The @angular/cdk/drag-drop module provides you with a way to easily and declaratively create
drag-and-drop interfaces, with support for free dragging, sorting within a list, transferring items
between lists, animations, touch devices, custom drag handles, previews, and placeholders,
in addition to horizontal lists and locking along an axis.
Start by importing DragDropModule into the NgModule where you want to use drag-and-drop
features. You can now add the cdkDrag directive to elements to make them draggable. When
outside of a cdkDropList element, draggable elements can be freely moved around the page.
You can add cdkDropList elements to constrain where elements may be dropped.
Adding cdkDropList around a set of cdkDrag elements groups the draggables into a
reorderable collection. Items will automatically rearrange as an element moves. Note
that this will not update your data model; you can listen to the cdkDropListDropped event to
update the data model once the user finishes dragging.
The cdkDropList directive supports transferring dragged items between connected drop zones.
You can connect one or more cdkDropList instances together by setting the cdkDropListConnectedTo
property or by wrapping the elements in an element with the cdkDropListGroup attribute.
Note that cdkDropListConnectedTo works both with a direct reference to another cdkDropList, or
by referencing the id of another drop container:
<!-- This is valid -->
<div cdkDropList #listOne="cdkDropList" [cdkDropListConnectedTo]="[listTwo]"></div>
<div cdkDropList #listTwo="cdkDropList" [cdkDropListConnectedTo]="[listOne]"></div>
<!-- This is valid as well -->
<div cdkDropList id="list-one" [cdkDropListConnectedTo]="['list-two']"></div>
<div cdkDropList id="list-two" [cdkDropListConnectedTo]="['list-one']"></div>If you have an unknown number of connected drop lists, you can use the cdkDropListGroup directive
to set up the connection automatically. Note that any new cdkDropList that is added under a group
will be connected to all other lists automatically.
<div cdkDropListGroup>
  <!-- All lists in here will be connected. -->
  <div cdkDropList *ngFor="let list of lists"></div>
</div>You can associate some arbitrary data with both cdkDrag and cdkDropList by setting cdkDragData
or cdkDropListData, respectively. Events fired from both directives include this data, allowing
you to easily identify the origin of the drag or drop interaction.
<div cdkDropList [cdkDropListData]="list" *ngFor="let list of lists" (cdkDropListDropped)="drop($event)">
  <div cdkDrag [cdkDragData]="item" *ngFor="let item of list"></div>
</div>The cdkDrag and cdkDropList directive include only those styles strictly necessary for
functionality. The application can then customize the elements by styling CSS classes added
by the directives:
| Selector | Description | 
|---|---|
| .cdk-drop-list | Corresponds to the cdkDropListcontainer. | 
| .cdk-drag | Corresponds to a cdkDraginstance. | 
| .cdk-drag-disabled | Class that is added to a disabled cdkDrag. | 
| .cdk-drag-handle | Class that is added to the host element of the cdkDragHandle directive. | 
| .cdk-drag-preview | This is the element that will be rendered next to the user's cursor as they're dragging an item in a sortable list. By default the element looks exactly like the element that is being dragged. | 
| .cdk-drag-placeholder | This is element that will be shown instead of the real element as it's being dragged inside a cdkDropList. By default this will look exactly like the element that is being sorted. | 
| .cdk-drop-list-dragging | A class that is added to cdkDropListwhile the user is dragging an item. | 
| .cdk-drop-list-disabled | A class that is added to cdkDropListwhen it is disabled. | 
| .cdk-drop-list-receiving | A class that is added to cdkDropListwhen it can receive an item that is being dragged inside a connected drop list. | 
The drag-and-drop module supports animations both while sorting an element inside a list, as well as
animating it from the position that the user dropped it to its final place in the list. To set up
your animations, you have to define a transition that targets the transform property. The
following classes can be used for animations:
.cdk-drag - If you add a transition to this class, it'll animate as the user is sorting
  through a list..cdk-drag-animating - This class is added to a cdkDrag when the user has stopped dragging.
  If you add a transition to it, the CDK will animate the element from its drop position to
  the final position inside the cdkDropList container.Example animations:
/* Animate items as they're being sorted. */
.cdk-drop-list-dragging .cdk-drag {
  transition: transform 250ms cubic-bezier(0, 0, 0.2, 1);
}
/* Animate an item that has been dropped. */
.cdk-drag-animating {
  transition: transform 300ms cubic-bezier(0, 0, 0.2, 1);
}By default, the user can drag the entire cdkDrag element to move it around. If you want to
restrict the user to only be able to do so using a handle element, you can do it by adding the
cdkDragHandle directive to an element inside of cdkDrag. Note that you can have as many
cdkDragHandle elements as you want:
When a cdkDrag element is picked up, it will create a preview element visible while dragging.
By default, this will be a clone of the original element positioned next to the user's cursor.
This preview can be customized, though, by providing a custom template via *cdkDragPreview.
Note that the cloned element will remove its id attribute in order to avoid having multiple
elements with the same id on the page. This will cause any CSS that targets that id not
to be applied.
While a cdkDrag element is being dragged, the CDK will create a placeholder element that will
show where it will be placed when it's dropped. By default the placeholder is a clone of the element
that is being dragged, however you can replace it with a custom one using the *cdkDragPlaceholder
directive:
The cdkDropList directive assumes that lists are vertical by default. This can be
changed by setting the orientation property to `"horizontal".
If you want to stop the user from being able to drag a cdkDrag element outside of another element,
you can pass a CSS selector to the cdkDragBoundary attribute. The attribute works by accepting a
selector and looking up the DOM until it finds an element that matches it. If a match is found,
it'll be used as the boundary outside of which the element can't be dragged. cdkDragBoundary can
also be used when cdkDrag is placed inside a cdkDropList.
By default, cdkDrag allows free movement in all directions. To restrict dragging to a
specific axis, you can set cdkDragLockAxis on cdkDrag or cdkDropListLockAxis on cdkDropList
to either "x" or "y".
If there's an element that you want to make draggable, but you don't have direct access to it, you
can use the cdkDragRootElement attribute. The attribute works by accepting a selector and looking
up the DOM until it finds an element that matches the selector. If an element is found, it'll become
the element that is moved as the user is dragging. This is useful for cases like making a dialog
draggable.
By default, all cdkDrag items from one container can be moved into another connected container.
If you want more fine-grained control over which items can be dropped, you can use the
cdkDropListEnterPredicate which will be called whenever an item is about to enter a
new container. Depending on whether the predicate returns true or false, the item may or may not
be allowed into the new container.
If you want to disable dragging for a particular drag item, you can do so by setting the
cdkDragDisabled input on a cdkDrag item. Furthermore, you can disable an entire list
using the cdkDropListDisabled input on a cdkDropList or a particular handle via
cdkDragHandleDisabled on cdkDragHandle.
There are cases where draggable items can be dragged out of one list into another, however
the user shouldn't be able to sort them within the source list. For these cases you can set the
cdkDropListSortingDisabled input which will prevent the items in a cdkDropList from sorting,
in addition to preserving the dragged item's initial position in the source list, if the user
decides to return the item.
By default as soon as the user puts their pointer down on a cdkDrag, the dragging sequence will
be started. This might not be desirable in cases like fullscreen draggable elements on touch
devices where the user might accidentally trigger a drag as they're scrolling the page. For
cases like these you can delay the dragging sequence using the cdkDragStartDelay input which
will wait for the user to hold down their pointer for the specified number of milliseconds before
moving the element.
By default, standalone cdkDrag elements move from their normal DOM position only when manually
moved by a user. The element's position can be explicitly set, however, via the
cdkDragFreeDragPosition input. Applications commonly use this, for example, to restore a
draggable's position after a user has navigated away and then returned.