Support cancellation of movement

[bbc]

Support cancellation of movement

[thomascgray]

Thanks for raising the issue @do0g , and for the chat earlier!

To continue from what Jordan said, some initial thoughts...

During the actual process of handling a movement, before the assignFocus() is called (thus "completing the movement") we provide an opportunity for a callback to fire.

If said callback returns true, instead of assigning the focus and firing the focus and move events, we fire a cancelled event on the instance itself e.g

navigation.on('cancelled', (leaveNode, enterNode) => {
  // leaving `leaveNode` and entering `enterNode` was cancelled for reasons...
});

(We can also, at that point, call an onCancelled hook if one was supplied on the node to be focused.)

navigation.registerNode('myBox', {
  parent: 'myContainer',
  onCancelled: (leave, enter) => {
    // movement from `leave` to `enter` was cancelled, where `enter` is _this_ node itself
  }
}

The actual cancellation callback itself should also live against the node that was to be "entered", I'm thinking? Some kind of shouldCancel() callback.

navigation.registerNode('myBox', {
  parent: 'myContainer',
  onCancelled: (leave, enter) => {
    // movement from `leave` to `enter` was cancelled, where `enter` is _this_ node itself
  },
  shouldCancel: (leave, enter) : boolean => {
    // movement from `leave` to `enter` is happening, here is an opportunity
    // to call some business logic to `return false` and stop that movement
  }
}

Otherwise, perhaps a shouldCancel() on the instance itself? And it is called for every movement that happens. Before both in fact.

navigation
  .registerNode('root')
  .registerNode('box1')
  .registerNode('box2')
  .registerNode('box3')

navigation.shouldCancel((leave, enter => {
  // movement from `leave` to `enter` is happening, here is an opportunity
  // to call some business logic to `return true` and stop that movement
})

[jordanholt]

Interesting use case... I think I would prefer the first described implementation where the move operation provides a callback, and if that callback returns true, the move completes.

[jordanholt]

Another point worth thinking about is how this interacts (if at all) with the existing "overrides" mechanism.

[do0g]

This looks pretty good to me. Either of the node or instance solutions would probably work for us, but both would be very flexible.

[thomascgray]

Closing this issue, as it was fixed by #30