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# Accordion
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An expand/collapse panel list. Items are collapsed by default; one item can be pre-expanded at server render time. Client-side toggle is handled by `components.js`.
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---
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## HTML structure
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```
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div.accordion-root[id] ← outer wrapper
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div.accordion-item ← one per item, border-b separator
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h3
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button.accordion-trigger ← clickable header; aria-expanded tracks state
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{title text}
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svg.accordion-chevron ← rotates 180° when open
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div.accordion-panel ← collapsible area; height/opacity driven by JS
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div.pb-4
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{content}
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```
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---
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## CSS mechanics
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| Class / property | Effect |
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|---|---|
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| `overflow-hidden` on panel | Prevents content leaking outside the panel during animation |
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| `transition-all duration-200` on panel | Smooth height and opacity animation |
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| `height: 0; opacity: 0` (collapsed) | Starting state set server-side for closed items |
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| `height: auto; opacity: 1` (open) | Starting state for the pre-expanded item |
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| `accordion-chevron` + JS `rotate(180deg)` | Chevron rotates down when expanded |
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---
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## JavaScript (`initAccordion` in `components.js`)
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Runs on `DOMContentLoaded` and on `htmx:afterSwap` so HTMX-swapped accordions are correctly initialized.
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**Per-instance initialization:**
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1. Guard `root._accInitialised` prevents double-binding after re-renders
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2. For each `.accordion-trigger`, attach a `click` listener:
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- Read current state from `aria-expanded`
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- If currently open → set `panel.style.height = "0"`, `opacity = "0"`, `aria-expanded = "false"`
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- If currently closed → set `panel.style.height = scrollHeight + "px"`, `opacity = "1"`, `aria-expanded = "true"`
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3. Rotate `.accordion-chevron` via `transform: rotate(180deg)` when open
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---
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## Constructor signature
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```csharp
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public Accordion(
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string id,
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IEnumerable<(string Title, string Content)> items,
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int openIndex = -1)
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```
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| Parameter | Description |
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|---|---|
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| `id` | Unique element id for the root `div` |
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| `items` | List of `(Title, Content)` tuples |
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| `openIndex` | Zero-based index of the pre-expanded item; `-1` = all closed |
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---
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## Usage examples
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### All closed
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```csharp
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new Accordion(
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id: "faq",
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items: new[]
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{
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("What is this?", "A fast HTMX app framework."),
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("Is it AOT-safe?", "Yes, fully."),
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("Do I need Node?", "Only to run the Tailwind build step."),
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})
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```
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### One pre-expanded
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```csharp
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new Accordion(
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id: "setup-steps",
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items: new[]
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{
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("Step 1 — Install", "Run <code>npm install</code> in the project folder."),
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("Step 2 — Configure", "Edit <code>appsettings.json</code> with your connection string."),
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("Step 3 — Run", "Use <code>dotnet run</code> to start the server."),
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},
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openIndex: 0)
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```
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### HTML content in items
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```csharp
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new Accordion(
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id: "code-examples",
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items: new[]
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{
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("C# snippet", "<pre><code>var x = 1 + 1;</code></pre>"),
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("Tip", "<p>Use <strong>AOT-safe</strong> serialization patterns.</p>"),
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})
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```
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---
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## Tips and tricks
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- `openIndex` only controls the initial server-rendered state. After the page loads, the user can open/close any item freely.
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- Item `Title` and `Content` strings are inserted as raw HTML — HTML-encode any user-supplied values before passing them in.
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- Multiple items can be opened simultaneously by the user — there is no "only one open at a time" constraint in the JS.
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- If you need to identify which accordion is which after a click, listen to the parent element and inspect `event.target.closest('.accordion-item')`.
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- The `id` must be unique on the page if you place more than one accordion.
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---
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## Complete page example
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**`Templates/FaqPage.htmx`**
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```html
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<div class="max-w-2xl mx-auto py-10">
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<h1 class="text-2xl font-bold mb-2">Frequently Asked Questions</h1>
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<p class="text-muted-foreground mb-8">Everything you need to know about BeepBoop.</p>
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$$FaqAccordion$$
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</div>
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```
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**`Templates/FaqPage.htmx.cs`**
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```csharp
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namespace Htmx.ApiDemo.Templates;
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public sealed class FaqPage : FaqPageBase
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{
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private readonly IHtmxComponent _faq;
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public FaqPage()
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{
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_faq = new Components.Accordion(
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id: "faq",
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items: new[]
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{
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("What is BeepBoop?",
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"A fast, AOT-safe HTMX web framework built on .NET 10."),
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("Do I need Node.js?",
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"Only to run the Tailwind CSS build step during development."),
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("Is MongoDB required?",
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"No — swap in any data store you prefer."),
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("How do I deploy?",
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"Run <code>dotnet publish -c Release</code> for a native AOT binary."),
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});
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}
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protected override void RenderFaqAccordion(HtmxRenderContext ctx)
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=> _faq.Render(ctx.Next());
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}
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```
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**`Templates/FaqPage.htmx.cs` — GET handler**
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```csharp
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[Handler]
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[MapGet("/faq")]
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public static partial class GetFaqHandler
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{
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public record Query();
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private static Task<IResult> HandleAsync(
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Query _,
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HttpContext ctx,
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CancellationToken ct)
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=> ctx.WriteHtmxPage(new FaqPage(), title: "FAQ");
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}
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```
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Reference in New Issue
Block a user