Custom Text Input in Java ME

Comments

18 Sep
2009

Article Review by Larry101 (20090918)

When using a low-level screen such as a Canvas, the normal UI controls for entering text are not available. As a result, programmers often have to write their own code to mimic the normal text entry components. For this reason, this article provides a useful shell for doing just that. The code example provided implements basic multi-tap text entry (where multiple characters are assigned to each key). The code handles basic functionality, such as clearing letters, caret positioning and handling the delays between button presses (distinguishing between letter switching and moving onto the next letter).

Because this is the type of code programmers often have to write when text entry on a Canvas is required, this article is especially useful. While the code example is far from complete, it provides a useful starting point for programmers wanting to implement similar functionality.

Consider providing some screenshots for how the UI looks with the implementation. Would be a good value add to the article.

Rasika123 - J2ME Keypad

Thank You for this coding and its very helpful to me!I am developing a Sinhala SMS application,and I was entered sinhala Unicode for this code and its working!but i want to apply this code to my application and type that Unicode in a Text field!How can I do that?

Rasika123 08:48, 5 September 2011 (EEST)

Hamishwillee - Written in 1998

I suggest you raise this issue with Jappit (the author) through the private messaging system or raise the query on our discussion boards. There is no guarantee the author is still watching this page. In general we welcome comments, but prefer those which refer to the article itself, not support that you want on your particular project (unless they are going to be relevant to other users reading the article)

Regards

Hamish

hamishwillee 09:04, 5 September 2011 (EEST)

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Article Metadata

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Code Example

Source file: Media:CustomInputMidlet.zip

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Article

Created: jappit (09 Apr 2008)

Last edited: hamishwillee (07 Feb 2012)

Here is a sample Midlet: Media:CustomInputMidlet.zip

Here is a basic example showing how to create a custom text input using Java ME and Canvas, things that is often needed when using low level graphics (e.g. for games).

In this code, you can:

• define which characters map to each key
• define blinking interval
• define max interval between subsequent key presses
• move left/right within the text
• delete text

A lot of features are missing, so if you want to implement them you're welcome :)

package com.jappit.custominput.screen;
 
import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.Font;
import javax.microedition.lcdui.Graphics;
 
public class CustomInputCanvas extends Canvas implements Runnable
{	
	static final char[] KEY_NUM1_CHARS = {'.', '?', '!'};
	static final char[] KEY_NUM2_CHARS = {'a', 'b', 'c'};
	static final char[] KEY_NUM3_CHARS = {'d', 'e', 'f'};
	static final char[] KEY_NUM4_CHARS = {'g', 'h', 'i'};
	static final char[] KEY_NUM5_CHARS = {'j', 'k', 'l'};
	static final char[] KEY_NUM6_CHARS = {'m', 'n', 'o'};
	static final char[] KEY_NUM7_CHARS = {'p', 'q', 'r', 's'};
	static final char[] KEY_NUM8_CHARS = {'t', 'u', 'v'};
	static final char[] KEY_NUM9_CHARS = {'w', 'x', 'y', 'z'};
	static final char[] KEY_NUM0_CHARS = {' '};
 
	int clearKeyCode = Integer.MIN_VALUE;
 
	StringBuffer currentText = new StringBuffer();
	String currentString = new String();
 
	int lastPressedKey = Integer.MIN_VALUE;
	int currentKeyStep = 0;
 
	Font inputFont = null;
	int inputWidth = 0;
	int inputHeight = 0;
	int inputTranslationX = 0;
 
	long lastKeyTimestamp = 0;
	long maxKeyDelay = 500L;
 
	int caretIndex = 0;
	int caretLeft = 0;
	boolean caretBlinkOn = true;
	long caretBlinkDelay = 500L;
	long lastCaretBlink = 0;
 
	boolean goToNextChar = true;
 
	public CustomInputCanvas()
	{
		new Thread(this).start();
 
		inputFont = Font.getDefaultFont();
 
		inputWidth = getWidth();
 
		inputHeight = inputFont.getHeight();
	}
 
	public char[] getChars(int key)
	{
		switch(key)
		{
		case Canvas.KEY_NUM1: return KEY_NUM1_CHARS;
		case Canvas.KEY_NUM2: return KEY_NUM2_CHARS;
		case Canvas.KEY_NUM3: return KEY_NUM3_CHARS;
		case Canvas.KEY_NUM4: return KEY_NUM4_CHARS;
		case Canvas.KEY_NUM5: return KEY_NUM5_CHARS;
		case Canvas.KEY_NUM6: return KEY_NUM6_CHARS;
		case Canvas.KEY_NUM7: return KEY_NUM7_CHARS;
		case Canvas.KEY_NUM8: return KEY_NUM8_CHARS;
		case Canvas.KEY_NUM9: return KEY_NUM9_CHARS;
		case Canvas.KEY_NUM0: return KEY_NUM0_CHARS;
		}
		return null;
	}
	boolean isClearKey(int key)
	{
		return key == -8;
	}
 
	void clearChar()
	{
		if(currentText.length() > 0 && caretIndex > 0)
		{
			caretIndex--;
 
			currentText.deleteCharAt(caretIndex);
 
			currentString = currentText.toString();
		}
	}
	void updateCaretPosition()
	{
		caretLeft = inputFont.substringWidth(currentString, 0, caretIndex);
 
		if(caretLeft + inputTranslationX < 0)
		{
			inputTranslationX = - caretLeft;
		}
		else if(caretLeft + inputTranslationX > inputWidth)
		{
			inputTranslationX = inputWidth - caretLeft;
		}
	}
	public void keyPressed(int key)
	{
		int gameAction = getGameAction(key);
 
		System.out.println("KEY: " + key + ", " + gameAction);
 
		if(isClearKey(key))
		{
			clearChar();
 
			updateCaretPosition();
 
			goToNextChar = true;
		}
		else if(key >= KEY_NUM0 && key <= KEY_NUM9)
		{
			writeKeyPressed(key);
		}
		else if(gameAction == Canvas.LEFT)
		{
			if(caretIndex > 0)
			{
				caretIndex--;
 
				updateCaretPosition();
 
				goToNextChar = true;
			}
		}
		else if(gameAction == Canvas.RIGHT)
		{
			if(caretIndex < currentText.length())
			{
				if(goToNextChar)
					caretIndex++;
 
				updateCaretPosition();
 
				goToNextChar = true;
			}
		}
	}
	public void writeKeyPressed(int key)
	{
		if(goToNextChar || key != lastPressedKey)
		{
			goToNextChar = true;
 
			lastPressedKey = key;
 
			currentKeyStep = 0;
		}
		else
		{
			currentKeyStep++;
		}
 
		char[] chars = getChars(key);
 
		if(chars != null)
		{
			if(currentKeyStep >= chars.length)
			{
				currentKeyStep -= chars.length;
			}
			if(goToNextChar)
			{
				currentText.insert(caretIndex, chars[currentKeyStep]);
 
				caretIndex++;
			}
			else
			{
				currentText.setCharAt(caretIndex - 1, chars[currentKeyStep]);
			}
			currentString = currentText.toString();
 
			updateCaretPosition();
 
			lastKeyTimestamp = System.currentTimeMillis();
 
			goToNextChar = false;
		}
	}
 
	public void checkTimestamps()
	{
		long currentTime = System.currentTimeMillis();
 
		if(lastCaretBlink + caretBlinkDelay < currentTime)
		{
			caretBlinkOn = !caretBlinkOn;
 
			lastCaretBlink = currentTime;
		}
 
		if(!goToNextChar && lastKeyTimestamp + maxKeyDelay < currentTime)
		{
			goToNextChar = true;
		}
	}
 
	public void run()
	{
		while(true)
		{
			checkTimestamps();
 
			repaint();
 
			try
			{
				synchronized(this)
				{
					wait(50L);
				}
			}
			catch(Exception e)
			{
				e.printStackTrace();
			}
		}
	}
 
	public void paint(Graphics g)
	{
		g.setFont(inputFont);
 
		g.setColor(0xffffff);
 
		g.fillRect(0, 0, getWidth(), getHeight());
 
		g.setColor(0x000000);
 
		g.translate(inputTranslationX, 0);
 
		g.drawString(currentString, 0, 0, Graphics.LEFT | Graphics.TOP);
 
		if(caretBlinkOn && goToNextChar)
		{
			g.drawLine(caretLeft, 0, caretLeft, inputHeight);
		}
		g.translate(- inputTranslationX, 0);
	}
}