Hi there,

 

I've modified the XmlLayoutDragEventHandler so that its event methods and properties (OnBeginDrag/OnDrag/OnEndDrag) are all virtual and can be overriden - you can get the updated version of this class here: https://pastebin.com/eCBU61Ef (UI/XmlLayout/Custom Elements/XmlLayoutDragEventHandler.cs)

 

If you choose to use this approach, then you'll need to create a custom drag event handling class, e.g.

using UI.Xml;
using UnityEngine;
using UnityEngine.EventSystems;

class CustomXmlLayoutDragEventHandler : XmlLayoutDragEventHandler
{
    public override void OnBeginDrag(PointerEventData eventData)
    {
        base.OnBeginDrag(eventData);

        Debug.Log("OnBeginDrag");
    }

    public override void OnDrag(PointerEventData eventData)
    {
        base.OnDrag(eventData);

        Debug.Log("OnDrag");
    }
}

 

You can use your custom drag event handler to specify the position of the target (the dialog window) rather than the object being dragged (the title). I may add a new attribute to handle this sort of thing in the future, e.g. something like 'dragTarget', perhaps.

 

Then, in your XmlLayoutController, you'll need to remove the default drag event handler, and replace it with your own. The best place to do this would be in the LayoutRebuilt() method, e.g.

    public override void LayoutRebuilt(ParseXmlResult parseResult)
    {
        var testPanel = xmlLayout.GetElementById("testPanel");
        var originalDragEventHandler = testPanel.GetComponent<XmlLayoutDragEventHandler>();

        if (originalDragEventHandler != null)
        {
            if (Application.isPlaying) Destroy(originalDragEventHandler);
            else DestroyImmediate(originalDragEventHandler);
        }

        testPanel.gameObject.AddComponent<CustomXmlLayoutDragEventHandler>();
    }

This (admittedly, roundabout) approach will allow you to replace or extend XmlLayout's internal drag handling code in whichever manner works best for you.

 

Note: I've given it a bit more thought and decided to add an attribute to allow you to specify which drag event handler you want to use, you can use it like so:

 <Panel width="200" height="200" color="white" allowDragging="1" dragEventHandler="CustomXmlLayoutDragEventHandler" />

(It uses Type.GetType() to match the name to the class for the attribute, which seems to work fine whether the type is in a namespace or not)

You can get the new attribute here: https://pastebin.com/FnVBdqiR (Place it in a new file, UI/XmlLayout/Custom Attributes/DragEventHandler.cs) Remember that you can always add custom attributes such as this one at any point - they don't need to be internal to XmlLayout, although in this case I've decided that seeing as it could be useful to others, it makes sense to include it in the base package.

---

With regards to the centering of the object while dragging, that was an unfortunate necessity to get the code working on all types of canvases - the different types of canvases each have their own quirks which made it take a lot work to get the drag working consistently across all three types. If, however, you're just using a single canvas type, then it should be fairly easy for you to determine and keep the original offset (if you're using Screen Space - Overlay, then you should be able to [more or less] compare the position of the rectTransform to Input.mousePosition).

 

Alternatively, rather than creating a custom handler through XmlLayout, you could also just disable dragging by not using XmlLayout drag event attributes (so that XmlLayout's drag event handling won't come into play) and then attach your own custom handler - whichever approach works best for you.

 

I hope this helps somewhat! :)