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Building Easy Java GUIs with Thinlet, Part 2
by Keld H. Hansen
Part 1 of this series presented the architecture of a Thinlet application: a Java program and an XML configuration file defining the GUI—that's how simple it is. Part 2 explores some of Thinlet's more advanced features—like menus, dialogs, tabbed panes, and trees.
Using Menus
No GUI gets built without a menu bar, and Thinlet offers menu support for even rather complex menus. To show you how to build a menu, this articles starts by building a small application that can read a file and display the contents in a text area. You'll need a simple menu bar (shown in Figure 1).
To create this menu, you need a configuration file:
<panel columns="1" gap="4" top="4" left="4" bottom="4" right="4">
<menubar colspan="3" weightx="1">
<menu text="File">
<menuitem text="Open..." action="open()" />
<menuitem text="Save As..." action="save()" />
<separator/>
<menuitem text="Clear" action="clear(area)" />
</menu>
</menubar>
<textarea name="area" columns="25" rows="8"/>
</panel>
The "..." after Open and Save As indicates opening a dialog (this is implemented later in the article). You may add accelerators and short cut keys like in Figure 2.
Alt+F displays the File menu choices; Ctrl+C will clear the text area. The config file has this format:
<menu text="File" mnemonic="0">
<menuitem text="Open..." action="open()" />
<menuitem text="Save As..." action="save()" />
<separator/>
<menuitem text="Clear" action="clear(area)" accelerator="Ctrl C"/>
</menu>
Mnemonic="0" means that the first character in the word File is underlined and will work as shortcut key.
Menus can be very complex. Figure 3 is an example, taken from Thinlet's Showcase (select the "Widgets" item).
If the body of the GUI will scroll, then you might not want the menu bar to take part in the scrolling. To avoid this, set the scrollable property on a panel inside the main panel. Here's the config file:
<panel columns="1" gap="4" top="4" left="4" bottom="4" right="4">
<menubar colspan="3" weightx="1">
. . .
</menubar>
<panel scrollable="true" weightx="1" weighty="1">
<textarea name="area" columns="70" rows="20"/>
</panel>
</panel>
Remember to set weightx and weighty or you won't get scrollbars (Figure 4).
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