Canvas Loading Bar in Java ME

Article Metadata

---

Article

Created: jappit (30 Apr 2008)

Last edited: hamishwillee (07 Feb 2012)

A simple loading bar to be used on Canvas when doing long operations. You can see a live preview here: Canvas Loading bar emulator

We'll start defining some instance variables, that we'll use within our code:

public long stepInterval = 250L;
 
public int width = 0;
public int height = 0;
 
int padding = 0;
 
int color = 0x000000;
 
int squares = 0;
int squareWidth = 0;
 
int currentSquares = 0;
 
Timer stepTimer = null;

Now the bar constructor, with its arguments:

• bar size (width and height)
• padding between squares
• number of squares to be used
• squares color

public LoadingBar(int width, int height, int padding, int squares, int color)
{
	this.width = width;
	this.height = height;
	this.squares = squares;
 
	this.color = color;
	this.padding = padding;
 
	this.squareWidth = (width - padding) / (squares) - padding;
}

Paint method is quite straightforward:

public void paint(Graphics g)
{
	g.setColor(color);
 
	for(int i = 0; i < currentSquares; i++)
	{
		g.fillRect(i * (squareWidth + padding), 0, squareWidth, height);
	}
}

Finally, the animation logic, where we'll use a Timer, and expose start() and stop() methods to control Bar animation:

public void start()
{
	stepTimer = new Timer();
 
	stepTimer.schedule(new TimerTask() 
		{
			public void run()
			{
				step();
			}
		},
		stepInterval, stepInterval
	);
}
public void stop()
{
	stepTimer.cancel();
}
void step()
{
	currentSquares = (currentSquares + 1) % (squares + 1);
}