New Details:
Repaint method of my JPanel object does not work when called from inside actionPerformed event of my main class. It DOES work inside the ImageViewer method of the main class ImageViewer but does not work inide the actionPerformed method of this class.
These are the essential parts of my code which are not working properly ( repainting part ):
Main Class:
/**
* #(#)NeatImageViewer.java
*
* NeatImageViewer application
*
* #author
* #version 1.00 2010/11/1
*/
import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import java.io.*;
import javax.imageio.*;
import javax.swing.*;
public class NeatImageViewer extends JFrame implements ActionListener {
GraphicsPanel gp;
NeatImageViewer() {
//... window components ...
}
public static void main(String[] args) {
NeatImageViewer niv = new NeatImageViewer();
niv.setSize(500,500);
niv.setLocationRelativeTo(niv);
niv.setVisible(true);
}
public void actionPerformed(ActionEvent e) {
//...
gp = new GraphicsPanel();
gp.img = img;
gp.repaint(); //<!--- Not Working!
this.add(gp);
//...
}
}
GraphicsPanel Class:
/**
* #(#)GraphicsPanel.java
*
*
* #author
* #version 1.00 2010/11/1
*/
import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import java.io.*;
import javax.imageio.*;
import javax.swing.*;
public class GraphicsPanel extends JPanel {
BufferedImage img;
GraphicsPanel() {
super();
}
protected void paintComponent(Graphics g) {
//paint method isn't executed???
super.paintComponent(g);
System.out.println("Paint!");
}
}
You have to override paintComponent(Graphics g) instead of paint(Graphics g).
So, the method you posted should be renamed to paintComponent.
EDIT: Have you pack()'ed your frame when your initialization is done?
EDIT: The repaint() method does nothing when the component isn't visible. So, you have to add it first to the JFrame, pack() the frame. After packing it, repainting isn't needed anymore.
In Swing you don't use a Canvas. You do custom painting on a JPanel or JComponent and you override the paintComponent(...) method as already stated. Read the Swing tutorial on Custom Painting for more information and working examples.
Also, with Swing there is no need to create a custom components to show an image. You just use a JLabel with an ImageIcon. Read the section on "How to Use Icons".
Bookmark the tutorial for all the Swing basics.
Edit:
When you add a component to a visible GUI the basic code should be:
panel.add( ... );
panel.revalidate();
panel.repaint();
(I'm Skyfe but from another IP so ain't "logged in" and couldn't comment)
I'm sorry but I don't get what's the problem???
I offered my code and it is NOT executing the paintComponent function upon calling repaint from the actionPerformed method. Just copy paste my code and compile it with a java compiler and it does NOT execute the paintComponent method upon performing an action which I can tell because I used a System.out.println() method inside the paint method. And no it does not paint anything because I'm just trying to check whether it calls the paint method AT ALL because I put a system output inside the paintComponent method which is not executed when using repaint. It was just a test and it didn't work.
So what you mean by where is the SSCCE, this is all the code I have. I compiled exactly the code I posted in my main post and the problem with it is that it does not show any system output when an action was performed ( and the repaint event was called ). I fail to see what misses in my post?
Related
First class
package com.mudd.render;
import java.awt.Dimension;
import javax.swing.JFrame;
import com.mudd.game.Game;
public class render {
int width = 500;
int height = 600;
Game g = new Game();
public void show(){
JFrame gameWindow = new JFrame("..");
gameWindow.setPreferredSize(new Dimension(width, height));
//gameWindow.setIconImage(new ImageIcon(imgURL).getImage());
gameWindow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
gameWindow.pack();
gameWindow.add(g);
gameWindow.setVisible(true);
}
public static void main(String[] args) {
render game = new render();
game.show();
}
}
Second class
package com.mudd.game;
import java.awt.Graphics;
import javax.swing.JPanel;
#SuppressWarnings("serial")
public class Game extends JPanel {
public void paint(Graphics g){
g.fillOval(10, 10, 500, 500);
System.out.println("Test");
}
}
What is causing my Test print statement to be printed twice? If I add other priintlns it will also print them both out. I've been learning Java from Head First Java and I've done other small command line projects but nothing like this has ever happened to me.
Swing graphics are passive -- you don't call the painting methods directly yourself, but rather the JVM calls them. They are sometimes possibly called at your suggestion such as when you call repaint() but even this is never a guarantee, and they are sometimes possibly called at the suggestion of the platform, such as when it determines that your application has "dirty" pixels that need cleaning. So you have to plan for this -- the painting method should contain no code that changes the state of the object nor should it contain business logic code. Instead it should have code for painting and nothing more.
For more details on this, please see:
Lesson: Performing Custom Painting: introductory tutorial to Swing graphics
Painting in AWT and Swing: advanced tutorial on Swing graphics
Side recommendations:
Override the JPanel's paintComponent method, not its paint method
Use the #Override annotation for any method override
Don't forget to call the super's method in your override.
In this video drawing() method is called in main class. When we remove drawing() in the main method it still draws the shape. How can we avoid this situation ?
shapes class:
import java.awt.*;
import javax.swing.*;
public class shapes{
public static void main(String[] args){
JFrame frame = new JFrame("Test");
frame.setVisible(true);
frame.setSize(400,200);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
draw object = new draw();
frame.add(object);
object.drawing();
}
}
Draw class:
import java.awt.*;
import javax.swing.*;
public class draw extends JPanel{
public void drawing(){
repaint();
}
public void paintComponent(){
super.paintComponent(g);
g.setColor(Color.BLUE);
g.fillRect(10,15,100,100);
}
}
There are some minor issues with the code, but I assume that it's only a small snippet for demonstration purposes. For details, have a look at Performing Custom Painting.
Actually, this tutorial would also answer your question, but to summarize it:
The paintComponent method will be called automatically, "by the operating system", whenever the component has to be repainted. The call to repaint() only tells the operating system to call paintComponent again, as soon as possible. So you can call repaint() to make sure that something that you canged appears on the screen as soon as possible.
If you explicitly want to enable/disable certain painting operations, you can not influence this by preventing paintComponent from being called. It will be called anyhow. Instead, you'll introduce some flag or state indicating whether something should be painted or not.
In your example, this could roughly be done like this:
import java.awt.*;
import javax.swing.*;
public class Draw extends JPanel{
private boolean paintRectangle = false;
void setPaintRectangle(boolean p) {
paintRectangle = p;
repaint();
}
#Override
public void paintComponent(){
super.paintComponent(g);
if (paintRectangle) {
g.setColor(Color.BLUE);
g.fillRect(10,15,100,100);
}
}
}
You can then call the setPaintRectangle method to indicate whether the rectangle should be painted or not.
I am new to graphics.
I got this code from open source.It should paint String "HEeelo" on jframe,but it does not.Can anyone explain why it is not working properly and the principle of paint method?Why should it edit JFrame as it is just method which is not even called from main?
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.KeyAdapter;
import javax.swing.JFrame;
public class view extends JFrame{
public view(){
this.setSize(new Dimension(250, 250));
this.setVisible(true);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public void paint(Graphics g){
g.drawString("heello", 10, 10);
}
public static void main(String []args){
new view();
}
}
Get rid of that tutorial, that is not the way to do painting.
First the basic problems are that you should always invoke super.paint(...) when overriding a method. Secondly the text won't show because it is being painted under the title bar. You need to increase the y offset:
super.paint(g);
g.drawString("heello", 10, 40);
and the principle of paint method
Read the section from the Swing tutorial on Custom Painting for the proper way to do this. Basically you override the paintComponent() method of a JPanel and then add the panel to the frame. You should not do custom painting on a frame directly.
I've created an applet game, but when I modify some of the contents, I need to (maximise or minimise) resize the window to show my modified applet.
even when I add a label, or anything, it needs resizing since I've not used the paint method.(no use of repaint).
Help me with this, how to show modified contents without resizing...
here's a sample code that have same problem.
import java.awt.Button;
import java.awt.FlowLayout;
import java.awt.Label;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JApplet;
public class Appl extends JApplet implements ActionListener{
Button b = new Button();
public void init()
{
setLayout(new FlowLayout());
setSize(300,300);
setVisible(true);
add(b);
b.addActionListener(this);
}
public void actionPerformed(ActionEvent e) {
if(e.getSource()==b)
{
add(new Label("Button clicked"));
repaint();
}
}
}
If I remember correctly you just call the repaint method after the modifications of your content, then it should show up.
Repaint is always implicitly called when you resize the Applet.
Edit: Applying the validate medthod on the Japplet Container works for me in the given example. This also redraws added components, repaint just calls the paint method. try it :-)
I have a custom class that extends JLabel. For specific instances of that class, I want to add some spacing to the text on the left side. I need the spacing as I'm setting the background of this JLabel and I don't want the text to bump up right next to the edge of the colored background. I fished around quite a bit and implemented this (inside the paint function):
if (condition) {
bgColor = Color.red;
setBackground(bgColor);
setOpaque(true);
// This line merely adds some padding on the left
setBorder(BorderFactory.createEmptyBorder(0, 10, 0, 0));
}
else {
setOpaque(false);
}
This appears to work in that it adds the spacing I want, however it has an unfortunate side effect in that it appears to break the repainting of the whole rest of the application...it appears that only that particular component is repainting and not the rest of the application. I eventually tracked it down to the setBorder call specifically...setting ANY kind of border appears to cause the same broken behavior. We have two different versions of our application, one that runs in Java 1.5 and one that runs in Java 1.6, the Java 1.6 version appears to work correctly while the Java 1.5 version doesn't. It is not possible to upgrade the older version to Java 1.6...I need something that will work in Java 1.5. Also, I tried this (just to see what it looked like):
setHorizontalTextPosition(JLabel.CENTER);
And that also appears to break the repainting in exactly the same way. I looked through the source of our application and found other places where we set borders (including empty borders), but couldn't find any on JLabels (only panels, buttons, etc). Anybody see anything like this before? Know how to fix it? Or perhaps another way to obtain the spacing I require that may work around the bug? Thanks.
The problem is that you're calling that code inside the paint method. You should not do that because it will freeze the EDT with unwanted loops in the swing painting pipeline.
You should put that code on the constructor and change the component design state elsewhere on the app life cycle.
If you want to know a little bit more about Swing painting please read the "Swing painting pipeline" post on pushing-pixels.org.
Note that you can use BorderFactory.createCompoundBorder to combine any two borders. Then you can set spacing with the emptyBorder and any other to draw the outer border.
EDIT: Example added.
package com.stackoverflow.swing.paintpipeline;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
import javax.swing.border.Border;
public class JLabelSetBorderPaintProblem extends JLabel {
public JLabelSetBorderPaintProblem(String text) {
super(text);
}
/*
* #see javax.swing.JComponent paint(java.awt.Graphics)
*/
#Override
public void paint(Graphics g) {
super.paint(g);
// You can not call setBorder here.
// Please check javadoc.
}
/*
* #see javax.swing.JComponent paintBorder(java.awt.Graphics)
*/
#Override
protected void paintBorder(Graphics g) {
super.paintBorder(g);
// Here is where the Swing painting pipeline draws the current border
// for the JLabel instance.
// Please check javadoc.
}
// Start me here!
public static void main(String[] args) {
// SetBorder will dispatch an event to Event Dispatcher Thread to draw the
// new border around the component - you must call setBorder inside EDT.
// Swing rule 1.
SwingUtilities.invokeLater(new Runnable() {
#Override public void run() {
// Inside EDT
JFrame frame = new JFrame("JLabel setBorder example");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Add the JLabel
final JLabelSetBorderPaintProblem label = new JLabelSetBorderPaintProblem("Just press or wait...");
frame.add(label);
// And change the border...
label.addMouseListener(new MouseAdapter() {
#Override public void mousePressed(MouseEvent e) {
label.setBorder(BORDERS.get(new Random().nextInt(BORDERS.size())));
}
});
// ...whenever you want
new Timer(5000, new ActionListener() {
#Override public void actionPerformed(ActionEvent e) {
label.setBorder(BORDERS.get(new Random().nextInt(BORDERS.size())));
}
}).start();
frame.pack();
frame.setVisible(true);
}
});
}
public static final List<Border> BORDERS;
static {
BORDERS = new ArrayList<Border>();
BORDERS.add(BorderFactory.createLineBorder(Color.BLACK));
BORDERS.add(BorderFactory.createLineBorder(Color.RED));
BORDERS.add(BorderFactory.createEtchedBorder());
BORDERS.add(BorderFactory.createTitledBorder("A border"));
}
}