# Angular Dropdown Component

> Angular Dropdown component allows you to toggle contextual overlays for displaying lists, links, and more html elements.

## Overview
Dropdowns are toggleable, contextual overlays for displaying lists of links and more.

Dropdowns are built on a third party library, [Popper.js](https://popper.js.org/), which provides dynamic positioning
and viewport detection. Popper.js isn't used to position dropdowns in navbars though as dynamic positioning isn't
required.

## Accessibility

The [<abbr title="Web Accessibility Initiative">WAI</abbr> <abbr title="Accessible Rich Internet Applications">ARIA</abbr>](https://www.w3.org/TR/wai-aria/) standard defines an actual [`role="menu"` widget](https://www.w3.org/TR/wai-aria/#menu), but this is specific to application-like menus which trigger actions or functions. <abbr title="Accessible Rich Internet Applications">ARIA</abbr> menus can only contain menu items, checkbox menu items, radio button menu items, radio button groups, and sub-menus.

CoreUI for Angular's dropdowns, on the other hand, are designed to be generic and applicable to a variety of situations and markup structures. For instance, it is possible to create dropdowns that contain additional inputs and form controls, such as search fields or login forms. For this reason, CoreUI for Angular does not expect (nor automatically add) any of the `role` and `aria-` attributes required for true <abbr title="Accessible Rich Internet Applications">ARIA</abbr> menus. Authors will have to include these more specific attributes themselves.

However, CoreUI for Angular does add built-in support for most standard keyboard menu interactions:

- <kbd>Enter</kbd>, <kbd>Space</kbd> or a click on the toggle opens and closes the menu. <kbd>ArrowDown</kbd> opens it and moves focus to the first item, <kbd>ArrowUp</kbd> to the last one.
- <kbd>ArrowDown</kbd> and <kbd>ArrowUp</kbd> move between `cDropdownItem` elements and wrap at the ends; <kbd>Home</kbd> and <kbd>End</kbd> jump to the first and last item. <kbd>Tab</kbd> moves through the menu natively.
- <kbd>Esc</kbd> closes the menu and returns focus to the toggle, and <kbd>Tab</kbd> leaving the menu closes it; with `autoClose` set to `false` neither does.
- Keys other than <kbd>Esc</kbd> pressed inside an input other than a button, a select, a textarea or a contenteditable in the menu are left to that control.

An `a` element used as the toggle gets `role="button"`. Give it an `href` so it is focusable and reachable with <kbd>Tab</kbd>, and keep its content non-interactive: a button exposes its children as plain text.

## Examples
Bind the dropdown toggle and the dropdown menu inside `c-dropdown`, or different element that declares `position: relative;`. Dropdowns can be triggered from `a` or `button` elements to better fit your possible requirements.

### Single button
Here's how you can put them to work with either `button` elements:

And with `a` elements:

The best part is you can do this with any button variant, too:

### Split button

Similarly, create split button dropdowns with virtually the same markup as single button dropdowns, but with the
addition of boolean prop `split` for proper spacing around the dropdown caret.

We use this extra class to reduce the horizontal `padding` on either side of the caret by 25% and remove the
`margin-left` that's attached for normal button dropdowns. Those additional changes hold the caret centered in the
split button and implement a more properly sized hit area next to the main button.

### Sizing

Button dropdowns work with buttons of all sizes, including default and split dropdown buttons.

### Dark dropdowns
Opt into darker dropdowns to match a dark navbar or custom style by set `dark` property. No changes are required to the dropdown items.

And putting it to use in a navbar:

## Directions

> RTL  Directions are mirrored when using CoreUI in RTL, meaning `dropstart` will appear on the right side.

### Centered

Trigger dropdown menus centered below the toggle by adding `direction="center"` to the `c-dropdown` component.

### Dropup

Trigger dropdown menus above elements by adding `direction="dropup"` to the `c-dropdown` component.

### Dropup Centered

Trigger dropup menu centered above the toggle by adding `direction="dropup-center"` to the `c-dropdown`component.

### Dropright

Trigger dropdown menus at the right of the elements by adding `direction="dropend"` to the `c-dropdown`component.

### Dropleft

Trigger dropdown menus at the left of the elements by adding `direction="dropstart"` to the `c-dropdown`component.

## Menu items

Historically dropdown menu contents had to be links, but that's no longer the case with v4. Now you can optionally use `button` elements in your dropdowns instead of just `a`.

You can also create non-interactive dropdown items with `cDropdownItemText`.

### Active
Set boolean property `active` to style item as active.

### Disabled
Add `disabled` boolean property to items in the dropdown to style them as disabled.

## Menu alignment

By default, a dropdown menu is automatically positioned 100% from the top and along the left side of its parent, which is what `alignment="start"` sets explicitly. Add `alignment="end"` to right align the dropdown menu.

> Heads up! Dropdowns are positioned thanks to Popper.js.

### Responsive alignment

If you use responsive alignment, dynamic positioning is disabled — the classes place the menu themselves. Set `variant="btn-group"` so that the dropdown wraps just the toggle; with the default variant it is a full-width block, and the menu aligns to the edge of the container instead of the button.

To align **right** the dropdown menu with the given breakpoint or larger, bind `[alignment]="{ lg: 'end' }"`, replacing `lg` with any of `xs`, `sm`, `md`, `lg`, `xl`, `xxl`.

To align **left** the dropdown menu with the given breakpoint or larger, bind `[alignment]="{ xs: 'end', lg: 'start' }"`. Every entry of the map adds its own class, so this one is right aligned by default and left aligned from `lg` up.

## Menu content

### Headers

Add a header to label sections of actions in any dropdown menu.

In the following example we use div without `cDropdownMenu` to show dropdown menu content.

### Dividers

Separate groups of related menu items with a divider.

In the following example we use div without `cDropdownMenu` to show dropdown menu content.

### Text

Place any freeform text within a dropdown menu with text. Note that you'll likely need additional sizing styles to constrain the menu width.

### Forms

Put a form within a dropdown menu, or make it into a dropdown menu.

## API reference

### Dropdown Module

```typescript
import { DropdownModule } from '@coreui/angular';

@NgModule({
    imports: [DropdownModule,]
})
export class AppModule() { }
```

### c-dropdown
_component_

```jsx
import { DropdownComponent } from '@coreui/angular'
```

### Props

| Name | Type | Default | Description |
| --- | --- | --- | --- |
| `alignment` | `DropdownAlignment` | - | Set alignment of dropdown menu. |
| `autoClose` | `boolean \| 'inside' \| 'outside'` | `true` | Configure the auto close behavior: - `true` closes the dropdown on a click inside or outside the menu, - `false` only on the toggle button or an explicit hide/toggle call and not on the `Esc` key, - `inside` only on a click inside the menu, - `outside` only on a click outside it. |
| `dark` | `boolean` | `false` | Sets a darker color scheme. If the colorScheme is set to 'dark', the dark theme will be applied. |
| `direction` | `'center' \| 'dropup' \| 'dropup-center' \| 'dropend' \| 'dropstart'` | - | Sets a specified  direction and location of the dropdown menu. |
| `placement` | `Placement` | `'bottom-start'` | Describes the placement of your component after Popper.js has applied all the modifiers that may have flipped or altered the originally provided placement property. |
| `popper` | `boolean` | `true` | If you want to disable dynamic positioning set this property to `false`. |
| `popperOptions` | `Partial<Options>` | `{}` | Optional Popper.js options object; the `placement` prop takes precedence over the placement set here. See https://popper.js.org/docs/v2/constructors/#options |
| `variant` | `'btn-group' \| 'dropdown' \| 'input-group' \| 'nav-item'` | `'dropdown'` | Set the dropdown variant to a btn-group, dropdown, input-group, and nav-item. |
| `visible` | `boolean` | `false` | Toggle the visibility of dropdown menu component. |

### Events

| Name | Description |
| --- | --- |
| `visibleChange` | Event emitted on `visible` change. |

### cDropdownClose
_directive_

```jsx
import { DropdownCloseDirective } from '@coreui/angular'
```

### Props

| Name | Type | Default | Description |
| --- | --- | --- | --- |
| `disabled` | `boolean` | `false` | Disables a dropdown-close directive. |
| `dropdownComponent` | `DropdownComponent` | - | The dropdown component instance this cDropdownClose belongs to. |
| `tabIndex` | `string \| number \| null` | `null` | Tab index of the dropdown-close element. |

### cDropdownDivider
_directive_

```jsx
import { DropdownDividerDirective } from '@coreui/angular'
```

### cDropdownHeader
_directive_

```jsx
import { DropdownHeaderDirective } from '@coreui/angular'
```

### cDropdownItem
_directive_

```jsx
import { DropdownItemDirective } from '@coreui/angular'
```

### Props

| Name | Type | Default | Description |
| --- | --- | --- | --- |
| `active` | `boolean` | `undefined` | Set active state to a dropdown-item. |
| `autoClose` | `boolean` | `true` | Configure dropdown-item close dropdown behavior. |
| `disabled` | `boolean` | `false` | Disables a dropdown-item. |
| `role` | `string` | `undefined` | Role for dropdown-item. |
| `tabIndex` | `string \| number \| null` | `'0'` | Tab index of the dropdown-item. |

### cDropdownItemPlain
_directive_

```jsx
import { DropdownItemPlainDirective } from '@coreui/angular'
```

### cDropdownMenu
_directive_

```jsx
import { DropdownMenuDirective } from '@coreui/angular'
```

### Props

| Name | Type | Default | Description |
| --- | --- | --- | --- |
| `alignment` | `DropdownAlignment` | - | Set alignment of dropdown menu. |
| `dark` | `boolean` | `false` | Sets a darker color scheme. If the colorScheme is set to 'dark', the dark theme will be applied. |
| `visible` | `boolean` | `false` | Toggle the visibility of dropdown menu component. |

### cDropdownToggle
_directive_

```jsx
import { DropdownToggleDirective } from '@coreui/angular'
```

### Props

| Name | Type | Default | Description |
| --- | --- | --- | --- |
| `caret` | `boolean` | `true` | Enables pseudo-element caret on toggler. |
| `disabled` | `boolean` | `false` | Disables the toggler. |
| `dropdownComponent` | `DropdownComponent` | `undefined` | Reference to dropdown component. |
| `split` | `boolean` | `false` | Create split button dropdowns with virtually the same markup as single button dropdowns, but with the addition of `.dropdown-toggle-split` class for proper spacing around the dropdown caret. |