Swing Hacks

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Chapter 7, Text

#50 Auto-Completing Text Fields

HACK

You can hide the window at this point and look at the selection value. Since

the

Completer just puts Strings in the list model, you can pull out the

selected value and set that as the text of the field. And you’re done.

Well, not quite. If you call

setText( )

directly in

valueChanged( )

, you’ll be

thrown an

IllegalStateException

. The problem is that you’re attempting to

change the value of the

Document

while it’s already being changed. In other

words, firing off the

DocumentEvent is part of the document edit that began

with the user’s keystroke that led to the completion menu appearing; this

edit needs to complete before another is attempted. As you can see in this

hack, the workaround is to create a worker thread to set the field with the

clicked text, and to invoke that worker on a later cycle through the event

loop. This arrangement returns immediately and lets the first edit finish,

then sets the field later.

Test Out Auto-Complete

To test this class, you need to put the CompletableJTextField in a GUI and

provide a way to give it some completions. The

TestCompletableJTextField

class in Example 7-5 does just that, offering a second JTextField where you

can enter strings that will be offered as completions to text typed into the

CompletableJTextField. When run, the test GUI originally looks like

Figure 7-3.

Example 7-5. A GUI to exercise the CompletableJTextField ...