PatrickJahr.Blazor.FileHandling 1.0.0

PatrickJahr.Blazor.FileHandling

Introduction

A Blazor wrapper for the File Handling API.

The File Handling API allows you to register your Progressive Web App as a file handler for certain file types.

Getting started

Prerequisites

You need .NET 7.0 or newer to use this library.

Download .NET 7 Download .NET 8

Platform support

Platform support for Badging API

Installation

You can install the package via NuGet with the Package Manager in your IDE or alternatively using the command line:

dotnet add package PatrickJahr.Blazor.FileHandling

Usage

The package can be used in Blazor WebAssembly projects.

Add to service collection

To make the FileHandlingService available on all pages, register it at the IServiceCollection in Program.cs before the host is built:

builder.Services.AddFileHandlingService();

Checking for browser support

Before using the File Handling API, you should first test if the API is supported on the target platform by calling the IsSupportedAsync() method. This method returns a boolean to indicate whether the File Handling API is supported or not.

var isSupported = await fileHandlingService.IsSupportedAsync();
if (isSupported)
{
    // enable file handling feature
}
else
{
    // use fallback mechanism or hide/disable feature
}

Internally, this method tests for the presence of the launchQueue property on the window object of the target browser.

Register in Web App Manifest

The API consists of two parts: First, you need to declare support for the target file types in your Web Application Manifest (typically called manifest.json or manifest.webmanifest). The property file_handlers contains an array of file handlers. Each file handler consists of the list of accepted media types and file extensions (accept property). The action property contains the address that should be launched when a file with the particular media type or file extension was opened.

{
  "file_handlers": [
    {
      "action": "./",
      "accept": {
        "text/plain": [".txt"]
      }
    }
  ]
}

During installation, the application is registered at the target platform as a handler for the given file types.

Access launch parameters during runtime

To access the launch parameters during runtime, call the SetConsumerAsync() method. This method takes an action that is immediately called with the LaunchParams. This object has a Files property that currently directly contains a list of FileSystemHandles for the files. The handles are either an instance of FileSystemFileHandle or FileSystemDirectoryHandle, so make sure to check for the correct type. To get the binary contents of files, call the GetFileAsync() method on a FileSystemFileHandle. This method returns a File object that offers methods like TextAsync() and ArrayBufferAsync() to retrieve the file's contents in different formats.

var isSupported = await fileHandlingService.IsSupportedAsync();
if (isSupported)
{
    await _fileHandlingService.SetConsumerAsync(async (launchParams) =>
    {
        foreach (var fileSystemHandle in launchParams.Files)
        {
            if (fileSystemHandle is FileSystemFileHandle fileSystemFileHandle)
            {
                var file = await fileSystemFileHandle.GetFileAsync();

                var text1 = await file.TextAsync();
                Console.WriteLine(text1);

                var bytes = await file.ArrayBufferAsync();
                var text2 = System.Text.Encoding.UTF8.GetString(bytes);
                Console.WriteLine(text2);
            }
        }
    });
}

Related articles

• WICG Specification (file_handlers member)
• WICG Specification (launch queue)
• Blog post on web.dev
• Browser support on caniuse.com

Acknowledgements

Thanks to Kristoffer Strube who provides a Blazor wrapper for the File System Access API. This library is inspired by Kristoffer's implementation and project setup, and uses the same classes to access file contents.

License and Note

BSD-3-Clause.

This is a technical showcase, not an official PatrickJahr product.