Installation

yarn add @angular-skyhook/core react-dnd-html5-backend

You might consider @angular-skyhook/multi-backend instead of the HTML5 backend, because it allows adding touch support as well.

Then import SkyhookDndModule and provide the backend:

import { SkyhookDndModule } from "@angular-skyhook/core";
import { default as HTML5Backend } from 'react-dnd-html5-backend'

@NgModule({
  imports: [
    // Don't forget the forRoot()
    SkyhookDndModule.forRoot({ backend: HTML5Backend }),
  ]
})
export class AppModule {}

If you need it again on a child module, like a lazy-loaded module, you only need to import SkyhookDndModule there. That way the backend and global drag state is only initialized once. But you may use forRootto inject a new instance or to include drag and drop on only some child modules.

When installing backends originally made for React (they all use default exports), make sure you use this syntax:

import { default as XXX } from '...'

... because Angular in AOT mode cannot do import XXX from '...' directly.

Concepts

These pieces make up the library:

1. An item (JS Object, not a DOM node) is the source of truth for each drag operation
2. A drag source registers a DOM node to commence drag operations
3. A drop target registers a DOM node for hover and drop events while dragging
4. A way for each to provide, listen for and query changes in the drag state: a monitor and appropriate callbacks
5. Hooks to provide some other DOM element as the drag preview.

react-dnd defined one more thing, inspired by HTML5, to make using this sane: each item has a type, and drag sources and drop targets will respectively emit and accept only items with matching types.

That's it. This library offers all those concepts in an Angular-friendly way, that is also largely compatible with a lot of react-dnd code and examples.

Next steps

• Have a look at the Examples, and browse their source code in the examples app on GitHub.

• Read and follow the Tutorial

• Read the 3-part guide in the sidebar. Any specifics are available by browsing the interfaces and classes.

Touch support and alternate backends

Mobile devices have not implemented HTML5 drag and drop. You will need:

• A different backend using click or touch events, without dropping desktop support
• A way to render drag previews. Where on desktops you can let the browser render drag previews, when using a backend based on click or touch events, on mobile you have to render them yourself.

A good way to solve both problems at once is using @angular-skyhook/multi-backend. It is based on the original dnd-multi-backend, which was designed to seamlessly switch between an HTML5 and a touch backend when it noticed different kinds of interaction. The @angular-skyhook version includes a preview component.

Note also that you will need to use an exported function to provide the backend, to retain AOT compatibility, if it requires assembly. MultiBackend, for example, can be used like so:

export function createBackend() {
    return MultiBackend(HTML5ToTouch);
}
@NgModule({
  imports: [
    SkyhookDndModule.forRoot({ backendFactory: createBackend })
  ]
}
// ...

Troubleshooting

I get TypeError: backend is null, only when AOT is enabled

Also rears its head as No such property 'default' of undefined.

Troubleshooting steps

1. Check you are importing the backend and renaming any default exports.

   import { default as HTML5Backend } from 'react-dnd-html5-backend';
   import { SomeImaginaryBackendWithNamedExports } from 'some-imaginary-backend';

   Generally, make sure you are importing the backend correctly. If it does not provide Typescript definitions, you might have to read the documentation or browse the source code.

2. Make sure in your root Angular module (usually app.module.ts) you import SkyhookDndModule.forRoot({ backend: MyBackend }) instead of plain SkyhookDndModule.

I get Error encountered resolving symbol values statically. Calling function 'default' with AOT enabled.

Make sure you are following the special instructions for assembly-required backends like MultiBackend or any backend that allows SomeBackend({ optionsHere: true }), like TouchBackend. See above.

In the spec callbacks, my component doesn't have any properties, and it can't call this.method()!

Make sure you use the arrow function syntax (() =>) in your specs so this will refer to your component. Example:

paperCount = 3;
limitedSupplyOfPaper = this.dnd.dragSource("PAPER", {
    // use shorthand for one-liners that return a value
    canDrag: () => this.paperCount > 0,
    endDrag: (monitor) => {
        if (monitor.didDrop()) {
            this.paperCount--;
        }
    }
});

This demo shows comprehensively what this refers to in arrow functions vs regular ones. A sufficiently advanced editor shouldn't show any completions at this.| in a regular function, as it will resolve the type of this to be any.