The Yoix^® Scripting Language

The type that is assigned to the event argument in the declaration of dragEnter selects the events that dragEnter receives. If event is declared to be a DropTargetEvent then DragSourceEvents will not arrive, if it is declared to be a DragSourceEvent then DropTargetEvents will not arrive, but if event is an Object then DropTargetEvents and DragSourceEvents can arrive and dragEnter should check event, usually using instanceof, to decide what to do.

In most situations dragEnter and drop are the only two event handlers a component will implement when it wants to accept data that is being transferred by a drag and drop operation. dragEnter receives DropTargetEvents when its declaration lets them through and the cursor enters the component. dragEnter usually examines fields, like dragowner, mimetypes, and transferable in its event argument and then returns a Number that is non-zero if it accepts and zero if it rejects the data that is being transferred by the drag and drop operation. A return value that is missing or the wrong type (e.g., a String) also means the data is rejected.

A much less important use of dragEnter is as an event handler that receives DragSourceEvents, which happens when its declaration lets them through and the cursor enters any component that accepts the data that this component's dragGestureRecognized exported. dragEnter may choose to change the cursor field in its event argument if a visual effect is called for, but in this case nothing special is required and any return value from dragEnter will be ignored.

Some Swing components provide automatic drag and drop handling that currently must be disabled by storing NULL in their transferhandler field before your drag and drop event handlers will start working. In other words, you probably should include a declaration that looks something like,

Object transferhandler = NULL;