Assigning an Image object causes nothing to be drawn

Question

I have it set up so all it does is draw a light gray background and some rectangles to create a grid. My next goal was to assign two images so I can default the grid to load as one, and then eventually add some listeners to let me change them to the other.

However, when I assign the image (png format) to the Image object through an ImageIcon (created and assigned previously and creating a new one on the spot were tested) it causes the default background color to be shown, and nothing drawn.

This occurs no matter where I move the assignments to except if I put the assignment into the draw method itself.

The image that I'm trying to use works fine, I pulled it straight from a previously working project, the location hadn't changed. But to be sure, I copied the address and put it in again.

Here is the code (The assignment causing the issue is in Block):

Main:

package BLURGpackage;

import javax.swing.JFrame;

public class Main extends JFrame
{
private final int FRAME_WIDTH = 1200, FRAME_HEIGHT = 1034; // add 34 onto height  
//to show all of the panel

public Main()
{
    setSize(FRAME_WIDTH, FRAME_HEIGHT);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setResizable(false);
    setVisible(true);

    Panel panel = new Panel();

    add(panel);
}

public static void main(String[] args)
{
    Main m = new Main();
}
}

Panel:

package BLURGpackage;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;

import javax.swing.ImageIcon;
import javax.swing.JPanel;

public class Panel extends JPanel implements Runnable
{
public final static int PANEL_WIDTH = 1200, PANEL_HEIGHT = 1000;
private Dimension panelDimension = new Dimension(PANEL_WIDTH, PANEL_HEIGHT);

private Thread panelThread = null;
private boolean threadRunning = false;

private Image dbi = null;
private Graphics dbg = null;

Grid grid;  

private int mouseX = 0, mouseY = 0;
// ============ CHANGE THESE TO CHANGE THE LOCATION OF WHERE THE X AND Y COORDS ARE PRINTED ON THE SCREEN =============
private int printXCoordsX = 10; // X-Coordinate for where to print the current mouse X location
private int printXCoordsY = 855; // Y-Coordinate for where to print the current mouse X location
private int printYCoordsX = printXCoordsX; // X-Coordinate for where to print the current mouse Y location
private int printYCoordsY = printXCoordsY + 15; // Y-Coordinate for where to print the current mouse Y location
// ====================================================================================================================

public Panel()
{   
    grid = new Grid();

    setPreferredSize(panelDimension);
    setBackground(Color.LIGHT_GRAY);


    // ===== Listeners ==========
    addMouseMotionListener(new MouseMotionAdapter()
    {
        public void mouseMoved(MouseEvent e)
        {
            mouseX = e.getX();
            mouseY = e.getY();
        }
    });

    // ====== Start ============= (if startPanel is before listeners, dbi is null... dunno why)
    startPanel();
}

private void startPanel()
{
    if(panelThread == null || threadRunning == false)
    {
        panelThread = new Thread(this);
        threadRunning = true;
        panelThread.start();
    }
    else
        System.out.println("panelThread is NOT null on startup");
}

@Override
public void run() 
{
    while(threadRunning)
    {
        update();
        render();
        paintScreen();
    }
}

public void update()
{
    // Logic here
}

public void render()
{
    if(dbi == null)
    {
        dbi = createImage(PANEL_WIDTH, PANEL_HEIGHT);
        if(dbi == null)
            System.err.println("dbi is NULL");
        else
        {
            dbg = dbi.getGraphics();
        }
    }

    dbg.setColor(Color.LIGHT_GRAY);
    dbg.fillRect(0, 0, PANEL_WIDTH, PANEL_HEIGHT);
    draw(dbg);
}

public void paintScreen()
{
    Graphics g;

    try
    {
        g = this.getGraphics();
        if(dbi != null && g != null)
        {
            g.drawImage(dbi, 0, 0, null);
        }
        Toolkit.getDefaultToolkit().sync();
        g.dispose();
    }catch(Exception e)
    {
        e.printStackTrace();
    }
}

public void draw(Graphics g)
{
    g.setColor(Color.BLACK);
    g.drawString("X: "+mouseX, printXCoordsX, printXCoordsY);
    g.drawString("Y: "+mouseY, printYCoordsX, printYCoordsY);
    // Allow the Grid to draw
    grid.draw(g);
}
}

Grid:

package BLURGpackage;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;

import javax.swing.ImageIcon;

public class Grid 
{
// ======== CHANGE THESE VARIABLES TO CHANGE THE SIZE OF THE GRID =============
public final static int GRID_ROWS = 21, GRID_COLUMNS = 25;
private final int RECT_WIDTH = 48, RECT_HEIGHT = 40;
private final int NUM_BLOCKS = GRID_ROWS*GRID_COLUMNS;

/*public final static int GRID_ROWS = 25, GRID_COLUMNS = 25;
private final int RECT_WIDTH = Panel.PANEL_WIDTH / GRID_ROWS; // 1200 / 25 = 48 px width per rect
private final int RECT_HEIGHT = Panel.PANEL_HEIGHT / GRID_COLUMNS; // 1000 / 25 = 40 px height per rect
private final int NUM_BLOCKS = GRID_ROWS*GRID_COLUMNS;*/
// ============================================================================

private Block[] blockArray;
private int[] blockSelectArray; // numbers for which block is selected. Feed in through file reader

public Grid()
{
    // ===== FOR TESTING ONLY======
    blockArray = new Block[NUM_BLOCKS];
    blockSelectArray = new int[NUM_BLOCKS];

    for(int i=0; i < NUM_BLOCKS; i++)
        {
            blockSelectArray[i] = 0;
        }
    // ============================

    loadBlocks();
}

private void loadBlocks()
{
    int x, y;
    x = y = 0;

    for(int i = 0; i < NUM_BLOCKS; i++)
    {
        if(x >= Panel.PANEL_WIDTH) // if x hits right boundary, reset x and increment y by the px height of a single block
        {
            x = 0;
            y += RECT_HEIGHT;
        }

        blockArray[i] = new Block(blockSelectArray[i], x, y);

        x += RECT_WIDTH;
    }
}

public void draw(Graphics g)
{
    g.setColor(Color.BLACK);
    for(int i=0;i<NUM_BLOCKS;i++)
    {
        g.drawRect(blockArray[i].getBlockX(), blockArray[i].getBlockY(), RECT_WIDTH, RECT_HEIGHT);
        blockArray[i].draw(g);
    }
}


}

Block:

package BLURGpackage;

import java.awt.Graphics;
import java.awt.Image;
import java.awt.Rectangle;

import javax.swing.ImageIcon;

public class Block 
{
private Image blockImage = null;
private Image DIRT_IMG = new ImageIcon("C:/Users/Tyler/workspace/IntTut1/src/thejavahub/images/dirt.png").getImage();
// ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ Problem assignment
private Rectangle blockRect = null;
private boolean solid;

private final int RECT_WIDTH = Panel.PANEL_WIDTH / Grid.GRID_ROWS; // 1200 / 25 = 48 px width per rect
private final int RECT_HEIGHT = Panel.PANEL_HEIGHT / Grid.GRID_COLUMNS; // 1000 / 25 = 40 px height per rect

public Block(int blockNum, int x, int y)
{
    // switch statement on blockNum for what block
    switch(blockNum)
    {
    default:
        System.out.println("Default of switch in Block constrcutor hit");
        break;
    case 0: // background block

        solid = false;
        break;
    case 1: // dirt block 
        blockImage = DIRT_IMG; // <---- uses the assigned image --------
        solid = true;
        break;
    }
    // set the coordinates of the block
    blockRect = new Rectangle(x, y, RECT_WIDTH, RECT_HEIGHT);
}

public void draw(Graphics g)
{
    // draw the image here (.... g.drawImage(blockImage, blockRect.x, blockRect.y, null);   )
    g.drawImage(blockImage, blockRect.x, blockRect.y, null);
}



// ==== GETTERS AND SETTERS ===
public int getBlockX()
{
    return this.blockRect.x;
}

public void setBlockX(int x)
{
    this.blockRect.x = x;
}

public int getBlockY()
{
    return this.blockRect.y;
}

public void setBlockY(int y)
{
    this.blockRect.y = y;
}


public boolean isSolid() {
    return solid;
}


public void setSolid(boolean solid) {
    this.solid = solid;
}




}

First call `setVisible(true);` in the end after adding all the component. — Braj, Jul 17 '14 at 05:44

score 0 · Accepted Answer · edited May 23 '17 at 12:21

Some Points:

Call frame.setVisible(true) in the end after adding all the components.
Use frame.pack() instead of frame.setSize() that fits the components as per component's preferred size.
Override getPreferredSize() to set the preferred size of the JPanel in case of custom painting.
Use Swing Timer instead of Thread that is most suitable for swing application in two ways:
- To perform a task once, after a delay.
- To perform a task repeatedly.
  
  Read more How to Use Swing Timers
Use SwingUtilities.invokeLater() or EventQueue.invokeLater() to make sure that EDT is initialized properly.

Read more

sample code:

private Timer timer;
...

// 1 second delay
timer = new javax.swing.Timer(1000, new ActionListener() {

    @Override
    public void actionPerformed(ActionEvent arg0) {
        // next call
    }
});
timer.setRepeats(true);
timer.start();

public static void main(String args[]) {
    SwingUtilities.invokeLater(new Runnable() {

        @Override
        public void run() {
            Main m = new Main();
        }
    });
}

class MyRoll extends JPanel {
    // override paintComponent in case of custom painting
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        ...
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(..., ...);
    }
}

Thanks! This helped me out a lot! Very well organized answer with links for further reading, thanks! — cyneris, Jul 17 '14 at 08:47

Assigning an Image object causes nothing to be drawn

1 Answers1

Some Points: