---license: MITname: author-componentdescription: >USE FOR: writing new Blazor components that do NOT involve JavaScript interop,DO NOT USE FOR: creating new projects (use create-blazor-project), JavaScript---

Author Blazor Component

Core Rules

• Data flows down via [Parameter]. Events flow up via EventCallback<T> (never Action/Func).
• Never mutate [Parameter] properties. Copy to a private field in OnParametersSet.
• Use [Parameter] public T Prop { get; set; } — never required or init (causes BL0007).
• Use [EditorRequired] for required parameters.
• Handle all states: loading, empty, loaded, error — each with @if/@else.
• Use @key on repeated elements in loops for efficient diffing.
• Use IReadOnlyList<T> (not IEnumerable<T>) for collection parameters.

RenderFragment & Generics

[Parameter] public RenderFragment? ChildContent { get; set; }
[Parameter] public RenderFragment<TItem>? RowTemplate { get; set; }  // generic template

Use @typeparam TItem for generic components.

File Patterns

• Single-file: .razor with @code block when logic < ~50 lines.
• Code-behind: .razor + .razor.cs with partial class when logic > ~50 lines.

Disposal

Implement IAsyncDisposable (not IDisposable) when the component owns subscriptions, timers, or CTS. In DisposeAsync: unsubscribe (-=), cancel CTS, dispose resources. Never call StateHasChanged.

Async Patterns

• await every async operation. Never use .Result, .Wait(), Task.Run, ContinueWith, Thread.Start.
• Debounce: Task.Delay + CancellationTokenSource. Cancel old CTS, create new, await delay, do work. Never use System.Threading.Timer or System.Timers.Timer.
• Polling: Loop in OnInitializedAsync with await Task.Delay(interval, token) — stays on sync context.
• External events (Action<T>): Use async void handler + await InvokeAsync(() => { state++; StateHasChanged(); }) + catch → DispatchExceptionAsync. Never _ = InvokeAsync(...).
• Cancel CTS in DisposeAsync. Don't catch ObjectDisposedException — use CTS cancellation.

Don'ts

• required/init on [Parameter] — runtime failure
• Mutate [Parameter] — copy to private field in OnParametersSet
• Action/Func for events — use EventCallback<T>
• Task.Run/.Result/.Wait()/Timer for debounce — deadlock or thread-pool escape
• Inline style attributes — use CSS classes or data-* attributes
• catch { throw; } — use when guard or let exceptions propagate
• Gold-plating: ARIA, wrapper divs, accessibility features not requested
• _ = InvokeAsync(...) — swallows exceptions; use async void + DispatchExceptionAsync