cdk drag: add ability to update internal _activeTransform

[fxck]

I want to use cdkDrag for the dragging part of a custom scrollbar. But the thing is, the native scroll occurs, I apply transform3d to the custom scrollbar thumb, which is simultaneously the drag handle, now when I try to drag after scroll occurred, those transforms get all messed up.

So ideally I would like to be able to sync those values.

This works:

(this.cdkDragYRef as any)._dragRef._activeTransform.y = this._scrollbarPosition.y;
(this.cdkDragXRef as any)._dragRef._activeTransform.x = this._scrollbarPosition.x;

[crisbeto]

That was one of the purposes of the cdkDragFreeDragPosition input, although I'm not completely sure how well it'll work if it's being updated while dragging.

[fxck]

Looks like updating _activeTransform like this doesn't quite work either.

[fxck]

Is there a way to update cdkDragFreeDragPosition with method? I'm trying not to trigger change detection..

Edit: this looks like it's working, gonna test it some more

    if (this._scrollbarSize.y) {
      this.trackYRef.nativeElement.style.transform = `translate3d(0, ${this._scrollbarPosition.y}px, 0)`;
      this.cdkDragYRef._dragRef.setFreeDragPosition({ y: this._scrollbarPosition.y, x: 0 });
      // (this.cdkDragYRef as any)._dragRef._activeTransform.y = this._scrollbarPosition.y;
    }

    if (this._scrollbarSize.x) {
      this.trackXRef.nativeElement.style.transform = `translate3d(${this._scrollbarPosition.x}px, 0, 0)`;
      this.cdkDragXRef._dragRef.setFreeDragPosition({ x: this._scrollbarPosition.x, y: 0 });
      // (this.cdkDragXRef as any)._dragRef._activeTransform.x = this._scrollbarPosition.x;
    }

[fxck]

I'm closing this @crisbeto, cdkDragFreeDragPosition does exactly what I want. And _dragRef.setFreeDragPosition works, albeit it's going thru that private property.

I'd suggest naming cdkDragFreeDragPosition something more descriptive and adding a setFreeDragPosition method to CdkDrag.

What do you think, should I make a PR (for that method at least, that rename would probably be breaking change not work doing right now I guess..)?

[crisbeto]

I agree that the name isn't great, but I couldn't come up with anything more descriptive.

Regarding the method, won't it be a little redundant? The input basically calls directly into it.

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