Angular: Drag and Drop - Fill [cdkDropListConnectedTo] dynamically

Question

Drag and drop should be possible as follows.

• You can move items from container 1 to containers 2, 3 or 4.
• You are not allowed to move items from container 2, 3 or 4 to container 1.
• items from containers 2 to 4 can be moved back and forth.

I'm just missing [cdkDropListConnectedTo]

How do i have to populate [cdkDropListConnectedTo] to meet my needs?

Redundant code should be avoided as much as possible.

This is my current code.

<div *ngFor="let book of this.books; let i = index">
    <div>
        <div
            cdkDropList
            id="book-container-{{i}}"
            #ref{{i}}="cdkDropList"
            [cdkDropListData]="book.getDropListData()"
            [cdkDropListConnectedTo]= "[]"
            (cdkDropListDropped)="drop($event)">
            <div>
                <p class="headline">{{book.getHeadline()}}</p>
            </div>
        </div>
    </div>
</div>

Answer 1

Here is a example. You can move from container one to container two. But not back from two to one.

Here is the solution for the html part:

Use the cdkDropListEnterPredicateattribute. This fires if any item over the other container. Here is the documentation.

<div
  cdkDropList
  id="two"
  [cdkDropListData]="basket"
  class="example-list"
  (cdkDropListDropped)="drop($event)"
  [cdkDropListEnterPredicate]="canDrop">
      <div class="example-box" *ngFor="let item of basket" cdkDrag>{{item}}</div>
</div>

The code behind:

Here we check the id of the item.dropContainer (the start container it was nested) and the list.id (the target container you wanna drop). Simple if you move from two -> one return false.

  canDrop(item: CdkDrag, list: CdkDropList) {
    console.log(item.dropContainer.id, list.id);

    if (item.dropContainer.id === 'two' && list.id === 'one') return false;
    return true;
  }

Try it all here in Stackblitz!