Dart Drag and Drop

Drag and Drop for Dart web apps with mouse and touch support.

GitHub | Pub | Demos and Examples

Features

• Use any HTML Element as

  Draggable

  or

  Dropzone

  .
• Mouse and Touch dragging.
• Draggable events:

  dragStart

  ,

  drag

  , and

  dragEnd

• Dropzone events:

  dragEnter

  ,

  dragOver

  ,

  dragLeave

  , and

  drop

• Drag avatars as visual indication of a drag operation:
  • Original element as drag avatar.
  • Clone as drag avatar.
  • Custom drag avatar.
• Support for Shadow DOM (Web Components, Custom Elements, Polymer, etc.).
• Much more... see examples.

Usage

Before you read the instructions below, you should take a look at the examples.

Basic Set Up

Create a

Draggable

Element

ElementList

querySelectorAll

If you also want to drop somewhere, you'll need a

Dropzone

// Install draggable (no avatar).
Draggable draggable = Draggable(querySelectorAll('.draggable'));

// Install dropzone.
Dropzone dropzone = Dropzone(querySelector('.dropzone'));

You'll most likely want some drag avatar to show the user that a drag is going on. There are two predefined

AvatarHandler

AvatarHandler

// Draggable with clone as avatar.
Draggable draggable = Draggable(querySelectorAll('.draggable'),
    avatarHandler: AvatarHandler.clone());


// Draggable with original element as avatar.
Draggable draggable = Draggable(querySelectorAll('.draggable'),
    avatarHandler: AvatarHandler.original());

Draggable Options

The following options can be passed as named parameters to the constructor of

Draggable

• avatarHandler

  : Is responsible for creating, position, and removing a drag avatar. A drag avatar provides visual feedback during a drag operation. Here are possible options (see above for an example):

  • null

    (the default) - will not create a drag avatar

  • AvatarHandler.original()

    - handler that uses the original draggable as avatar. See

    OriginalAvatarHandler

    .

  • AvatarHandler.clone()

    - handler that uses a clone of the draggable element as avatar. See

    CloneAvatarHandler

    .
  • A custom

    AvatarHandler

    - you can provide your own implementation of

    AvatarHandler

    .

• horizontalOnly

  : If set to true, only horizontal dragging is tracked. This enables vertical touch dragging to be used for scrolling.

• verticalOnly

  : If set to true, only vertical dragging is tracked. This enables horizontal touch dragging to be used for scrolling.

• handle

  : If handle query String is specified, it restricts the dragging from starting unless it occurs on the specified element(s). Only elements that descend from the draggables elements are permitted.

• cancel

  : If cancel query String is specified, drag starting is prevented on specified elements.

• draggingClass

  : Is the css class set to the dragged element during a drag. If set to null, no such css class is added.

• draggingClassBody

  : Is the css class set to the html body tag during a drag. If set to null, no such css class is added.

• minDragStartDistance

  : Is the minimum distance in pixels that is needed for a drag to start. Default is

  4

  . This allows for clicks with tiny movement.

Draggable Events

Available event

Stream

Draggable

• onDragStart

  : Fired when the user starts dragging.
  Note:

  onDragStart

  is fired not on touchStart or mouseDown but as soon as there is a drag movement. When a drag is started an

  onDrag

  event will also be fired.

• onDrag

  : Fired periodically throughout the drag operation.

• onDragEnd

  : Fired when the user ends the dragging.
  Note: Is also fired when the user clicks the 'esc'-key or the window loses focus.

Dropzone Options

The following options can be passed as named parameters to the constructor of

Dropzone

• acceptor

  : Is used to determine which

  Draggable

  s will be accepted by this

  Dropzone

  . If none is specified, all

  Draggable

  s will be accepted.

• overClass

  : Is the css class set to the dropzone element when an accepted draggable is dragged over it. If set to null, no such css class is added.

• invalidClass

  : Is the css class set to the dropzone element when a not-accepted draggable is dragged over it. If set to null, no such css class is added.

Dropzone Events

Available event

Stream

Dropzone

• onDragEnter

  : Fired when a

  Draggable

  enters this

  Dropzone

  .

• onDragOver

  : Fired periodically while a

  Draggable

  is moved over a

  Dropzone

  .

• onDragLeave

  : Fired when a

  Draggable

  leaves this

  Dropzone

  .

• onDrop

  : Fired when a

  Draggable

  is dropped inside this

  Dropzone

  .

Note:

Dropzone

Draggable

Acceptor

Shadow DOM

Web Components create a nice ecapsulation through Shadow DOM. But this creates a problem with dropzones inside the Shadow DOM as they never receive events because all events are captured by the host element. To make this work we need to retarget events to the Shadow DOM children through recursive

elementFromPoint()

For performance reasons it wouldn't make sense to retarget all drag and drop events. If you wish to retarget events to the Shadow DOM children, you must add a

dnd-retarget

// Retarget drag and drop events to Shadow DOM children.

Attribution

The Dart Drag and Drop library is inspired by

• jQuery UI Draggable
• Draggabilly

Thank you for your work!

Running / Building / Testing

• Run from the terminal:

  webdev serve

• Build from the terminal:

  webdev build

License

The MIT License (MIT)