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An MSBuild package which adds simple PWA functionality to Blazor client-side Apps
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README.md

Blazor PWA Builder - MSBuild

The easiest way to turn your Server Side And Client Side Blazor projects into Progressive Web Apps (PWA).

This project, when added to your build process, will generate the required files to enable basic PWA abilities for your project.

It generates a manifest.json, a Service Worker with pre-caching of all required files (Blazor WebAssembly only) and an installer for the Service Worker.

It currently includes a simple banner, by default, to notify the user that your application can be installed, and a simple alert to notify users when your application has been updated (CSB Only).

This is now an official release - I am looking for feedback/issues/requests.

Browser compatibility

Note that chromium browsers will prompt you to install a PWA on a desktop computer. Firefox does not currently provide this experience on desktop. I don't have a Mac, but I believe Safari does not prompt on desktop either.

Installation

Install the nuget BlazorPWA.MsBuild

Package Manager:

Install-Package BlazorPWA.MSBuild -Version 1.0.1

.NET Cli:

dotnet add package BlazorPWA.MSBuild --version 1.0.1

Package Reference

<PackageReference Include="BlazorPWA.MSBuild" Version="1.0.1"/>

Configuration

Required configuration: none *.

*Really! try it!

This PWA builder is constructed using MSBuild targets, which get installed in your .nuget cache.

You are free to inspect those targets and customise any part of the build by adding Properties to your csproj, or to a .props file in the source tree.

For example, by default, the PWA builder will only generate the PWA files once, which means, should you want to, you can add it to your project, build once - you will have the required files for a PWA and will be free to modify them to suit.

Should you want to re-generate the PWA files every build, you can add this Property to your csproj

<ServiceWorkerForce>true</ServiceWorkerForce>

When you want to publish an update to your app, you may need to supply a new browser cache version - if you don't change anything in the Service Worker the end user will not use your new code!

Note: PWAs update when they detect a change in the Service Worker code - this cache version number is used in the Service Worker, so updating the cache version number will trigger an update of the PWA for the end user. It's also important as the cache is where your code is stored - if you don't update the cache version, it will not refresh with your new code

<ServiceWorkerCacheVersion>2</ServiceWorkerCacheVersion>

The web manifest has properties for the application name, which are taken, by default, from your project and solution names, but you can override them

<ManifestShortName>My Project</ManifestShortName>

<ManifestLongName>My Really Great Project</ManifestLongName>

There are dozens of Properties in the targets files supplied by this package - you could customise them all, but you probably don't need to, so proceed with caution.

Handing the "Installable PWA" event in Blazor

When a Chromium based browser detects an installable PWA, it fires an event that your application can use to display a prompt to the user.

The default for this package is to simply display a bar at the bottom of the browser window prompting the user to install your app.

You can customise the message, or you can override that and pass the event over to your Blazor application - by setting the property ServiceWorkerRegisterInstallableType to installable-blazor in your .csproj

This will generate code in your ServiceWorkerRegister.js to make an interop call to Blazor when the beforeinstallprompt event fires in the browser.

In your Blazor application, you will need code to handle this call

  • by default it will use the ProjectName and method name "InstallPWA" to perform a DotNet.InvokeAsync()
  • These values can be customised using the properties ServiceWorkerBlazorAssembly and ServiceWorkerBlazorInstallMethod

Here is an example Blazor implementation which could be added to MainLayout

@if (Installable)
{
    <div class="fixed-bottom w-100 alert alert-dark d-flex align-items-center" @onclick="InstallClicked">
        <h3>Install this app?</h3>
        <small class="ml-auto mr-1 rounded-pill"><button @onclick="@(()=>Installable=false)">X</button></small>
    </div>
}

This will display a bar at the bottom of the browser, which can be dismissed or clicked.

The code section has the JSInvokable method InstallPWS that we called earlier from the browser and some supporting code to toggle the display and make an interop call back to the browser to trigger the app installation.

@code
{
    [Inject] IJSRuntime JSRuntime { get; set; }

    static bool Installable = false;
    static Action ml;
    protected override void OnInitialized()
    {
        ml = () => InvokeAsync(StateHasChanged);
    }
    [JSInvokable]
    public static Task InstallPWA()
    {
        Installable = true;
        ml.Invoke();
        return Task.CompletedTask;
    }
    Task InstallClicked(UIMouseEventArgs args)
    {
        Installable = false;
        return JSRuntime.InvokeAsync<object>("BlazorPWA.installPWA");
    }
}

Excluding files from the cache (WebAssembly projects)

Due to the way Blazor WebAssembly projects build, some of the required properties we use to generate a PWA are not available until post-build.

So, to ensure a smooth customisation, we recommend using a custom Target in your csproj (or as a separate file which you include in the build process).

There are two Properties that you can customise to exclude files from the cache.

  • ServiceWorkerPreCacheExcludeFiles - by default this will exclude any files under dist\_content and any files in WWWRoot that start with a dot. File patterns listed here will be evaluated after build and excluded from the Service Worker cache. This property is used in both Debug and Release builds.

  • ServiceWorkerPreCacheExcludeReleaseFiles - by default this will exclude any .pdb files. This property is only used if you are building in Release mode.

You can add extra files to these Properties by adding a custom target to your project

  <Target Name="PWACustomise" BeforeTargets="CreatePWA">
    <PropertyGroup>
      <ServiceWorkerPreCacheExcludeFiles>
        $(OutputPath)dist\_redist\**\*.*;
      </ServiceWorkerPreCacheExcludeFiles>
    </PropertyGroup>
    <Message Importance="high" Text="Removing: $(ServiceWorkerPreCacheExcludeFiles)"/>
  </Target>

The Name can be anything you like, but is required by MSBuild.

$(OutputPath)dist is the path to the distribution folder for a Blazor WebAssembly build.

So, this example is excluding all files under the _redist folder from the Service Worker Cache.

Prevent PWA installation / caching on localhost (or any host)

If you want to exclude localhost (or any host) so that the developer inner loop is not affected, you can now use the ServiceWorkerIgnoreHosts property.

Add it to you csproj file under PropertyGroup and list the hosts you want to exclude.

  <PropertyGroup>
    <ServiceWorkerIgnoreHosts>'localhost','127.0.0.1','::1','KarensPC'</ServiceWorkerIgnoreHosts>
  </PropertyGroup>

The service worker will not register itself when the hostname matches anything in the list.

Note: the single quotes around each hostname are required for now

Roadmap

  • At the moment, there is only one choice for caching strategy - Cache First/Network Fallback - I will add more (https://developers.google.com/web/ilt/pwa/introduction-to-progressive-web-app-architectures#caching_strategies_supported_by_sw-toolbox)
  • The current method for alerting the user that the app is installable is semi-hard coded (you can adjust it manually after generation) - this will change to allow hooks/callbacks into Blazor via project properties
  • The current method for alerting the user when an update is available is semi-hard coded (you can adjust it manually after generation) - this will change to allow hooks/callbacks into Blazor via project properties
  • Document all of the configuration Properties (they all have comments in the code - so you are able to understand their purpose without documentation...)
  • Bug fixes
  • Allow hosts exclusions - so working on localhost can avoid PWA caching

Contribute

Please feel free to create issues, ask questions and submit Pull Requests.

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