Displaying a png on screen using AWT

[Matt Shultz]

Hi

I hope someone may help me and clear up my confusion here as I seem to be going round in circles. I am writing an application using Java ME, so would I be right in assuming I can't use any Swing components? I have been trying to take an image saved on my computer and get it to display in a canvas on screen using AWT and I just can't get it to work. The errors I have been getting are ranging from null pointer exceptions when trying to create a graphics object (something I don't fully understand how to do) to the program running in the IDE (which is Eclipse 3.5.2) but just displaying a blank canvas.

here is my code as it stands at the moment:

Panel that holds the canvas:

import java.awt.Image;
import java.awt.Panel;
import java.awt.Toolkit;

public class UIMapScrn extends Panel
{
	private UIMap map;
	private Image image;

	public UIMapScrn()
	{
		image = Toolkit.getDefaultToolkit().getImage("/campusGuide/src/images/campus.png");
		map = new UIMap(image);		
	}
}

Canvas to display picture:

import java.awt.Canvas;
import java.awt.Graphics;
import java.awt.Image;

public class UIMap extends Canvas
{
    private Image image;
    
	public UIMap(Image image)
	{
		super();
		this.image = image;
	}

	public void paint(Graphics g)
	{
		Graphics g2 = g;
		g2.drawImage(image, 0, 0, null);
	}
}

Thanks in advance

[Ulf Dittmer]

You're right that no version of JME supports Swing. But not all flavors of JME support AWT, either. For example, CLDC and MIDP don't - you need at least the CDC Personal (Basis) Profile for AWT to be available.

[Matt Shultz]

My compiler compliance level is set to 1.3 and the currently installed compiler is 1.6.
Also other AWT components are working elsewhere in the program
i.e.:

import java.awt.Button;
import java.awt.Choice;
import java.awt.GridLayout;
import java.awt.Label;
import java.awt.Panel;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;

[Matt Shultz]

I have changed the code to the following and now the frame displays, the g.toString() method displays a Graphics "string" in the console but the picture still doesn't display on the screen!
I think I am going to cry!

import java.awt.Graphics;
import java.awt.Panel;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;

public class UIMapScrn extends Panel
{
	private UIMap map;
	private File img;
	private BufferedImage bimg;
	private Graphics g;

	public UIMapScrn()
	{
		img = new File("/campusGuide/src/images/campus.png");
		try
		{
			bimg = ImageIO.read(img);
		}catch(IOException e)
		{
			e.printStackTrace();
		}
		map = new UIMap(bimg);
	}
	
	public void paintScrn()
	{
		g = bimg.createGraphics();
		System.out.println(g.toString());
		map.paint(g);
		map.setVisible(true);
	}
}

import java.awt.Canvas;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;

public class UIMap extends Canvas
{
    private BufferedImage bimg;
    
	public UIMap(BufferedImage bimg)
	{
		super();
		this.bimg = bimg;
	}

	public void paint(Graphics g)
	{
		Graphics2D g2 = (Graphics2D) g;
		g2.drawImage(bimg, null, 0, 0);
	}
}

Can anyone help???

[Rob Spoor]

1) call super.paint(g) as the first line of UIMap.paint

2) you need to add the map variable to the panel. At the moment, paintScrn() only paints the map variable to a buffered image. That image is not shown in the user interface at the moment.

You are also aware that bimg will be drawing itself onto itself when you call paintScrn()?

[Matt Shultz]

Hi

Thanks for your reply I am obviously very confused here as I wasn't aware bimg was drawing itself on itself, which line does this?

I have tried making your suggested changes but it still doesn't work just a blank screen as shown in the screenshot.

[Rob Spoor]

Matt Shultz wrote:I wasn't aware bimg was drawing itself on itself, which line does this?

...
bimg = ImageIO.read(img);   
...
map = new UIMap(bimg);   
...
g = bimg.createGraphics();   
...
map.paint(g);

this.bimg = bimg;   
...
g2.drawImage(bimg, null, 0, 0);

The bimg of the above code block is the same as the bimg of the below code block. You create a graphics object for this image, then pass this to map.paint. That paint draws bimg onto that graphics object - which is the graphics object of bimg itself.

I have tried making your suggested changes but it still doesn't work just a blank screen as shown in the screenshot.

How have you added the map to the Panel?

[Matt Shultz]

I tried this,
new code listing:

import java.awt.Graphics;
import java.awt.Panel;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;

public class UIMapScrn extends Panel
{
	private UIMap map;
	private File img;
	private BufferedImage bimg;
	private Graphics g;

	public UIMapScrn()
	{
		img = new File("/Users/stevenbrown/Documents/workspace/2015/campusGuide/src/images/campus.png");
		try
		{
			bimg = ImageIO.read(img);
		}catch(IOException e)
		{
			e.printStackTrace();
		}
		map = new UIMap(bimg);
		this.add(map);
	}
	
	public void paintScrn()
	{
		g = bimg.createGraphics();
		System.out.println(g.toString());
		map.paint(g);
		map.setVisible(true);
	}
}

import java.awt.Canvas;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;

public class UIMap extends Canvas
{
    private BufferedImage bimg;
    
	public UIMap(BufferedImage bimg)
	{
		super();
		this.bimg = bimg;
	}

	public void paint(Graphics g)
	{
		super.paint(g);
		Graphics2D g2 = (Graphics2D) g;
		g2.drawImage(bimg, null, 0, 0);
	}
}

[Rob Spoor]

A bit of debugging showed me that the preferred size of the Canvas is 0x0 pixels. It is added but it has no size.

Change your constructor to this:

    public UIMap(BufferedImage bimg)
    {
        super();
        setPreferredSize(new Dimension(bimg.getWidth(), bimg.getHeight()));
        this.bimg = bimg;
    }

This extra line sets the preferred size to be that of the image to display. This preferred size is then used by the Panel's layout manager (a FlowLayout) to determine its preferred size.

[Matt Shultz]

That has sorted it , thanks you sooooo much .
I can't begin to explain how grateful I am
You are a star!

[Rob Spoor]

You're welcome.