The overlay package provides a way to open floating panels on the screen.
The CDK overlays depend on a small set of structural styles to work correctly. If you're using Angular Material, these styles have been included together with the theme, otherwise if you're using the CDK on its own, you'll have to include the styles yourself. You can do so by importing the prebuilt styles in your global stylesheet:
@import '~@angular/cdk/overlay-prebuilt.css';
Calling overlay.create() will return an OverlayRef instance. This instance is a handle for managing that specific overlay.
The OverlayRef _is_ a PortalOutlet- once created, content can be added by attaching a Portal. See the documentation on portals for further information.
const overlayRef = overlay.create();
const userProfilePortal = new ComponentPortal(UserProfile);
overlayRef.attach(userProfilePortal);
When creating an overlay, an optional configuration object can be provided.
const overlayRef = overlay.create({
height: '400px',
width: '600px',
});
The full set of configuration options can be found in the API documentation.
The positionStrategy configuration option determines how the overlay will be positioned on-screen. There are two position strategies available as part of the library: GlobalPositionStrategy and ConnectedPositionStrategy.
GlobalPositionStrategy is used for overlays that require a specific position in the viewport, unrelated to other elements. This is commonly used for modal dialogs and application-level notifications.
ConnectedPositionStrategy is used for overlays that are positioned relative to some other "origin" element on the page. This is commonly used for menus, pickers, and tooltips. When using the connected strategy, a set of preferred positions is provided; the "best" position will be selected based on how well the overlay would fit within the viewport.
FlexibleConnectedPositionStrategy expands upon the functionality from the ConnectedPositionStrategy by adding more advanced features on top of being able to position an overlay relative to another element on the page. These features include the ability to have an overlay become scrollable once its content reaches the viewport edge, being able to configure a margin between the overlay and the viewport edge, having an overlay be pushed into the viewport if it doesn't fit into any of its preferred positions, as well as configuring whether the overlay's size can grow while the overlay is open. The flexible position strategy also allows for the transform-origin of an element, inside the overlay, to be set based on the current position using the withTransformOriginOn. This is useful when animating an overlay in and having the animation originate from the point at which it connects with the origin.
A custom position strategy can be created by implementing the PositionStrategy interface. Each PositionStrategy defines an apply method that is called whenever the overlay's position should be updated. A custom position strategy can additionally expose any other APIs necessary as related to the positioning of the overlay element.
The scrollStrategy configuration option determines how the overlay will react to scrolling outside the overlay element. There are four scroll strategies available as part of the library.
NoopScrollStrategy is the default option. This strategy does nothing.
CloseScrollStrategy will automatically close the overlay when scrolling occurs.
BlockScrollStrategy will block page scrolling while the overlay is open. Note that some applications may implement special or customized page scrolling; if the BlockScrollStrategy conflicts with this kind of situation, it can be overriden by re-providing BlockScrollStrategy with a custom implementation.
RepositionScrollStrategy will re-position the overlay element on scroll. Note that this will have some performance impact on scrolling- users should weigh this cost in the context of each specific application.
A custom scroll strategy can be created by implementing the ScrollStrategy interface. Each strategy will typically inject ScrollDispatcher (from @angular/cdk/scrolling) to be notified of when scrolling takes place. See the documentation for ScrollDispatcher for more information on how scroll events are detected and dispatched.
The OverlayContainer provides a handle to the container element in which all individual overlay elements are rendered. By default, the overlay container is appended directly to the document body so that an overlay is never clipped by an overflow: hidden parent.
The FullscreenOverlayContainer is an alternative to OverlayContainer that supports correct displaying of overlay elements in fullscreen mode.
FullscreenOverlayContainer can be enabled by providing it in your NgModule:
@NgModule({
providers: [{provide: OverlayContainer, useClass: FullscreenOverlayContainer}],
// ...
})
export class MyModule { }