ConcurrentModificationException when updating a DragAndDropCellList

[Romain Kolb]

Hello,

I'm using the DND bundle (v1.0.5) to manage drag'n'dropping between different CellLists. The CellLists represent a hierarchy of folders with root folders, sub folders and files :

Root folder 1
|-->Sub folder 1
|     |--> File 1
|     |--> File 2
|--> Sub folder 2
Root folder 2
|--> Sub folder 3
|...

I've got 2 PopupWidgets (each containing a DragAndDropCellList), one for the subfolders list and one for the files list. When I hover over a root folder, the subfolder PopupWidget's CellList is updated with the subfolders of the root folder, and the PopupWidget is shown next to the root folder.

My goal is to be able to move files and subfolders by drag'n'dropping them around. I started from the CellList example and it's working rather well, but I'm encountering an issue when moving subfolders :
- Hover Root folder 1 => subfolder PopupWidget updates its CellList with the subfolders of root folder 1, opens next to root folder 1
- Drag a sub folder to the root folders CellList
- Still dragging, hover root folder 2

What I expect to happen :
- subfolder PopupWidget closes, updates its CellList with the subfolders of root folder 2, then opens next to root folder 2
- I can continue dragging the subfolder to the subfolder PopupWidget

Instead I get the following exception, and the dragged subfolder gets stucked :

java.util.ConcurrentModificationException: null
    at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
    at java.util.AbstractList$Itr.next(AbstractList.java:343)
    at gwtquery.plugins.droppable.client.DragAndDropManagerImpl.drag(DragAndDropManagerImpl.java:85)
    at gwtquery.plugins.draggable.client.Draggable.mouseDragImpl(Draggable.java:464)
    at gwtquery.plugins.draggable.client.Draggable.mouseDrag(Draggable.java:287)
    at com.google.gwt.query.client.plugins.MousePlugin.mouseMove(MousePlugin.java:164)
    at com.google.gwt.query.client.plugins.MousePlugin$3.f(MousePlugin.java:217)
    at com.google.gwt.query.client.Function.f(Function.java:178)

My guess is that the CellList is updating while gquery does its magic, any idea how I could correct or work around the issue ?

Thanks in advance,

Romain

[Julien Dramaix]

I guess your subfolders in the CellList are also drop targets ?

The problem is that you are modifying the list of drop targets during
a drag operation.
Try to call :
DragAndDropManager.getInstance().update(ctx);
just after you modify the list of subfolder (when the mouse hovers
another root folder)

Let's me know if it works,

Julien

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[Romain Kolb]

Hello,

In dnd-bundle 1.0.5, DragAndDropManager doesn't have an update(DragContext ctx) method, only update() (which doesn't seem to fix my problem).
I found it in the trunk of the Droppable Plugin however. Should I build and use the head version of the bundle ? Is it stable enough to be used in production ?
Another question : how should I get a reference to the DragContext when calling update(ctx) ?

Thanks a lot for this project and quick support, I really appreciate it.

[Julien Dramaix]

> Should I build and
> use the head version of the bundle ? Is it stable enough to be used in
> production ?

Nope, the trunk is in development and I can't promise that the code is stable...

> Another question : how should I get a reference to the DragContext
> when calling update(ctx) ?

the DragContext is passed as parameters in all event handlers.

I apologize for the delay of my reply

Julien

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