtener la ruta del archivo: {ex.Message}");

}

}

private void CreateDatabaseFile(string path)

{

// Implementa la lógica para crear el archivo de base de datos aquí

}

}

}

FileHelper.cs:

using System;

using System.IO;

using Foundation;

using App7.Clases.BasesDatos;

using Microsoft.Maui.Controls;

[assembly: Dependency(typeof(App7.iOS.FileHelper))]

namespace App7.iOS

{

public class FileHelper : IFileHelper

{

public string GetLocalFilePath(string filename)

{

string downloadPath;

NSFileManager fileManager = NSFileManager.DefaultManager;

NSUrl[] urls = fileManager.GetUrls(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomain.User);

if (urls != null && urls.Length > 0 && urls[0] != null)

{

downloadPath = urls[0].Path ?? throw new Exception("El Path de la URL es nulo.");

}

else

{

throw new Exception("No se pudo obtener el directorio de documentos de la aplicación.");

}

return Path.Combine(downloadPath, filename);

}

}

}

What could be causing DependencyService.Get<IFileHelper>() to always return null in my .NET MAUI for iOS application?

Thanks in advance for any help you can provide.

Answer 1

Hello,

With MAUI, you could invoke platform code instead of DependencyService, and use conditional compilation to target different platforms.

For example, I invoke the code in MainPage directly, please refer to the following code:

(You could also try Environment.SpecialFolder.MyDocuments to get the Document path. Besides, you could try FileSystem.AppDataDirectory to save the file in Library folder, see File system helpers - .NET MAUI | Microsoft Learn）

private void OnCounterClicked(object sender, EventArgs e)
        {
#if IOS
            string databasePath = this.GetLocalFilePath("OMSAnthroP.db3");// your GetLocalFilePath method
            var path = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments), "OMSAnthroP.db3");// you could call this to find Document folder
           //var path = Path.Combine(FileSystem.AppDataDirectory, "OMSAnthroP.db3");
#endif
        }
 
 
#if IOS
        public string GetLocalFilePath(string filename)
        {
            string downloadPath;
            NSFileManager fileManager = NSFileManager.DefaultManager;
            NSUrl[] urls = fileManager.GetUrls(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomain.User);
            if (urls != null && urls.Length > 0 && urls[0] != null)
            {
                downloadPath = urls[0].Path ?? throw new Exception("El Path de la URL es nulo.");
            }
            else
            {
                throw new Exception("No se pudo obtener el directorio de documentos de la aplicación.");
            }
            return Path.Combine(downloadPath, filename);
        }
 
#endif

Best Regards,

Wenyan Zhang

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