# Slider

A draggable range control. Use it when you want the user to pick a numeric value within a range — volume, brightness, price range, font size.

---

## Quick example

```csharp
new Slider(
    id:    "volume",
    name:  "volume",
    label: "Volume")
```

Defaults to a 0–100 range with a starting value of 50.

---

## All the options

```csharp
public Slider(
    string id,
    string name         = "",
    int    min          = 0,
    int    max          = 100,
    int    step         = 1,
    int    value        = 50,
    string label        = "",
    string description  = "",
    string extraClasses = "",
    string hxAttrs      = "")
```

| Parameter | What it does |
|---|---|
| `id` | The element id. Also used by `<label for="...">`. |
| `name` | Form field name. |
| `min` | Lowest selectable value. |
| `max` | Highest selectable value. |
| `step` | How much the value changes per tick. |
| `value` | Starting position of the thumb. |
| `label` | Visible text label above the slider. |
| `description` | Small hint text below the slider. |
| `extraClasses` | Additional Tailwind classes on the `<input>`. |
| `hxAttrs` | Extra HTML attributes appended verbatim. |

---

## Real-world examples

### Brightness setting (stepped)

```csharp
new Slider(
    id:          "brightness",
    name:        "brightness",
    min:         10,
    max:         100,
    step:        10,
    value:       70,
    label:       "Brightness",
    description: "10 to 100")
```

### Font size with live HTMX update

```csharp
new Slider(
    id:      "fontSize",
    name:    "fontSize",
    min:     12,
    max:     32,
    value:   16,
    label:   "Font size",
    hxAttrs: """hx-post="/settings/font-size" hx-trigger="change"""")
```

### Reading the value in a form handler

```csharp
public record Command([property: FromForm] int Volume);
// command.Volume == 0..100
```

---

## How it works

Slider renders a native `<input type="range">`. The thumb and active track colour follow your primary theme colour via `accent-primary`. No JavaScript is needed — the browser handles the drag interaction natively.

```csharp
public record Command([property: FromForm] int Volume);

// command.Volume is the slider value at submit time
```

---

## Tips and tricks

- Display the current numeric value next to the slider by adding a small `<output>` element and a JS `input` event listener: `slider.addEventListener('input', e => output.value = e.target.value)`. This can be added via `hxAttrs: "oninput=\"document.getElementById('vol-val').textContent=this.value\""`.
- `value` is the **initial** server-rendered position. After the user moves the slider, only the form submission captures the new value.
- Use `step` to snap to meaningful increments (e.g. `step: 5` for a 0–100 percentage slider).
- `accent-primary` is supported in all modern browsers and requires no custom CSS.
- `accent-primary` is supported in all modern browsers and requires no custom CSS.

---

## Complete page example

**`Templates/AudioSettingsPage.htmx`**
```html
<div class="max-w-md mx-auto py-10">
  <h1 class="text-2xl font-bold mb-6">Audio settings</h1>
  <form method="post" action="/settings/audio">
    $$AntiforgeryToken$$
    <div class="space-y-6 mb-8">
      $$VolumeSlider$$
      $$BassSlider$$
      $$TrebleSlider$$
    </div>
    $$SaveBtn$$
  </form>
  $$SuccessAlert$$
</div>
```

**`Templates/AudioSettingsPage.htmx.cs`**
```csharp
namespace Htmx.ApiDemo.Templates;

public sealed class AudioSettingsPage : AudioSettingsPageBase
{
    private readonly IHtmxComponent _volume;
    private readonly IHtmxComponent _bass;
    private readonly IHtmxComponent _treble;
    private readonly IHtmxComponent _save;
    private readonly IHtmxComponent _success;
    private readonly byte[] _afToken;

    public AudioSettingsPage(
        IAntiforgery af,
        HttpContext ctx,
        AudioPrefs? prefs = null,
        bool saved = false)
    {
        var tokens = af.GetAndStoreTokens(ctx);
        _afToken = $"""<input type="hidden" name="{tokens.FormFieldName}" value="{tokens.RequestToken}">""".ToUtf8Bytes();

        _volume  = new Components.Slider(id: "volume",  name: "volume",  label: "Volume",  value: prefs?.Volume  ?? 70, description: "0 – 100");
        _bass    = new Components.Slider(id: "bass",    name: "bass",    label: "Bass",    value: prefs?.Bass    ?? 50, min: -10, max: 10, step: 1);
        _treble  = new Components.Slider(id: "treble",  name: "treble",  label: "Treble",  value: prefs?.Treble  ?? 50, min: -10, max: 10, step: 1);
        _save    = new Components.Button("Save", type: "submit");
        _success = saved ? new Components.Alert(title: "Audio settings saved.") : HtmxEmpty.Instance;
    }

    protected override void RenderAntiforgeryToken(HtmxRenderContext ctx) => ctx.Writer.WriteUtf8(_afToken);
    protected override void RenderVolumeSlider(HtmxRenderContext ctx)     => _volume.Render(ctx.Next());
    protected override void RenderBassSlider(HtmxRenderContext ctx)       => _bass.Render(ctx.Next());
    protected override void RenderTrebleSlider(HtmxRenderContext ctx)     => _treble.Render(ctx.Next());
    protected override void RenderSaveBtn(HtmxRenderContext ctx)          => _save.Render(ctx.Next());
    protected override void RenderSuccessAlert(HtmxRenderContext ctx)     => _success.Render(ctx.Next());
}
```

**POST handler**
```csharp
[Handler]
[MapPost("/settings/audio")]
public static partial class PostAudioSettingsHandler
{
    public record Command(
        [property: FromForm] int Volume,
        [property: FromForm] int Bass,
        [property: FromForm] int Treble);

    private static Task<IResult> HandleAsync(
        [AsParameters] Command cmd, HttpContext ctx, IAntiforgery af, CancellationToken ct)
    {
        var prefs = new AudioPrefs(cmd.Volume, cmd.Bass, cmd.Treble);
        // Persist prefs…
        return ctx.WriteHtmxPage(
            new AudioSettingsPage(af, ctx, prefs, saved: true), title: "Audio settings");
    }
}

public record AudioPrefs(int Volume, int Bass, int Treble);
```

**`AppJsonSerializerContext.cs`**
```csharp
[JsonSerializable(typeof(PostAudioSettingsHandler.Command), TypeInfoPropertyName = "AudioSettingsCommand")]
```