Develop Reference

How can a JPanel be changed after added to JFrame?

I have created a subclass of JPanel to display images. I instantiate this in the constructor of a JFrame and add it to that JFrame. This works perfectly. Then I have added a button with an ActionListener to change that Image. My problem is that the JFrame won´t update although I have tried repainting etc.
The subclass of JPanel:
public class ImagePanel extends JPanel {
BufferedImage bf;
public ImagePanel(String dateiname)
{
try {
bf = ImageIO.read(new File(dateiname));
} catch (IOException e) {
e.printStackTrace();
}
}
public void paint(Graphics g)
{
g.drawImage(bf.getScaledInstance(300,200,1),0,0,null );
}
}
The JFrame is basically this
public class Hauptfenster extends JFrame {
private JButton changeImage;
private JPanel buttonPanel;
private ImagePanel ip;
public Hauptfenster {
ip = new ImagePanel("first_image.jpg");
buttonPanel = new JPanel();
buttonPanel.add(changeImage);
changeImage.addActionListener((e) -> {
ip = new ImagePanel("new_image.jpg");
ip.setVisible(true);
});
this.add(buttonPanel);
this.add(ip);
this.setVisible(true);
}
}
Why doesn´t the method in the ActionListener update the ip component in the JFrame Hauptfenster?

When you do ip = new ImagePanel("new_image.jpg"); you're creating a whole new ImagePanel that has nothing to do with your current layout. You could.
remove(ip);
ip = new ImagePanel("new_image.jpg");
add(ip);
repaint();
Another way you could do it is to just change the buffered image.
Add the following method to your image panel.
public void loadImage(String dateiname) {
try {
bf = ImageIO.read(new File(dateiname));
} catch (IOException e) {
e.printStackTrace();
}
}
Then in your action listener.
ip.loadNewImage("new_image.jpg");
ip.repaint();
You have a bunch of bad habits going on in your code though.
Such as, override paintComponent instead of paint and it should look like.
#Override
public void paintComponent(Graphics g){
super.paintComponent(g);
g.drawImage(bf.getScaledInstance(300,200,1),0,0,null );
}
That way transparency will be handled correctly.
You shouldn't extend JFrame, you should just create a JFrame.
When you add components, you there is a layout manager involved. It's good to be aware of that and handle things accordingly. I would change your constructor to.
public Hauptfenster() {
JFrame frame = new JFrame();
ip = new ImagePanel("first_image.jpg");
buttonPanel = new JPanel();
changeImage = new JButton("change image");
buttonPanel.add(changeImage);
changeImage.addActionListener((e) -> {
frame.remove(ip);
ip = new ImagePanel("new_image.jpg");
frame.add(ip, BorderLayout.CENTER);
frame.repaint();
});
frame.add(buttonPanel, BorderLayout.SOUTH);
frame.add(ip, BorderLayout.CENTER);
frame.setVisible(true);
}
If you need more help, you'll need to actually make your example compilable. There are too many errors right now.

Is there ever a reason drawImage won't actually draw an image?

private void renderLevelBackground(Graphics2D g2) {
Image backgroundImage = model.getBackgroundImage();
g2.drawImage(backgroundImage, 0, 0, null);
}
This is my code, I know that the backgroundImage is loaded properly because if I getWidth/Height it gives me the correct values. Is there anyway to test if it's the image or if it's the method somehow? It just won't draw on my screen despite the fact that I've used the drawImage method many times in this project already, all of which work flawlessly.
Thanks

"Is there ever a reason drawImage won't actually draw an image?"
Possibility, there is no image due to a bad path provided. Use ImageIO.read() which will cause an exception if the image file is not found. For example
public class ImagePanel extends JPanel {
private BufferedImage image;
public ImagePanel() {
try {
image = ImageIO.read(getClass().getResource("/resources/image.png"));
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
If the image is not found, it will throw an IO exception.
Possibility, the panel to which you are drawing, has no preferred size (0 x 0), and you are adding it a container wit layout that respects preferred sizes, so the ImagePanel will not be able to show the image. For example
public class ImagePanel extends JPanel {
protected void paintComponent(...) {
...
}
JPanel panel = new JPanel(); // default FlowLayout that respects preferred sizes
panel.add(new ImagePanel());
To fix this, you can override the gerPreferredSize() of the ImagePanel
public class ImagePanel extends JPanel {
#Override
public Dimension getPreferredSize() {
return new Dimension(300, 300);
}
}
Possibility, you are not calling your method within the graphics context of the paint[Component] method.
protected void paintComponent(Graphics 2d) {
super.paintComponent(g);
Grapchics2D g2 = (Graphics2D)g;
renderLevelBackground(g2);
}
Other than that, these are all just guesses, and you should provide some more code code (preferably an MCVE) to help us better help you with the problem.
Possible Alternative to your approach. It seems like (from the little code snippet and it method signature semantics) you want to change the background image, when a level have changed. Consider using setBackgroundImage(BufferedImage image) method in your panel class, when the image is drawn. You can then set the background, whenever need be. Something like
public class BackgroundPanel extends JPanel {
private BufferedImage backgroundImage;
public void setBackgroundImage(BufferedImage image) {
this.backgroundImage = image;
repaint();
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Grpahics2D g2 = (Graphics2D)g;
if (image != null) {
g2.drawImage(backgroundImage, 0, 0, this);
}
}
}
So whenever you call setBackgroundImage, the image will change, and be repainted.

You may need to explicitly tell the JComponent that you are painting onto that it needs to be redrawn with revalidate() and repaint()

Subtle differences between java swing objects

I am having some difficulty figuring out why there is a difference between the results I see on the Title Screen and the Setup Screen. I copy/pasted the majority of the code before tweaking each... it clearly has to do with something in my outer frame, but I don't know what. The problem I am seeing is that although the Title Screen comes up at the correct size of 1024x768 with the background correctly displayed, the Setup Screen comes up as a very small window as though I had not just set it's size. The background image is also only shown in that sliver of space, even if the box is resized.
I have removed all of the elements inside of Title Screen but it still maintains its size. Can someone help? Thanks
OuterFrame
public class OuterFrame extends JFrame {
public OuterFrame(String windowHeading) {
int WIDTH = 1024;
int HEIGHT = 768;
final Dimension screenSize = new Dimension(WIDTH,HEIGHT);
setDefaultCloseOperation(DISPOSE_ON_CLOSE);
JPanel title = new TitleScreen();
title.setLayout(new BoxLayout(title, BoxLayout.PAGE_AXIS));
JButton matchButton = new JButton("New Match");
//Add action listener to button
matchButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
//Execute when button is pressed
removeAll();
JPanel setupScreen = new SetupScreen();
add(setupScreen);
pack();
}
});
JButton exitButton = new JButton("Exit to Windows");
//Add action listener to button
exitButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
//Execute when button is pressed
System.exit(0);
}
});
matchButton.setAlignmentX(title.CENTER_ALIGNMENT);
exitButton.setAlignmentX(title.CENTER_ALIGNMENT);
title.setPreferredSize(screenSize);
title.add(matchButton);
title.add(Box.createRigidArea(new Dimension(0,25)));
title.add(exitButton);
add(title);
pack();
}
}
Title Screen
public class TitleScreen extends JPanel {
public BufferedImage background;
public TitleScreen() {
try {
InputStream is = new BufferedInputStream(new FileInputStream("images/datascreen.png"));
Image image = ImageIO.read(is);
background = (BufferedImage)image;
} catch (Exception a) {
}
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D)g;
g2.drawImage(background,0,0,1024,768,null);
}
}
SetupScreen
public class SetupScreen extends JPanel {
public BufferedImage background;
public SetupScreen() {
try {
InputStream is = new BufferedInputStream(new FileInputStream("images/datascreen.png"));
Image image = ImageIO.read(is);
background = (BufferedImage)image;
} catch (Exception a) {
}
setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D)g;
g2.drawImage(background,0,0,1024,768,null);
}
}
Sorry about the formatting.. I can't for the life of me make it keep the indention I use in my code.
Edit:
#Override
public Dimension getPreferredSize() {
return new Dimension(1024, 768);
}
I added the above to both the title and the setup classes, as well as removing the hard coded resize. The issue still occurs - the window is sized correctly for the title but not the setup. Any help would be appreciated..

Read the Swing tutorial on Custom Painting for the basics. In this case the problem is that you don't override the getPreferredSize() method of your custom component, so the layout manager basically uses 0.
The reason your first screen displays is because you hardcoded:
title.setPreferredSize(screenSize);
This is a no-no (for too many reasons to go into detail here). The component should return its preferred size as mentioned above and then the pack() statement will work properly.

Figured out that the problem was the removeAll() statement. I added getContentPane. to it and it worked fine.

Display multiple images in a single applet

I have to build a small Java applet for a project. I have previously never used applets. Hence I don't know much about the various inbuilt functions available. The layout of this applet is as below:
The screen is divided into 3 parts
Top most part will have a set of buttons and text boxes
Middle part and bottom part will be displaying different images
These Images can vary in size when the program is run each time (Hence it requires scroll bars in case the image goes out of the screen)
Till now I have succeeded in partitioning the screen and creating separate panels for the each part and adding the corresponding components in them.
Problem:
The bottom image is not completely visible. And also scroll bars are not appearing for each Image when it does not fit into the panel.
I tried using setSize(), setMinimumSize() methods but it does not produce any changes in the output. Can you please help me with the above problem?
This is what I have done till now:
/*<applet code=DOSlayout.java width=400 height=400>
</applet>*/
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class DOSlayout extends JApplet implements ActionListener {
Button ViewButton;
Panel1 Top;
Panel2 LeftSide;
Panel3 RightSide;
Label l1,l2,l3;
Image img;
public void init() {
setSize(400,400);
setLayout(new BorderLayout());
Top = new Panel1();
LeftSide = new Panel2();
RightSide = new Panel3();
Top.setSize(getSize().width, getSize().height/3);
LeftSide.setSize(getSize().width,getSize().height/3);
RightSide.setSize(getSize().width,getSize().height/3);
//RightSide.setMinimumSize (new Dimension(400, 10000));
add(Top, BorderLayout.NORTH);
add(LeftSide, BorderLayout.CENTER);
add(RightSide, BorderLayout.SOUTH);
ViewButton = new Button("View");
l1 = new Label("North");
l2 = new Label("East");
l3 = new Label("West");
Top.add(ViewButton);
Top.add(l1);
//LeftSide.add(l2);
//RightSide.add(l3);
ViewButton.addActionListener(this);
}
#Override
public void actionPerformed(ActionEvent arg0) {
// TODO Auto-generated method stub
}
class Panel1 extends JPanel {
Panel1() {
super();
}
public void paint(Graphics g) {
}
}
class Panel2 extends JPanel {
Panel2() {
super();
}
private Image img;
public void init()
{
img = null;
}
public void loadImage()
{
try
{
img = getImage(getCodeBase(), "input1.png");
}
catch(Exception e) { }
}
public void paint(Graphics g)
{
if (img == null)
loadImage();
g.drawImage(img, 0, 0, this);
//g.drawImage(img,0,0,(int)getBounds().getWidth(), (int)getBounds().getHeight(),this);
}
}
class Panel3 extends JPanel {
Panel3() {
super();
}
private Image img;
public void init()
{
img = null;
//setSize(400,400);
}
public void loadImage()
{
try
{
img = getImage(getCodeBase(), "input2.png");
}
catch(Exception e) { }
}
public void paint(Graphics g)
{
if (img == null)
loadImage();
g.drawImage(img, 0, 0, this);
//g.drawImage(img,0,0,(int)getBounds().getWidth(), (int)getBounds().getHeight(),this);
}
}}

Start with the container used in ImageViewer. It centers the image inside a scroll-pane whose scroll-bars appear reliably.
Further tips
"I have previously never used applets." That is ominous, given applets are tougher to develop & deploy than frames. I suggest develop this first in a JFrame (then launch the frame from a link using Java Web Start). Only after seeing the frame launched using JWS should you consider using an applet. By that stage, any 'conversion' needed will be much simpler.
Don't ever call setSize(..) in an applet. The size is in the HTML.
Don't mix Swing and AWT components unless necessary, use all Swing.
It is typically a bad idea to set the sizes (preferred, max or min) of any components.
Please learn common Java naming conventions (specifically the case used for the names) for class, method & attribute names & use it consistently.

Why slideshow not working in Java using Swing and Awt?

I am doing slideshow of images program in java using timer.
In timer event listner i have added code to chnage image but image is not changing.
Below is the code i have written
class ImagePanel extends JPanel {
private Image backgroundImage;
public ImagePanel(Image backgroundImage) {
super();
this.backgroundImage = backgroundImage;
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(this.backgroundImage, 0, 0, null);
}
}
public class A extends JFrame{
static int counter;
List<String> imagePaths;
int nimgpaths=0;
static A frame = new A();
public static void main(String[] args) {
frame.setSize(1024, 768);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getPath();
/* Getting required image */
Image backgroundImage = null;
String pathToTheImage = "C:\\Documents and Settings\\Administrator\\My Documents\\My Pictures\\civ1.JPG";
try {
backgroundImage = ImageIO.read(new File(pathToTheImage));
} catch (IOException e) {
e.printStackTrace();
}
/* Initializing panel with the our image */
ImagePanel panel = new ImagePanel(backgroundImage);
frame.getContentPane().add(panel);
frame.setVisible(true);
frame.timerEvent();
//frame.show();
}
public void timerEvent(){
Timer timer = new Timer(5000, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
System.out.println("Time event occured");
if(counter > nimgpaths)
counter=0;
String imgPath=imagePaths.get(counter);
Image backgroundImage = null;
try {
backgroundImage = ImageIO.read(new File(imgPath));
}catch (Exception e1) {
e1.printStackTrace();
}
/* Initializing panel with the our image */
frame.removeAll();
ImagePanel panel = new ImagePanel(backgroundImage);
panel.repaint();
//panel.setBackground(backgroundImage);
frame.getContentPane().add(panel);
}
});
timer.start();
}
// To get path of images
public void getPath(){
DbOps db=new DbOps();
imagePaths=db.getPath();
nimgpaths=imagePaths.size();
for(Iterator i=imagePaths.iterator();i.hasNext();){
System.out.println((String)i.next());
}
}
}

Why are you using a custom panel and painting?
Your code is simply painting the image at its preferred size. This functionality is available when you use a JLabel. Then when you use the label all you need to do is use:
label.setIcon(....);
when you want to change the image. Read the section from the Swing tutorial on How to Use Icons for more information.
The only reason to create a custom component is if you plan to scale the image or do something fancy like that. If this is the case then you can use something like the Background Panel which supports scaled images as well as a setImage() method so you can change the image dynamically.

A much better design for ImagePanel would let you just replace the image, rather than removing the component. If you do have to replace a visible component, though, you have to call validate() on its container, or the new one isn't going to show up (most of the time, anyway.) I think that's your problem here.

frame.removeAll() is not doing what you would expect - it is removing the components from the frame itself rather than removing the components from the content pane of the frame. Change the code at the end of the timer's action listener to something like this to fix it:
ImagePanel panel = new ImagePanel(backgroundImage);
frame.getContentPane().removeAll();
frame.getContentPane().add(panel);
frame.getContentPane().invalidate();
frame.getContentPane().validate();

Your concept itself is wrong.
You can refresh the panel like so:
public void refreshPanel(JPanel panel){
panel.removeAll();
panel.invalidate();
panel.validate();
}
Problem:
I see in your code that you are trying to create more than one object of the same panel, which you need to refresh.
It would be better to create one panel object and refresh that object.
ImagePanel panel = new ImagePanel(backgroundImage);
Hope you can understand what I wanted to explain to you.
If you are still confused then let me know.