MIDP Programming - Java 2 Micro Edition Application Development - page 39

Tab l e 3.2. ImageItem Layout Constants
Constant Value
LAYOUT_CENTER The image is centered horizontally.
LAYOUT_DEFAULT A device-dependent default formatting is applied to the image.
LAYOUT_LEFT The image is left-aligned.
LAYOUT_NEWLINE_AFTER A new line will be started after the image is drawn.
LAYOUT_NEWLINE_BEFORE A new line will be started before the image is drawn.
LAYOUT_RIGHT

The image is aligned to the right.

The following code snippet shows how a center aligned ImageItem is added to the HelloMidp
sample MIDlet:

public HelloMidp() {
display = Display.getDisplay (this);
mainForm = new Form ("HelloMidp");
try {
ImageItem logo = new ImageItem
("Copyright: ", Image.createImage ("/mcp.png"),
ImageItem.LAYOUT_CENTER | mageItem.LAYOUT_NEWLINE_BEFORE
| ImageItem.LAYOUT_NEWLINE_AFTER, "Macmillian USA");

mainForm.append (logo);
} catch (IOException e) {
mainForm.append (new StringItem ("Copyright", "Sams
Publishing; Image not available:" + e));
}
}

By forcing a new line before and after the image, you ensure that the image is centered in its own line.
Figure 3.3 shows the corresponding display on the device. If the image cannot be loaded and an
exception is thrown, a simple StringItem is appended to the form instead of the image.

Figure 3.3. The HelloMidp application showing an ImageItem .

Handling Textual Input in TextField s

As shown in Table 3.1 , textual input is handled by the class TextField . The constructor of
TextField takes four values: a label, initial text, a maximum text size, and constraints that indicate
the type of input allowed. In addition to avoiding input of illegal characters, the constraints may also
influence the keyboard mode. Several MIDP devices have a numeric keyboard only, and the constraints
allow the application manager to switch the key assignments accordingly. The constants listed in Table
3.3 , declared in the class TextField , are valid constraint values.

Table 3.3. TextField Constraint Constant Values

Constant Value