This repository reproduces a problem with the Angular CDK drag-and-drop module.

I expected all three cards to have working drag-and-drop lists that allow the user to reorder the same underlying words list.

In fact, the middle one does not work, because it is generated by a *ngFor over the result of a method on the component. Trying to drag and drop words in this card simply does not do anything; there is no compile error, or any error or warning on the JavaScript console.

This was raised as the following issue in the angular/components project: angular/components#21682

There, it emerged that this is not in fact a drag-and-drop bug but a consequence of how Angular change detection works. As items are dragged in the middle card, change detection constantly fires, which causes the method to keep being re-evaluated. This destroys the item being dragged.

One solution I found (bottom card) was to use an Angular pipe. This works, provided the input array is not modified in place (pure pipes only trigger when their input values change from the point of view of referential equality).

This project was generated with Angular CLI version 11.1.1.

Run ng serve for a dev server. Navigate to http://localhost:4200/. The app will automatically reload if you change any of the source files.

Run ng generate component component-name to generate a new component. You can also use ng generate directive|pipe|service|class|guard|interface|enum|module.

Run ng build to build the project. The build artifacts will be stored in the dist/ directory. Use the --prod flag for a production build.

Run ng test to execute the unit tests via Karma.

Run ng e2e to execute the end-to-end tests via Protractor.

To get more help on the Angular CLI use ng help or go check out the Angular CLI Overview and Command Reference page.