Swing Hacks

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Chapter 9, Drag-and-Drop

#69 Translucent Drag-and-Drop

HACK

The quality of the interaction is greatly enhanced by the quantity of informa-

tion provided by the visual feedback. Another example is dragging a link

from the web browser to the desktop, where a translucent text box contain-

ing the link title and the URL is shown. Wouldn’t it be great to be able to do

the same in your application? Thankfully, Swing is perfectly suited for that

kind of job.

Translucence Rocks

Implementing a stylish drag-and-drop requires being able to draw a translu-

cent picture over any component. Every Swing frame contains several layers

on which components are painted. These layers serve many purposes,

among which is the drawing of pop-up menus over the regular components.

The higher-level layer is called the glass pane. A glass pane is a transparent

container you can use to draw over the entire UI, as seen in the hack that

turned dialogs into frame-anchored “sheets”

[Hack #44]. You will use it to

display translucent pictures during a drag-and-drop operation, as seen in

Figure 9-9.

Yet, translucent pictures do not cover all the needs of effective drag-and-

drop visual feedback. When the user drops a file on your application, you

can use a picture to indicate what the type of the file is. However, what pic-

ture will you use when the user wants to drag a text box into another box,

and expect the contents of the first box to be copied to the second? The best

Figure 9-9. A translucent picture as visual feedback for drag-and-drop