Roundbutton Class Code Tour - Motorola T720 Developer's Manual

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Figure 20.

Observe how the screen has automatically scrolled to fully display the second button. This

vertical scrolling is a feature provided by the LWT. If you press the down arrow on the

navigation button again, the focus jumps back to the topmost button on the screen. The

screen also scrolls back up to the top, so that you're looking at a screen that resembles

Figure 17. Try using both the up and down arrows to move the focus ownership among

the various buttons.

NOTE: The LWT reserves the vertical scrollbar to maneuver through the visible screen

components. You use horizontal scrollbars to implement sliders. However, you can extend

the LWT's components to process up, down, left, and right key events. You would do this

to implement a game or a special-purpose vertical market application.

Press the Exit soft key to quit the MIDlet and terminate the debugger session.

RoundButton Class Code Tour

Now that you understand how LWT components handle focus ownership and provide

desktop-quality visual feedback in response to events, let's take a tour of the code that

makes use of the Button class to implement the RoundButton class. The RoundButton

code shows you how easy it is to extend an LWT component. Start by double-clicking on

the file Buttons.java in the Project window to open the file in the editor.

import java.io.*;

import javax.microedition.midlet.*;

import javax.microedition.lcdui.*;

import com.motorola.lwt.*;

// The RoundButton class. Draws a round LWT button.

// Inherits the rest of its capabilities (such as

// key events) from the Button class.

The second round button has focus ownership. Note that the screen has

scrolled.

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