Swing Hacks

Debug Components with a Custom Glass Pane #96

Chapter 12, Miscellany

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481

HACK

from/subject of one email message, the details of a downloaded file, etc.). In

cases like these, I’ll try to see if a

JList with a multi-line cell renderer [Hack #16]

can keep all the data together in a visually pleasing form. So, when is hori-

zontal scrolling OK? I think it’s appropriate when the data you’re displaying

is not row-oriented, and instead you’re scrolling up, down, and across a

single cohesive thing, like a large image or, in this case, a stack trace.

H A C K

#96

Debug Components with a Custom Glass PaneHack #96

Show component boundaries at runtime using a glass pane.

Sometimes when I’m building a really complicated Swing layout, I start to

lose track of what I’m looking at. Which component is this? Does that panel

extend all the way to the end of the frame? A way to visualize the layout

would be a useful addition to the usual development tools. This hack

explores using a custom glass pane to highlight each component and its

classname.

A glass pane is a normally transparent Swing component that is drawn on

top of all of the other components in a frame, as you saw when you put

dialog-like “sheets” into the glass pane

[Hack #44]. It is this ability that forms

the center of the hack. The custom glass pane will traverse the entire tree of

components in the frame, filling a translucent rectangle over each compo-

nent. Deeper components will get painted multiple times resulting in a

darker color. The glass pane will also watch the mouse cursor to determine

which component the user is pointing at. That component’s classname will

then be drawn in the glass pane as well.

Figure 12-10. Capturing standard out and err to Swing windows