dropCallback problem Maya2015

[haggi_master]

Hi,

I want to create a new window like this with drop functionality:

global proc callbackName(string $dragControl, string $dropControl, string $msgs[], int $x, int $y, int $type) 
{
    print("dropCallback");
}

window;
columnLayout -columnAttach "both" 5 -rowSpacing 20 -columnWidth 250 -dropCallback "callbackName" -dragCallback "dcallbackName";
button  -dropCallback "callbackName";
button  -dropCallback "callbackName";
showWindow;

My goal is to drag shader nodes from the hypershade window and drop it onto my window. But this procedure does not work, dropping is not enabled. What works is to drag and drop the buttons onto each other, but this is useless in this case. So my question is: Is it possible to create a new window and drag an drop shader nodes onto it?

I do not need necessarily a mel solution I'd be happy with python solution or python with pyside.