Once we have made our objects draggable we are ready to make them droppable. First, we need to define a valid drop zone, any zone that is not the valid one must return the selected object to its original state. Let's add some code to our objects so when it is not dropped in a valid zone it returns to its original state. To accomplish this, the
Ext.dd.DD class has some abstract methods that can be overridden:
startDrag: It is an abstract method that is called after a drag/drop object is clicked and the drag or mouse-down time thresholds have been met
onDrag: It is an abstract method that is called during the
onMouseMoveevent while dragging an object
onDragEnter: It is an abstract method that is called when this element begins ...