Develop Reference

Invisible objects because repaint method - Java Swing

The problem comes because I overwrite the paintComponent method of a jPanel, so when I repaint all the objets are hidden till I focus them.
I need to overwrite the paintComponent method cause it's the only one answer I'd found in internet to change the background image of a jFrame.
So firstly I create a jPanel class:
public class JPanelFondoPrincipal extends javax.swing.JPanel {
public JPanelFondoPrincipal(){
this.setSize(800,500);
}
#Override
public void paintComponent(Graphics g){
super.paintComponent(g);
Dimension tamanio = getSize();
ImageIcon imagenFondo = new ImageIcon(getClass().getResource("/images/fondo_principal.png"));
g.drawImage(imagenFondo.getImage(),0,0,tamanio.width, tamanio.height, null);
setOpaque(false);
}
}
And in my jPanelForm:
private void formWindowOpened(java.awt.event.WindowEvent evt) {
// TODO add your handling code here:
JPanelFondo p = new JPanelFondo();
this.add(p);
validate();
p.repaint();
}
I'd already tried to add all my Objets (labels, textFields...) to a new Panel so I can add it after repaint, and set all the objets visibles manually but everything is still invisible.
Many thanks, I need to finish the app in 6 days and I'm getting crazy by the minute
EDIT: SOLVED THANKS TO CARDLAYOUT

don't add / remove JPanels or its contents on runtime, use CardLayout instead
your JPanelFondo p = new JPanelFondo(); doesn't corresponding somehow with public class JPanelFondoPrincipal extends javax.swing.JPanel {
for better help sooner edit your question with an SSCCE,

Swing programs should override paintComponent() instead of overriding paint().
http://java.sun.com/products/jfc/tsc/articles/painting/
And you should call super.paintComponent(g); first in overriden paintComponent();
public void paintComponent(Graphics g){
super.paintComponent(g);
Dimension tamanio = getSize();
ImageIcon imagenFondo = new ImageIcon(getClass().getResource("/images/fondo_principal.png"));
g.drawImage(imagenFondo.getImage(),0,0,tamanio.width, tamanio.height, null);
setOpaque(false);
}
Here's the proper way to handle painting onto JPanel component.

JButton is drawing behind an image

I am making a starting screen, and it's working out pretty fine, got a background image when it starts, now I am trying to draw a JButton on the startmenu, which is a JFrame. But when I run my program, the button appears behind the background picture. If I hover above the area where the button is placed, it's flickering, and when I click it that happens too. Is there any way to draw the Button INFRONT of the background? I made the button as last in the code. My code to draw the background and button:
public void drawStartScreen(){
startScreenOn = true;
Graphics2D b = buffer.createGraphics();
b.setColor( Color.WHITE );
b.fillRect(0, 0, 800, 600);
b.drawImage(start,0,0,null);
setLayout( null );
button = new JButton("Start Game");
button.setBounds(10,10,100,100);
button.setVisible( true );
add(button);
}
It draws the image first, and then the Button, but the button still draws behind the image.

You are mixing painting and adding of components and you definitely shouldn't be doing this. Instead add components when you create the screen or when you first need them but make sure you are only doing this once. Then separate modify the components that need painting changes inside the paintComponent() method.

I recommend you'd use a JLayeredPane (I go for custom painting only as a last resort).
If you're still interested in mixing the 'low-level' painting with 'higher-level' JComponent hierarchy, look at a question about a JFrame that has multiple layers.

Override the paint method on the JFrame:
#Override
public void paint(Graphics g) {
super.paint(g);
Graphics2D b = (Graphics2D)g;
b.setColor( Color.WHITE );
b.fillRect(0, 0, 800, 600);
b.drawImage(start.getImage(),0,0,null);
b.dispose();
}
Notice that this calls paint() on the parent and dispose() on the graphics context when done. I just tried this code and it worked for me.

Drawing graphics on top of a JButton

I have a situation wherein I have a bunch of JButtons on a GridLayout. I need each of the JButtons to have:
a background image (but retain the ability to keep the default button look if needed)
custom graphics drawn on top by other classes
I have no trouble with the background image, since I am using setIcon() but I am having problems drawing things on top of the background. At one point I was able to draw on top of the button, but after the button was clicked, the drawings disappeared. How can make the button keep this drawing state?
Basically, I need a way for my JButtons to have public methods that would allow another class to draw anything on it such as:
public void drawSomething() {
Graphics g = this.getGraphics();
g.drawOval(3,2,2,2);
repaint();
}
or
public Graphics getGraphics() {
return this.getGraphics();
}
then another class could do this:
button.getGraphics().drawSomething();
The latter is more what I am looking for but the first is equally useful.
Is there any way to go about this? Also, overriding the parent class method paintComponent() doesn't help since I need each button to have different graphics.

you can subclass JButton and override paintComponent().
you can handle each button having a different graphic by providing an external 'painter' to the subclass. Or just have a different subclass for each different graphic.
public class MyButton extends JButton {
private Painter painter;
public void paintComponent(Graphics g) {
super.paintComponent(g);
painter.paint(g);
}
}
public interface Painter {
public void paint(Graphics g);
}
you cannot just paint on the button as you are doing as the painting will get lost when the button is next repainted.

You can create a BufferedImage and do custom painting on it and then draw the image in your custom paintComponent(...) method.
Look at the DrawOnImage example from Custom Painting Approaches.

Drawing graphics in java - NetBeans IDE

I created a new JApplet form in NetBeans:
public class UI extends javax.swing.JApplet {
//generated code...
}
And a JPanel in design mode named panou:
// Variables declaration - do not modify
private javax.swing.JPanel panou;
How do I get to draw a line on panou? I've been searching for this for 5 hours now so a code snippet and where to place it would be great. Using Graphics2D preferably.

Go to design mode
Right Click on the panel "panou"
Click "Costumize code"
In the dialog select in the first combobox "costum creation"
add after = new javax.swing.JPanel() this, so you see this:
 
panou = new javax.swing.JPanel(){
#Override
public void paintComponent(Graphics g)
{
super.paintComponent(g); // Do the original draw
g.drawLine(10, 10, 60, 60); // Write here your coordinates
}
};
Make sure you import java.awt.Graphics.
The line that you will see is always one pixel thick. You can make it more "line" by doing the following:
Create this method:
public static final void setAntiAliasing(Graphics g, boolean yesno)
{
Object obj = yesno ? RenderingHints.VALUE_ANTIALIAS_ON
: RenderingHints.VALUE_ANTIALIAS_OFF;
((Graphics2D) g).setRenderingHint(RenderingHints.KEY_ANTIALIASING, obj);
}
And add after super.paintComponent(g); (in your costum creation) this:
setAntiAlias(g, true);
Edit:
What you are doing wrong is: you paint the line once (by creating the frame).
When you paint the line the frame is also invisible. The first draw is happening when the frame becomes visible. The frame will be Repainted, so everything from the previous paint will disappear.
Always you resize the frame, everything will be repainted. So you have to make sure each time the panel is painted, the line also is painted.

To do custom painting in a JPanel, one would need to make a subclass of a JPanel, and then overload the paintComponent method:
class MyPanel extends JPanel {
public void paintComponent(Graphics g) {
// Perform custom painting here.
}
}
In the example above, the MyPanel class is a subclass of JPanel, which will perform whatever custom painting is written in the paintComponent method.
For more information on how to do custom painting in Swing components, Lesson: Performing Custom Painting from The Java Tutorials have some examples.
If one wants to do painting with Java2D (i.e. using Graphics2D) then one could do some painting on a BufferedImage first, then draw the contents of the BufferedImage onto the JPanel:
class MyPanel extends JPanel {
BufferedImage image;
public MyPanel() {
Graphics2D g = image.createGraphics();
// Do Java2D painting onto the BufferedImage.
}
public void paintComponent(Graphics g) {
// Draw the contents of the BufferedImage onto the panel.
g.drawImage(image, 0, 0, null);
}
}
Further reading:
Painting in AWT and Swing
Trail: 2D Graphics

Images and Panels

I'm having a problem adding a JPanel on top of an Image. This is what I'm trying to do:
Image bgImage = loadImage(filename);
JPanel jp = new JPanel();
jp.setBounds(100,100,100,100);
jp.setOpaque(true);
jp.setBackgroudColor(Color.red);
bgImage.add(jp);
After doing this, I only see the bgImage. I tried everything but I still can't show the panel. Can somebody help me?

You cannot place a component inside an Image. What you want to do is paint the Image onto the background of a swing component (like JPanel). All swing components have a paint() method that calls these three methods (perhaps not quite this order): paintComponent(), paintChildren(), paintBorder(). So, you want to override the paintComponent() method to paint your background image over the panel. When this runs, your custom method will be called, and then the paintChildren() method will be called, which will paint all "child" components over the top of your background image:
class BackgroundImagePanel extends JPanel {
public void setBackgroundImage(Image backgroundImage) {
this.backgroundImage = backgroundImage;
}
#Override
protected void paintComponent(Graphics graphics) {
super.paintComponent(graphics);
graphics.drawImage(backgroundImage, 0, 0, this);
}
private Image backgroundImage;
}
BackgroundImagePanel panel = new BackgroundImagePanel();
panel.setBackgroundImage(image);
panel.add(new JTextField("Enter text here..."));
panel.add(new JButton("Press Me"));

The "BackgroundImagePanel" solution paints the image at its actual size. If this is a requirement, then you can just use a JLabel instead of creating a custom component.
The BackgroundPanel entry shows how you can do this. It also provides a background panel with more custom image painting solutions, that will allow you to scale and tile the image, if this is part of your requirement.