Faster preview on no change, future hot reload #192
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| @using System.Reflection | ||
| @using TryMudBlazor.Client.Pages | ||
| @using TryMudBlazor.Client.Services | ||
| @implements IDisposable | ||
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| <Router AppAssembly="@typeof(Program).Assembly" | ||
| AdditionalAssemblies="@_additionalAssemblies" | ||
| NotFoundPage="typeof(NotFound)"> | ||
| <Found Context="routeData"> | ||
| <RouteView RouteData="@routeData" DefaultLayout="@typeof(EmptyLayout)" /> | ||
| </Found> | ||
| </Router> | ||
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| @code { | ||
| private readonly Assembly[] _additionalAssemblies; | ||
| private readonly IDisposable _subscription; | ||
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| public App(UserComponentsAssemblyService assemblyService) | ||
| { | ||
| _additionalAssemblies = [assemblyService.Assembly]; | ||
| _subscription = assemblyService.Subscribe(HandleAssemblyChanged); | ||
| } | ||
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| private Task HandleAssemblyChanged(Assembly assembly) | ||
| { | ||
| _additionalAssemblies[0] = assembly; | ||
| return InvokeAsync(StateHasChanged); | ||
| } | ||
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| public void Dispose() | ||
| { | ||
| _subscription.Dispose(); | ||
| } | ||
| } | ||
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| @@ -0,0 +1,32 @@ | ||
| using System.Reflection; | ||
| using Microsoft.AspNetCore.Components.WebAssembly.Hosting; | ||
| using Try.UserComponents; | ||
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| namespace TryMudBlazor.Client.Extensions; | ||
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| internal static class WebAssemblyHostBuilderExtensions | ||
| { | ||
| private static readonly MethodInfo ConfigureMethod = ResolveConfigureMethod(); | ||
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| public static void TryInvokeUserStartup(this WebAssemblyHostBuilder builder) | ||
| => ConfigureMethod?.Invoke(null, [builder]); | ||
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There was a problem hiding this comment. The ConfigureMethod is resolved once at static initialization and cached. If the UserComponents assembly is hot-reloaded with a different UserStartup class definition, the cached method will still point to the old assembly's method. Since UserStartup changes trigger a full reload (as seen in UserMainPage.razor lines 57-62), this is acceptable, but consider adding a comment explaining this limitation or the relationship to the hot reload logic.
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There was a problem hiding this comment. I tested it before commit, and tests showed it's all good. The startup doesn't get cached, and once i edit it everything is working as expected because full iframe reload happens on edit, and it will get new usercomponents and new TryInvokeUserStartup invocation |
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| private static MethodInfo ResolveConfigureMethod() | ||
| { | ||
| var assembly = typeof(__Main).Assembly; | ||
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| var startupType = | ||
| assembly.GetType("UserStartup", throwOnError: false, ignoreCase: true) ?? | ||
| assembly.GetType("Try.UserComponents.UserStartup", throwOnError: false, ignoreCase: true); | ||
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| var method = startupType?.GetMethod("Configure", BindingFlags.Static | BindingFlags.Public); | ||
| if (method is null) | ||
| return null; | ||
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| var parameters = method.GetParameters(); | ||
| if (parameters.Length != 1 || parameters[0].ParameterType != typeof(WebAssemblyHostBuilder)) | ||
| return null; | ||
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| return method; | ||
| } | ||
| } | ||
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| @@ -0,0 +1,4 @@ | ||
| @page "/not-found" | ||
| @layout EmptyLayout | ||
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| <p>Sorry, there's nothing at this address.</p> |
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| @@ -0,0 +1,91 @@ | ||||||||||||||||||
| @page "/__main" | ||||||||||||||||||
| @using Microsoft.JSInterop | ||||||||||||||||||
| @using System.Runtime.Loader | ||||||||||||||||||
| @using Try.UserComponents | ||||||||||||||||||
| @using TryMudBlazor.Client.Services | ||||||||||||||||||
| @inject IJSRuntime JSRuntime | ||||||||||||||||||
| @inject UserComponentsAssemblyService AssemblyService | ||||||||||||||||||
| @implements IAsyncDisposable | ||||||||||||||||||
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| <MudDialogProvider FullWidth="true" MaxWidth="MaxWidth.ExtraSmall" /> | ||||||||||||||||||
| <MudSnackbarProvider /> | ||||||||||||||||||
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| <DynamicComponent Type="@_type" /> | ||||||||||||||||||
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| @code { | ||||||||||||||||||
| private Type _type = typeof(__Main); | ||||||||||||||||||
| private AssemblyLoadContext _loadContext; | ||||||||||||||||||
| private readonly Lazy<DotNetObjectReference<UserMainPage>> _ref; | ||||||||||||||||||
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| public UserMainPage() | ||||||||||||||||||
| { | ||||||||||||||||||
| _ref = new Lazy<DotNetObjectReference<UserMainPage>>(CreateDotNetObject()); | ||||||||||||||||||
| } | ||||||||||||||||||
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| protected override async Task OnAfterRenderAsync(bool firstRender) | ||||||||||||||||||
| { | ||||||||||||||||||
| if (firstRender) | ||||||||||||||||||
| { | ||||||||||||||||||
| await JSRuntime.InvokeVoidAsync("Try.registerHotReload", _ref.Value); | ||||||||||||||||||
| } | ||||||||||||||||||
| } | ||||||||||||||||||
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| [JSInvokable] | ||||||||||||||||||
| public async Task HotReload() | ||||||||||||||||||
| { | ||||||||||||||||||
| try | ||||||||||||||||||
| { | ||||||||||||||||||
| var base64 = await JSRuntime.InvokeAsync<string>("sessionStorage.getItem", "TryMudBlazor.UserComponentsDllBase64"); | ||||||||||||||||||
| if (base64 == null) | ||||||||||||||||||
| { | ||||||||||||||||||
| // sessionStorage was cleared (e.g. crash recovery) — fall back to a full reload | ||||||||||||||||||
| // so loadBootResource picks up the safe static DLL. | ||||||||||||||||||
| await JSRuntime.InvokeVoidAsync("Try.requestFullReload", "/__main"); | ||||||||||||||||||
| return; | ||||||||||||||||||
| } | ||||||||||||||||||
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| var bytes = Convert.FromBase64String(base64); | ||||||||||||||||||
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| // Swap to a fresh collectible context; previous one becomes eligible for GC | ||||||||||||||||||
| // once Blazor disposes the old component instance below. | ||||||||||||||||||
| var previousContext = _loadContext; | ||||||||||||||||||
| _loadContext = new AssemblyLoadContext(name: null, isCollectible: true); | ||||||||||||||||||
| var assembly = _loadContext.LoadFromStream(new MemoryStream(bytes)); | ||||||||||||||||||
| previousContext?.Unload(); | ||||||||||||||||||
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There was a problem hiding this comment. The previous AssemblyLoadContext is unloaded immediately after loading the new assembly, but the old component instance that references types from the previous context may still be active at this point. The comment on line 49-50 suggests waiting for Blazor to dispose the old component, but the code doesn't actually wait. Consider moving the previousContext.Unload() call to after StateHasChanged completes, or use a delayed/queued unload mechanism to ensure the old component has been disposed first. This could lead to ObjectDisposedException or TypeLoadException when the old component tries to access its types during disposal. |
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| // UserStartup requires DI re-registration — fall back to full iframe reload | ||||||||||||||||||
| if (assembly.GetType("UserStartup") is not null || | ||||||||||||||||||
| assembly.GetType("Try.UserComponents.UserStartup") is not null) | ||||||||||||||||||
| { | ||||||||||||||||||
| await JSRuntime.InvokeVoidAsync("Try.requestFullReload", "/__main"); | ||||||||||||||||||
| return; | ||||||||||||||||||
| } | ||||||||||||||||||
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| var newType = assembly.GetType("Try.UserComponents.__Main"); | ||||||||||||||||||
| if (newType is not null) | ||||||||||||||||||
| { | ||||||||||||||||||
| // Update the Router's AdditionalAssemblies before rendering the new __Main | ||||||||||||||||||
| // so that any NavigateTo calls inside it can resolve user-defined @page routes. | ||||||||||||||||||
| await AssemblyService.UpdateAssemblyAsync(assembly); | ||||||||||||||||||
| _type = newType; | ||||||||||||||||||
| await InvokeAsync(StateHasChanged); | ||||||||||||||||||
| } | ||||||||||||||||||
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There was a problem hiding this comment. If the user's compiled assembly doesn't contain a
Suggested change
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There was a problem hiding this comment. This is impossible scenario |
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| } | ||||||||||||||||||
| catch | ||||||||||||||||||
| { | ||||||||||||||||||
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There was a problem hiding this comment. The catch block at line 74 swallows all exceptions without logging them. This makes debugging difficult when hot reload fails for unexpected reasons. Consider logging the exception before falling back to a full reload, especially during development. At minimum, log to the browser console using JSRuntime or Console.WriteLine.
Suggested change
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| await JSRuntime.InvokeVoidAsync("Try.requestFullReload", "/__main"); | ||||||||||||||||||
| } | ||||||||||||||||||
| } | ||||||||||||||||||
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There was a problem hiding this comment. If HotReload is called multiple times in quick succession (e.g., rapid user edits), there's a potential for race conditions. The _loadContext could be unloaded while a previous HotReload call is still processing, or _type could be updated mid-render. Consider adding a semaphore or checking if a reload is already in progress, and either queuing subsequent requests or ignoring them until the current reload completes.
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There was a problem hiding this comment. It's not called on users edits, for now. I prefer yagni here |
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| public async ValueTask DisposeAsync() | ||||||||||||||||||
| { | ||||||||||||||||||
| if (_ref.IsValueCreated) | ||||||||||||||||||
| { | ||||||||||||||||||
| await JSRuntime.InvokeVoidAsync("Try.unregisterHotReload"); | ||||||||||||||||||
| _ref.Value.Dispose(); | ||||||||||||||||||
| } | ||||||||||||||||||
| _loadContext?.Unload(); | ||||||||||||||||||
| } | ||||||||||||||||||
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| private DotNetObjectReference<UserMainPage> CreateDotNetObject() => DotNetObjectReference.Create(this); | ||||||||||||||||||
| } | ||||||||||||||||||
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The NotFoundPage property expects a Type, but it's being set to a string expression "typeof(NotFound)". This should be @typeof(NotFound) or simply typeof(NotFound) without quotes. As written, this will cause a compilation error since the Router component expects Type, not string.
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