Below is an example of adding two panels to a frame. Only one panel (the 2nd, red panel) appears.
Why does the first panel disappear?
import java.awt.Color;
import javax.swing.*;
import javax.swing.border.EmptyBorder;
public class DisappearingPanelInFrame {
DisappearingPanelInFrame() {
JFrame f = new JFrame(this.getClass().getSimpleName());
f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
f.add(getColoredPanel(Color.GREEN));
f.add(getColoredPanel(Color.RED));
f.pack();
f.setVisible(true);
}
private JPanel getColoredPanel(Color color) {
JPanel p = new JPanel();
p.setBackground(color);
p.setBorder(new EmptyBorder(20, 150, 20, 150));
return p;
}
public static void main(String[] args) {
Runnable r = DisappearingPanelInFrame::new;
SwingUtilities.invokeLater(r);
}
}
The default layout of a JFrame (or more specifically in this case, the content pane of the frame) is a BorderLayout.
When adding a component to a BordeLayout with no constraint, the Swing API will put the component in the CENTER.
A BorderLayout can contain exactly one component in each of the 5 layout constraints.
When a second component is added to the same (in this case CENTER) constraint of a BorderLayout, this implementation of Java will display the last component added.
As to what would be a better approach depends on the specific needs of the user interface.
When a second component is added to the same (in this case CENTER) constraint of a BorderLayout, this implementation of Java will display the last component added.
Not strictly true.
The BorderLayout will only reset the bounds (ie size and location) of the last component added to a specific constraint location. This is different from other layout managers in that they will reset the bounds of all components in the container.
In the example code the red panel was the "active" panel at the time the frame was validated by using the pack() method and therefore only its bound were set and therefore only it was painted.
For a demonstration of this process run the example below using the following steps:
Click on the "Add Panel in Center" button, nothing appears to happen even though the blue panel was added to the center.
Move the mouse over the red panel and the buttons will appear because the mouse rollover logic will cause the buttons to be repainted.
Now increase the frame width and the blue panel will appear under the red panel.
The code:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.EmptyBorder;
public class DisappearingPanelInFrame {
DisappearingPanelInFrame()
{
JButton button = new JButton ("Add Panel In Center");
button.addActionListener( new ActionListener()
{
#Override
public void actionPerformed(ActionEvent e)
{
JPanel blue = new JPanel();
blue.setBackground( Color.BLUE );
blue.add( new JButton("Button 1") );
blue.add( new JButton("Button 2") );
Component c = (Component)e.getSource();
Window window = SwingUtilities.windowForComponent(c);
window.add(blue );
window.revalidate();
window.repaint();
}
});
JFrame f = new JFrame(this.getClass().getSimpleName());
f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
f.add(new ColoredPanel(Color.GREEN));
//f.pack();
f.add(new ColoredPanel(Color.RED));
f.add(button, BorderLayout.SOUTH);
f.pack();
f.setVisible(true);
}
public static void main(String[] args) {
Runnable r = new Runnable() {
#Override
public void run() {
new DisappearingPanelInFrame();
}
};
SwingUtilities.invokeLater(r);
}
}
class ColoredPanel extends JPanel {
ColoredPanel(Color color) {
setBackground(color);
setBorder(new EmptyBorder(20, 150, 20, 150));
}
}
When the blue panel is added to the BorderLayout and when the revalidate() is invoked the bounds of the blue panel are set.
However, because of the way Swing does ZOrder painting the blue panel is painted first and then the red panel is painted on top of the blue panel. The green panel still has a size of (0, 0) since it was never the "active" panel in the BorderLayout.CENTER when the frame was initially validated with the pack() method.
When the frame is resized, the blue panel being the "active" panel in the BorderLayout.CENTER, has its bounds adjusted, so it will now fill the extra space in the frame.
Now for another test:
pack() the frame after adding the green panel to the frame.
run the code and increase the width of the frame and the red and green frame will appear
then click the button and increase the width and now all 3 panels will appear
Bottom line is still the same:
Don't try to add multiple panels to the same constraint of a BorderLayout. If you do, then make sure you remove the previous panel or you have the potential for unexpected results.
Related
So basically when I add a button it essentially pushes the black rectangle drawn in this program down, putting it out of its given location. How would you fix this?
import javax.swing.*;
import java.awt.*;
public class Grid {
public class homeGraphics extends JComponent {
homeGraphics() {
setPreferredSize(new Dimension(450, 600));
}
public void paint(Graphics g) {
super.paint(g);
g.fillRect(200, 275, 50, 50);
}
}
public void homeFrame() {
JFrame frame1 = new JFrame();
frame1.setSize(450, 600);
frame1.setResizable(false);
frame1.setDefaultCloseOperation(frame1.EXIT_ON_CLOSE);
JButton playButton = new JButton("Play");
playButton.setPreferredSize(new Dimension(60, 30));
JPanel panel1 = new JPanel();
panel1.add(playButton);
panel1.add(new homeGraphics());
frame1.add(panel1);
frame1.setVisible(true);
}
public static void main(String args[]) {
Grid frame = new Grid();
frame.homeFrame();
}
}```
it essentially pushes the black rectangle drawn in this program down, putting it out of its given location.
What do you mean out of its location? Painting is always done relative to the component. So your painting will always be done at (200, 275) of the component.
If you are attempting to paint at (200, 275) relative to the "frame", then don't. That is NOT how painting works.
Other problems with your code:
Don't attempt to set the size of your frame. If the custom panel is (450, 600) how can the frame possibly be the same size? The frame also contains the "title bar" and "borders". Instead of using setSize(), you invoke frame.pack()just beforeframe1.setVisible(….)`.
Class names start with an upper case character. Learn by example. Have you ever seen a class name in the JDK that doesn't start with an upper case character?
Custom painting is done by overriding paintComponent(…), not paint().
By default a JPanel uses a FlowLayout. So what you see it the button on one line and then the "HomeGraphics" class is too big to fit on the same line so it wraps the to the second line.
You should be more explicit when you do frame layout. So your code should be something like:
JPanel wrapper = new JPanel();
wrapper.add( playButton );
//JPanel panel1 = new JPanel();
//panel1.add(playButton);
//panel1.add(new homeGraphics());
JPanel panel1 = new JPanel( new BorderLayout() );
panel1.add(wrapper, BorderLayout.PAGE_START);
panel1.add(new HomeGraphics(), BorderLayout.CENTER);
Now the code shows your layout attempt more clearly.
I have a JFrame, which contains just a JPanel.
I add an mouse event to the JPanel.
But the whole JFrame gets the same mouse event.
Here is my code:
public class TestSwing extends JPanel {
public TestSwing() {
super.setSize(20, 20);
addMouseListener(new MouseAdapter() {
public void mousePressed(MouseEvent me) {
System.out.println(me);
}
});
}
public static void main(String[] args) {
JFrame frame = new JFrame();
frame.getContentPane().add(new TestSwing());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(200, 200);
frame.setVisible(true);
}
}
I set the size of the JPanel (20, 20), but no matter where I click, the mouse event will always be triggered.
You're adding that JPanel to the JFrame's contentPane, a component that uses BorderLayout, a layout which does not respect size or even for the most part preferred size, and so the JPanel will fill the entire JFrame's contentPane. Give the contentPane a FlowLayout and set the JPanel's preferred size and you'll see a difference. In the future, give the JPanel a Border to see its boundaries. This will make debugging this easy.
If you don't tell it otherwise, your JFrame will have BorderLayout like this:
Now if you furthermore don't tell your Panel where to go, it wil go into CENTER and thus be resized to fill whole content area.
For checking MouseEvent on only one JPanel I suggest you add another JPanel (maybe with different background?) to other area:
frame.getContentPane().add(new TestSwing(), BorderLayout.CENTER);
JPanel left = new JPanel();
left.setBackground(Color.red);
frame.getContentPane().add(left, BorderLayout.LEFT);
Size set by setSize() is only valid until it's recalculated based on Layout and other properties.
Don't know if I'm making a rookie mistake, but changing the row parameter when creating a GridLayout for a JPanel in my JFrame, seems to be causing another JPanel to vanish altogether:
Here's the stripped down version of the code:
In the GridBug constructor I set up my layout and put a sub class of JPanel in BorderLayout.CENTER. This does other stuff in my original code, but here just draws a box to show it's being displayed.
Somehow the state of the bottom panel which is added to BorderLayout.PAGE_END causes the center panel to vanish
In particular, changing the GridLayout row parameters to a higher value causes the center panel to vanish, lower values work fine
The code as it is now, does not work on my computer, if I uncomment some of the code to reduce row parameters, or if I don't add the JLabel or subPanels then it works...
I have no idea what I'm doing wrong:
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.GridLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class GridBug extends JFrame{
static class ImagePanel extends JPanel{
#Override
public Dimension getPreferredSize(){
return new Dimension(200,200);
}
#Override
public void paintComponent(Graphics g){
super.paintComponent(g);
System.out.println("Painting image panel...");
g.setColor(Color.CYAN);
g.fillRect(0, 0, getWidth(), getHeight());
}
}
public GridBug() {
setLayout(new BorderLayout());
/*PROBLEM CODE HERE*/
//add center image panel - does not appear depending on GridLayout settings in other panels
ImagePanel centerPanel = new ImagePanel();
add(centerPanel , BorderLayout.CENTER);
//add bottom panel
JPanel bottomPanel = new JPanel();
add(bottomPanel, BorderLayout.PAGE_END);
bottomPanel.setLayout(new GridLayout(6,0)); //doesn't work
// bottomPanel.setLayout(new GridLayout(5,0)); //works
JPanel subPanel = new JPanel();
//if I pass more than 4 or so rows as param to gridlayout,
//then imagePanel is not displayed
subPanel.setLayout(new GridLayout(4,0)); //doesn't work
// subPanel.setLayout(new GridLayout(3, 0)); //works
//if I don't add this label - works
JLabel label = new JLabel("A Label:");
subPanel.add(label);
bottomPanel.add(subPanel); //if I don't add the subPanel it works fine
/*END OF PROBLEM CODE?*/
//set window params
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(400,400);
setLocationRelativeTo(null);
setVisible(true);
}
public static final void main(String[] args){
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new GridBug();
}
});
}
}
Not sure the exact result you want, so I didn't even try. But the problem you're facing, is one of the reasons, you want to pack() your frame, and not setSize(). You're constricting the preferred sizes of the component. pack() respects the preferred size of all your components, and should be used, rather than setSize()
bottomPanel.setLayout(new GridLayout(6,0)); //doesn't work..
// with pack(), now it does.
pack();
//setSize(400,400); // if you increase the size it'll work also, but just pack()
You just need to work on the laying out of your components now to get your desired look :)
A more detailed explanation of your problem.
This is how you code currently looks when I set the background. Note: you can already see the setSize() is taking a toll on your top panel's preferred size (200, 200).
The top CYAN is your image panel.
The BLUE is the subPanel with 4 row. With GridLayout, all the rows will be at least the size of it largest component. In this case it's the label. You can see the blue area is 4 times the height of the label (as it should be)
Not the RED, which is the bottomPanel. This has 5 rows. The largest component is the subPanel, so the total size of the bottomPanel is the size of the subPanel x 5, as you can also see. Once you add another row, the top panel gets pushed out.
What kind of layout should I use to create a page Like this:
It should be resizable
It has two main panels Right and Left?
Extra space will be given to the 'Main Text' text area, and extra height will be given to the button panel while centering them.
import java.awt.*;
import javax.swing.*;
import javax.swing.border.EmptyBorder;
public class EndOfLineButtonLayout {
public static void main(String[] args) {
Runnable r = new Runnable() {
#Override
public void run() {
// the GUI as seen by the user (without frame)
JPanel gui = new JPanel(new BorderLayout());
gui.setBorder(new EmptyBorder(2, 3, 2, 3));
JPanel textPanel = new JPanel(new BorderLayout(5,5));
textPanel.add(new JScrollPane(new JTextArea("Top Text",3,20)),
BorderLayout.PAGE_START);
textPanel.add(new JScrollPane(new JTextArea("Main Text",10,10)));
gui.add(textPanel, BorderLayout.CENTER);
JPanel buttonCenter = new JPanel(new GridBagLayout());
buttonCenter.setBorder(new EmptyBorder(5,5,5,5));
JPanel buttonPanel = new JPanel(new GridLayout(0,1,5,5));
for (int ii=1; ii<6; ii++) {
buttonPanel.add(new JButton("Button " + ii));
}
// a component added to a GBL with no constraint will be centered
buttonCenter.add(buttonPanel);
gui.add(buttonCenter, BorderLayout.LINE_END);
JFrame f = new JFrame("Demo");
f.add(gui);
// Ensures JVM closes after frame(s) closed and
// all non-daemon threads are finished
f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
// See http://stackoverflow.com/a/7143398/418556 for demo.
f.setLocationByPlatform(true);
// ensures the frame is the minimum size it needs to be
// in order display the components within it
f.pack();
// should be done last, to avoid flickering, moving,
// resizing artifacts.
f.setVisible(true);
}
};
// Swing GUIs should be created and updated on the EDT
// http://docs.oracle.com/javase/tutorial/uiswing/concurrency/initial.html
SwingUtilities.invokeLater(r);
}
}
You can use gridbag layout, try using netbeans, I have tried it and found really usefull.
Once you create it with netbeans you can use the same and build infact any kind of layout.
best of luck with other solutions.
p.s. border layout is perfect for your requirement, but I mentioned this just in case you would like to do lot more .
I would use BorderLayout.
Create Three JPanels and add them to a JFrame as follows:
public class YourClass extends JFrame{
//code here
this.setLayout(new BorderLayout());
this.add(TopPanel, BorderLayout.NORTH);
this.add(RightPanel, BorderLayout.EAST);
this.add(MainPanel, BorderLayout.CENTER);
this.pack();
this.setVisible(true);
The two main panels would be placed inside a main JPanel using a BorderLayout. The left panel would be placed using BorderLayout.CENTER, and the right panel would be placed using BorderLayout.LINE_END.
The left panel would use a BoxLayout, Y axis to separate the two JPanels within the left panel.
The right buttons panel would use a GridBagLayout. This sizes the buttons the same and allows you to use Insets to add some spacing to the buttons.
The buttons would be spaced from the top to the bottom of the right buttons panel. If you want all the buttons towards the top of the right buttons panel, you would put the right buttons panel inside of another JPanel using a FlowLayout.
I have a JFrame, in this JFrame I have a JPanel that I draw on, this Panel can be any size and so I placed it into a JScrollpane to let me scroll when the panel is larger than the window screen size.
Unfortunately does not work as I expected:
Making the JFrame window smaller than the JPanel size does not show scroll bars
The JScrollPane size now seems locked to the size of the JPanel I have added to it, where as before it resized to the bounds of it's JFrame window (it still kinda does this but only vertically now?!)
The JPanel seems to assume the size of the JScrollpane regardless of what I set for preferred size
I am sure I'm doing something stupid, if someone could point out what I would be most grateful!
JPanel imageCanvas = new JPanel(); // 'Canvas' to draw on
JScrollPane scrollPane = new JScrollPane();
// set size of 'canvas'
imageCanvas.setMinimumSize(new Dimension(100,100));
// Scroll pane smaller then the size of the canvas so we should get scroll bars right?
scrollPane.setMinimumSize(new Dimension(50,50));
// Add a border to 'canvas'
imageCanvas.setBorder(BorderFactory.createLineBorder(new java.awt.Color(0, 0, 0)));
scrollPane.setViewportView(imageCanvas);
setPreferredSize() is the trick, setMinimumSize() and even setSize() on the component will be ignored by JScrollPane. Here's a working example using a red border.
import java.awt.*;
import javax.swing.*;
public class Scroller extends JFrame {
public Scroller() throws HeadlessException {
final JPanel panel = new JPanel();
panel.setBorder(BorderFactory.createLineBorder(Color.red));
panel.setPreferredSize(new Dimension(800, 600));
final JScrollPane scroll = new JScrollPane(panel);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setLayout(new BorderLayout());
add(scroll, BorderLayout.CENTER);
setSize(300, 300);
setVisible(true);
}
public static void main(final String[] args) throws Exception {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new Scroller().setVisible(true);
}
});
}
}
// suggest a size of 'canvas'
_ImageCanvas.setPreferredSize(new Dimension(100,100));
// Scroll pane smaller then the size of the canvas so we should get scroll bars right?
_ScrollPane.setPreferredSize(new Dimension(50,50));
// ..later
_Frame.pack();
Set preferred size on the canvas.
Increase dimensions 100,100 is too small atleast on my computer.
You may want to use new GridLayout(1,1); for you JFrame if you want the scrollpane to expand when you expand the frame.
As far as I remember there are 2 options:
define the preferredSize of _ImageCanvas
create a subclass of JPanel and implement Scrollable: http://docs.oracle.com/javase/7/docs/api/javax/swing/Scrollable.html
For more details, see the Javadoc:
http://docs.oracle.com/javase/7/docs/api/javax/swing/JScrollPane.html
Check out the Scrollable interface, this may help with the sizing issues.
These two method maybe helpful:
boolean getScrollableTracksViewportWidth();
boolean getScrollableTracksViewportHeight();