.Net Maui Accessing Files And Folders Cross Platform Complete Guide

Prerequisites

1. Visual Studio: Install the latest version of Visual Studio with the .NET Multi-platform App UI development workload.
2. New .NET MAUI Project: Create a new project by selecting "Blazor Hybrid App (.NET MAUI)" or "MAUI App (.NET MAUI)".

Step 1: Setup File System Permissions

Before you can access files and folders, you must set up appropriate permissions.

Android:

Edit the AndroidManifest.xml file to include the required permissions:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.your_package_name">
    <!-- Requested permissions -->
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
</manifest>

For Android 10 and above, add the following attribute inside the <application> tag:

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

iOS/macOS:

Edit the Info.plist file to request permissions:

<key>NSAppleMusicUsageDescription</key>
<string>This app needs access to your music library to play tracks.</string>

<key>NSDocumentsFolderUsageDescription</key>
<string>This app needs access to your documents folder to save files.</string>

<key>NSLibraryFolderUsageDescription</key>
<string>This app needs access to your library folder to read files.</string>

Windows:

Windows does not require additional permissions for accessing files within the app's sandbox.

Step 2: Create a Simple Layout

We'll create a simple Blazor component to display file details and allow file picking.

Create a new Blazor component named FileAccess.razor with the following layout:

@page "/file-access"
<PageTitle>File Access</PageTitle>

<button @onclick="PickFile">Pick a File</button>
@if (file != null)
{
    <p>Picked File: @file.FileName</p>
    <p>Size: @file.Size bytes</p>
    <p>Path: @file.Path</p>
}

<button @onclick="ReadFileContent">Read File Content</button>
@if (fileContent != null)
{
    <pre>@fileContent</pre>
}

<button @onclick="SaveFile">Save Text to File</button>
<p>File will be saved to: @saveFilePath</p>

Step 3: Add Code to Pick a File

To pick a file, you can use the Microsoft.Maui.Storage.FilePicker service. This service provides a platform-independent way to pick files from the device's file system.

Add the following code to the FileAccess.razor component:

@using Microsoft.Maui.Storage;
@code {
    FileResult file;
    private string fileContent;
    private string saveFilePath;

    async Task PickFile()
    {
        var options = new PickOptions
        {
            PickerTitle = "Please select a text file",
            FileTypes = new[]
            {
                new FileType(
                    description: "TXT",
                    extensions: new[] { ".txt" })
            }
        };
        file = await FilePicker.Default.PickAsync(options);
    }

    private async Task ReadFileContent()
    {
        if (file != null)
        {
            var stream = await file.OpenReadAsync();
            using (var reader = new StreamReader(stream))
            {
                fileContent = await reader.ReadToEndAsync();
            }
        }
        else
        {
            fileContent = "No file picked.";
        }
    }

    private async Task SaveFile()
    {
        string content = "Hello, .NET MAUI!";
        string fileName = "example.txt";

        saveFilePath = Path.Combine(FileSystem.Current.CacheDirectory, fileName);

        try
        {
            using (var writer = FileSystem.Current.GetFileFromPathAsync(saveFilePath).Result.CreateText())
            {
                await writer.WriteLineAsync(content);
            }
            fileContent = "File saved successfully.";
        }
        catch (Exception ex)
        {
            fileContent = $"Error saving file: {ex.Message}";
        }
    }
}

Explanation:

• PickFile: Displays a picker to select a .txt file.
• ReadFileContent: Reads the content of the picked file.
• SaveFile: Saves some text content to a file in the Cache directory.

Step 4: Handle Different Platforms

While the file picker and reading/writing functionality are cross-platform, how you handle file paths might differ slightly based on the platform. .NET MAUI provides FileSystem.AppDataDirectory and FileSystem.CacheDirectory which are common locations for storing data.

private string GetSaveFilePath()
{
    string filename = "example.txt";
    // Platform-specific logic can be added here if needed.
    return Path.Combine(FileSystem.Current.CacheDirectory, filename);
}

In this example, we used FileSystem.Current.CacheDirectory for simplicity.

Step 5: Testing Your Application

Now that the code is set up, run your application in Visual Studio.

1. Pick a File: Click the "Pick a File" button to open the file picker dialog. Select a .txt file and display its properties.
2. Read File Content: Click the "Read File Content" button to display the content of the picked file.
3. Save File: Click the "Save Text to File" button to save some text to a file in the Cache directory.

Ensure that you grant the necessary permissions when prompted.

Example of Complete Code

Here's the complete code in the FileAccess.razor file:

@page "/file-access"
<PageTitle>File Access</PageTitle>

<button @onclick="PickFile">Pick a File</button>
@if (file != null)
{
    <p>Picked File: @file.FileName</p>
    <p>Size: @file.Size bytes</p>
    <p>Path: @file.Path</p>
}

<button @onclick="ReadFileContent">Read File Content</button>
@if (fileContent != null)
{
    <pre>@fileContent</pre>
}

<button @onclick="SaveFile">Save Text to File</button>
<p>File will be saved to: @saveFilePath</p>

@code {
    FileResult file;
    private string fileContent;
    private string saveFilePath;

    async Task PickFile()
    {
        var options = new PickOptions
        {
            PickerTitle = "Please select a text file",
            FileTypes = new[]
            {
                new FileType(
                    description: "TXT",
                    extensions: new[] { ".txt" })
            }
        };
        file = await FilePicker.Default.PickAsync(options);
    }

    private async Task ReadFileContent()
    {
        if (file != null)
        {
            var stream = await file.OpenReadAsync();
            using (var reader = new StreamReader(stream))
            {
                fileContent = await reader.ReadToEndAsync();
            }
        }
        else
        {
            fileContent = "No file picked.";
        }
    }

    private async Task SaveFile()
    {
        string content = "Hello, .NET MAUI!";
        string fileName = "example.txt";

        saveFilePath = Path.Combine(FileSystem.Current.CacheDirectory, fileName);

        try
        {
            using (var writer = FileSystem.Current.GetFileFromPathAsync(saveFilePath).Result.CreateText())
            {
                await writer.WriteLineAsync(content);
            }
            fileContent = "File saved successfully.";
        }
        catch (Exception ex)
        {
            fileContent = $"Error saving file: {ex.Message}";
        }
    }
}

Conclusion

You now have a basic understanding of how to access files and folders in .NET MAUI. The key points to remember are setting up permissions in each platform's configuration, and using Microsoft.Maui.Storage for cross-platform file operations.