How To - Create a custom field using attributes of other UI objects

How To - Create a custom field using attributes of other UI objects

Last Updated: 27 March 2009

Article Number: DB-00737

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Summary

This article applies to the following:

BlackBerry® smartphones based on Java® technology

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Details

Using Java technology, you can create a custom field that has a tailored behavior by combining and changing the elements of other UI objects.

The following example shows how to combine the VerticalScrollManagers and EditFields to create a new TextObjectField item. The newly created item is a hybrid of the two items used to create it, allowing for a text box with dimensions set in its constructor - a fixed width and vertical scrolling.

/*
* TextBoxField.java
*/

//Extend VerticalFieldManager to help control scrolling and
//to set a fixed width/height for our field
public class TextBoxField extends VerticalFieldManager {
//Define some variables to be used
//in the class
private int managerWidth;
private int managerHeight;
private EditField editField;

//Pass in the fixed height and width for our object
public TextBoxField(int width, int height) {
//This call to super will help keep the object in place
super(Manager.NO_VERTICAL_SCROLL);
managerWidth = width;
managerHeight = height;

//vfm will allow scrolling within the object
VerticalFieldManager vfm = new VerticalFieldManager(Manager.VERTICAL_SCROLL);

editField = new EditField(){
public void paint(Graphics g) {
//This invalidation will help keep the border clean
//while scrolling
getManager().invalidate();
super.paint(g);
}
};

vfm.add(editField);
add(vfm);
}


public void paint(Graphics g) {
super.paint(g);
//Draw a rectangle around out TextBoxField
g.drawRect(0, 0, getWidth(), getHeight());
}

//If this call to sublayout was made by the system then
//both parameters would be passed with a value of 0.
//This check and adjustment keeps the fixed properties
//maintained.
public void sublayout(int width, int height) {

if (managerWidth == 0) {
managerWidth = width;
}
if (managerHeight == 0) {
managerHeight = height;
}
super.sublayout(managerWidth, managerHeight);
//Force the extent of our manager.
//This will force the height of the object
//where the above super.sublayout() call will
//set the width.
setExtent(managerWidth,managerHeight);
}


//The following two methods allows users of the
//TextBofField read and set its contents.
public String getText() {
return editField.getText();
}

public void setText(String text) {
editField.setText(text);
}
}

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Keywords

Custom field, field, interface, VerticalFieldManager, TextField, TextBox