Thread: I have a problem with slider in java swing

Hello,
I have a problem with slider which i want to create jlabels in a panel by sliding the slider and get the value but the jlabel doesn't show in jpanel.below is the code :

 JPanel PanelBoxes;
    JPanel panel;
    JLabel c; 
    public static void main(String[] args){
        DividePanel div = new DividePanel();
        div.go();
    }
 
    public void go(){
 
        JFrame frame = new JFrame("My Frame");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
        JSlider slide = new JSlider();
        slide.addChangeListener(new SlidersListener());
 
 
        JSlider slidev = new JSlider(JSlider.VERTICAL);
        //slidev.addChangeListener(new SlideListener());
 
        PanelBoxes  = new JPanel();
        PanelBoxes.setPreferredSize(new Dimension(200,150));
 
        panel = new JPanel();
        panel.setBorder(BorderFactory.createLineBorder(Color.RED,2,false));
        panel.add(BorderLayout.CENTER,PanelBoxes);
 
        frame.getContentPane().add(BorderLayout.NORTH,slide);
        frame.getContentPane().add(BorderLayout.WEST,slidev);
        frame.getContentPane().add(BorderLayout.EAST,new JPanel());
        frame.getContentPane().add(BorderLayout.SOUTH,new JPanel());
        frame.getContentPane().add(BorderLayout.CENTER,panel);
 
        frame.setSize(400, 300);
        frame.setVisible(true);
    }
 
    public class SlidersListener implements ChangeListener{
 
        @Override
        public void stateChanged(ChangeEvent e) {
            JSlider source = (JSlider) e.getSource();
 
            if(!source.getValueIsAdjusting()){
                int count=source.getValue();
                JOptionPane.showConfirmDialog(source,count);
                for(int i=0; i<2; i++){
                  c = new JLabel("asdasd");
                  c.setPreferredSize(new Dimension(100,30));
                  c.setBackground(Color.red);
                  c.setOpaque(true);
                  PanelBoxes.add(c);
                }
 
           }
        }

Thanks in advance guys

Adding components to a container "on the fly" isn't the recommended approach, but if you're set on it, then validate() the container after adding.

Originally Posted by GregBrannon

Adding components to a container "on the fly" isn't the recommended approach, but if you're set on it, then validate() the container after adding.

Can you explain me please how to do it with the right way?
I noticed that when i tried to resize the jframe the components appeared.

Can you explain better what the program is supposed to do? Right now, it adds 2 labels to panelBoxes each time a slider changes. I'm assuming that's a building block to where you'd like to go, so please explain the program's ultimate functionality. What is supposed to happen in response to changes in the the 2 slider values?

This looks like a work-in-progress code. The vertical slider doesn't do anything just yet as

//slidev.addChangeListener(new SlideListener());

is commented out.

Validate-ing the container is just that - a method call on the container on which the JLabels are being added. E.g.,

					c.setOpaque(true);
					PanelBoxes.add(c);
					PanelBoxes.revalidate();

Take a look at the API docs on the revalidate() method in JPanel (inherited from JComponent). Hth!

Originally Posted by GregBrannon

Can you explain better what the program is supposed to do? Right now, it adds 2 labels to panelBoxes each time a slider changes. I'm assuming that's a building block to where you'd like to go, so please explain the program's ultimate functionality. What is supposed to happen in response to changes in the the 2 slider values?

I want to divide equally a jpanel by creating random sub panel with the slider value. something like this Equivalent Fractions

public class DividePanel {
 
    JPanel PanelBoxes;
 
    public static void main(String[] args){
        DividePanel div = new DividePanel();
        div.go();
    }
 
    public void go(){
 
        JFrame frame = new JFrame("My Frame");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
        JSlider slide = new JSlider(1,4);
        slide.setValue(1);
        slide.setMajorTickSpacing(1);
        slide.setPaintTicks(true);
        slide.setPaintLabels(true);
        slide.setSnapToTicks(true);
        slide.addChangeListener(new SlidersListener());
 
        JSlider slidev = new JSlider(JSlider.VERTICAL);
        slidev.addChangeListener(new VerticalSliderListener());
 
        PanelBoxes = new JPanel();
        PanelBoxes.setPreferredSize(new Dimension(400,400));
        PanelBoxes.setBorder(BorderFactory.createLineBorder(Color.RED,2,false));
 
        frame.getContentPane().add(BorderLayout.NORTH,slide);
        frame.getContentPane().add(BorderLayout.WEST,slidev);
        frame.getContentPane().add(BorderLayout.EAST,new JPanel());
        frame.getContentPane().add(BorderLayout.SOUTH,new JPanel());
        frame.getContentPane().add(BorderLayout.CENTER,PanelBoxes);
        frame.validate();
 
        frame.setSize(500, 480);
        frame.setVisible(true);
    }
 
    public class SlidersListener implements ChangeListener{
 
        @Override
        public void stateChanged(ChangeEvent e) {
            PanelBoxes.removeAll();
            JSlider source = (JSlider) e.getSource();
 
            if(!source.getValueIsAdjusting()){
 
                int count=source.getValue();
                  //JOptionPane.showConfirmDialog(source,count);
                 for(int i=1; i<=count; i++){
                  JPanel b = new JPanel();
                  b.setPreferredSize(new Dimension(400,360/count));
                  b.setBackground(new Color((int)(Math.random()*256),(int)(Math.random()*256),(int)(Math.random()*256)));
                  b.setBorder(BorderFactory.createLineBorder(Color.RED, 1, false));
                  PanelBoxes.add(b);
                  PanelBoxes.validate();
                 }
               }
 
        }//end of state change 
    }//end of listener class

But again the window is not equally divided and i have minor spaces between jpanels.I want to make it better

I don't think you're really wanting to do anything 'randomly,' and adding JLabels to a component is not the same thing as dividing a component's area into grids.

Are you saying the slider along the left side indicates the number of rows the panel should have and the slider along the top indicates the number of columns? This effect can be accomplished rather simply by drawing equally spaced horizontal lines for the rows and vertical lines for the columns directly on the component's graphics object. You could check out the Java Tutorial Custom Painting to see how this is done.

Originally Posted by GregBrannon

I don't think you're really wanting to do anything 'randomly,' and adding JLabels to a component is not the same thing as dividing a component's area into grids.

Are you saying the slider along the left side indicates the number of rows the panel should have and the slider along the top indicates the number of columns? This effect can be accomplished rather simply by drawing equally spaced horizontal lines for the rows and vertical lines for the columns directly on the component's graphics object. You could check out the Java Tutorial Custom Painting to see how this is done.

Yes that i want to do! Can you suggest me links that can help me with that?

 MyDrawPanel panel;
    JFrame frame;
    int x = 0;
    int counter = 0;
    int stepping = 0;
    JSlider hslider;
    public static void main(String[] args){
        DividePanel div = new DividePanel();
        div.go();
    }
 
    public void go(){
 
        frame = new JFrame("My Frame");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
        hslider = new JSlider(1,4);
        hslider.setValue(1);
        hslider.setMajorTickSpacing(1);
        hslider.setPaintLabels(true);
        hslider.setPaintTicks(true);
        hslider.addChangeListener(new HsliderListener());
 
        panel = new MyDrawPanel();
        panel.setBorder(BorderFactory.createLineBorder(Color.BLUE,2,false));
 
        frame.getContentPane().add(BorderLayout.NORTH,hslider);
        frame.getContentPane().add(BorderLayout.CENTER,panel); 
 
        frame.setSize(400, 400);
        frame.setVisible(true);
 
    }
 
    public class MyDrawPanel extends JPanel{
 
        @Override
        public void paintComponent(Graphics g){
         g.setColor(Color.WHITE);
         g.fillRect(0, 0, this.getWidth(), this.getHeight());
 
         for(int i=1; i<counter; i++){
            stepping=400/counter;
            g.setColor(Color.BLUE);
            g.drawLine(0, x+stepping, this.getWidth(), x+stepping);
         }
 
        }
    }
      public class HsliderListener implements ChangeListener{
 
        @Override
        public void stateChanged(ChangeEvent e) {
            counter = hslider.getValue();
 
            panel.repaint();
        }
 
    }

I want to draw lines in jpanel so to be divided equally.but my code doesn't work correctly.When i drag the slider the slider is repaint in jpanel how is this possible???
Please can anyone help me

Java Custom Painting Lesson.

Originally Posted by GregBrannon

Java Custom Painting Lesson.

I have read the lessons but my problem remains can anyone help me with my code?My purpose is to divide a jpanel when i slide the slider.For example when i slide to 2 then divide the jpanel with a line to two.Helppppppp !!!

It's not clear how you applied what you 'learned' in the lesson to your project. Can you clarify?

Originally Posted by GregBrannon

It's not clear how you applied what you 'learned' in the lesson to your project. Can you clarify?

I have created a jframe, jpanel and jslider then i have add change listener on jslider so on change i save the value in variable and i have a for loop to draw n lines in jpanel.I have created a separate inner class which extends jpanel and i have method paintComponent which draw lines according to slider values on change.My problem is that i want to draw lines in jpanel so to be equally separated according to the values of jslider.If i am not clear,i can post the code.
Thanks mate

There is some simple math involved:

Read the row/column sliders
Determine the size of the drawing area
Divide the appropriate dimension of the drawing area into an equal number of rows/columns as specified by the sliders
Draw the row/column lines at the necessary intervals to show the desired number of rows/columns

Originally Posted by GregBrannon

There is some simple math involved:

Read the row/column sliders
Determine the size of the drawing area
Divide the appropriate dimension of the drawing area into an equal number of rows/columns as specified by the sliders
Draw the row/column lines at the necessary intervals to show the desired number of rows/columns

I divide the size of jpanel with the slider value, so if the user selects 2(counter) then stepping=400/counter and then with a for loop i want to draw lines each time +stepping

paint component(){
for(int i=0;i<counter;i++){
drawline(0, x+stepping,this.getwidth, x+stepping);
}
}
But the line does not appear.Can you help me with the code?

Are you meaning to use the paintComponent() method? Please properly post actual code, copied and pasted. Guessing at what you meant to post when typos are involved is just wasting time.

Also, verify the for loop actually does something. What is counter? Consider that for 2 rows, only one line is drawn. I think your current for loop would draw 2 lines for 2 rows (or columns).

Originally Posted by GregBrannon

Are you meaning to use the paintComponent() method? Please properly post actual code, copied and pasted. Guessing at what you meant to post when typos are involved is just wasting time.

Also, verify the for loop actually does something. What is counter? Consider that for 2 rows, only one line is drawn. I think your current for loop would draw 2 lines for 2 rows (or columns).

My task is very simple.Look Equivalent Fractions.I want to do that using java language.When i drag the slider to paint rows(or columns) in the white box.
First, i am not sure if my though is correct or not.When i drag the slider i get that value and save it in counter variable.Then i divide it with jpanel size e.g
400/counter if the counter=2 then 400/2=200 so draw a line g.drawline(0, 200,this.getwidth,200).So my jpanel will be divided to 2.

Below is my code and i am not sure if it's correct.

MyDrawPanel panel;
    JFrame frame;
    int counter = 0, x=0;
    int stepping = 0;
    JSlider hslider;
 
    public static void main(String[] args){
        DividePanel div = new DividePanel();
        div.go();
    }
 
    public void go(){
 
        frame = new JFrame("My Frame");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
        hslider = new JSlider(JSlider.HORIZONTAL,1,4,1);
        //hslider.setValue(1);
        hslider.setMajorTickSpacing(1);
        hslider.setPaintLabels(true);
        hslider.setPaintTicks(true);
        hslider.addChangeListener(new HsliderListener());
 
        frame.getContentPane().add(BorderLayout.SOUTH,hslider);
        frame.getContentPane().add(BorderLayout.CENTER,new MyDrawPanel()); 
 
        frame.setSize(400, 400);
        frame.setVisible(true);
 
    }
 
    public class MyDrawPanel extends JPanel{
 
        public MyDrawPanel(){
            setBorder(BorderFactory.createLineBorder(Color.BLUE,2, false));
        }
 
        @Override
        public Dimension getPreferredSize(){
            return new Dimension(400,400);
 
        }
        @Override
        public void paintComponent(Graphics g){
            super.paintComponent(g);
             g.setColor(Color.WHITE);
             g.fillRect(0, 0, this.getWidth(), this.getHeight());
 
             g.setColor(Color.BLUE);
             for(int i=0; i<counter; i++){
              x+=stepping;   
              g.drawLine(0, x, this.getWidth(), x);
             }
 
        }
    }
      public class HsliderListener implements ChangeListener{
 
        @Override
        public void stateChanged(ChangeEvent e) {
            counter = hslider.getValue();
            stepping = 400/counter;
            //JOptionPane.showConfirmDialog(rootPane, stepping);   
        }
    }

My task is to do the same as you see in the page i posted but with jframe and swing components.Sorry for wasting your time but i have spent hours with no solution.Tell me if i am not clear!!!

You made good progress and were almost there. You're getting frustrated. I made some minor changes with comments plus a few others I can't help making. (It's an OCD thing.) Let me know if you have any questions.

import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
 
public class DividePanel
{
    MyDrawPanel panel;
    JFrame frame;
    int counter = 0, x=0;
    int stepping = 0;
    JSlider hslider;
 
    public static void main(String[] args)
    {
        DividePanel div = new DividePanel();
        div.go();
    }
 
    public void go()
    {
        frame = new JFrame("My Frame");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
        hslider = new JSlider(JSlider.HORIZONTAL,1,4,1);
        //hslider.setValue(1);
        hslider.setMajorTickSpacing(1);
        hslider.setPaintLabels(true);
        hslider.setPaintTicks(true);
        hslider.addChangeListener(new HsliderListener());
 
        // create an instance of MyDrawPanel
        panel = new MyDrawPanel();
        frame.getContentPane().add(BorderLayout.SOUTH,hslider);
        // add the panel to the JFrame
        frame.getContentPane().add(BorderLayout.CENTER, panel ); 
 
        frame.setSize(400, 400);
        frame.setVisible(true);
 
    } // end method go()
 
    public class MyDrawPanel extends JPanel
    {
        // instance variables
        int columns;
 
        // default constructor
        public MyDrawPanel()
        {
            // initialize instance variables
            columns = 1;
            setBorder(BorderFactory.createLineBorder(Color.BLUE,2, false));
        }
 
        @Override
        public Dimension getPreferredSize(){
            return new Dimension(400,400);
        }
 
        @Override
        public void paintComponent(Graphics g)
        {
            super.paintComponent(g);
            g.setColor(Color.WHITE);
            g.fillRect(0, 0, this.getWidth(), this.getHeight());
 
            g.setColor(Color.BLUE);
 
            // draw equally spaced vertical lines for the number of columns
            int lines = columns - 1;
            int spacing = 0;
 
            if ( lines > 0 )
            {
                spacing = getWidth() / columns;
 
                // draw the lines
                for ( int i = 0 ; i <= lines ; i++ )
                {
                    g.drawLine( ( i * spacing ), 0, ( i * spacing ), getHeight() );
                }
            }
 
            // draw equally spaced horizontal lines for the number of rows
 
 
            // I'm not sure what this does
            for(int i=0; i<counter; i++)
            {
                x+=stepping;   
                g.drawLine(0, x, this.getWidth(), x);
            }
 
        }
 
        // to set the number of columns
        public void setColumns( int columns )
        {
            this.columns = columns;
        }
 
    } // end class MyDrawPanel
 
    public class HsliderListener implements ChangeListener
    {
        @Override
        public void stateChanged(ChangeEvent e)
        {
            counter = hslider.getValue();
            stepping = 400/counter;
 
            // use the panel instance to set the number of columns and
            // rows that should be drawn, then repaint
            panel.setColumns( counter );
            panel.repaint();
        }
 
    } // end class HsliderListener
 
} // end class DividePanel

Originally Posted by GregBrannon

You made good progress and were almost there. You're getting frustrated. I made some minor changes with comments plus a few others I can't help making. (It's an OCD thing.) Let me know if you have any questions.

import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
 
public class DividePanel
{
    MyDrawPanel panel;
    JFrame frame;
    int counter = 0, x=0;
    int stepping = 0;
    JSlider hslider;
 
    public static void main(String[] args)
    {
        DividePanel div = new DividePanel();
        div.go();
    }
 
    public void go()
    {
        frame = new JFrame("My Frame");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
        hslider = new JSlider(JSlider.HORIZONTAL,1,4,1);
        //hslider.setValue(1);
        hslider.setMajorTickSpacing(1);
        hslider.setPaintLabels(true);
        hslider.setPaintTicks(true);
        hslider.addChangeListener(new HsliderListener());
 
        // create an instance of MyDrawPanel
        panel = new MyDrawPanel();
        frame.getContentPane().add(BorderLayout.SOUTH,hslider);
        // add the panel to the JFrame
        frame.getContentPane().add(BorderLayout.CENTER, panel ); 
 
        frame.setSize(400, 400);
        frame.setVisible(true);
 
    } // end method go()
 
    public class MyDrawPanel extends JPanel
    {
        // instance variables
        int columns;
 
        // default constructor
        public MyDrawPanel()
        {
            // initialize instance variables
            columns = 1;
            setBorder(BorderFactory.createLineBorder(Color.BLUE,2, false));
        }
 
        @Override
        public Dimension getPreferredSize(){
            return new Dimension(400,400);
        }
 
        @Override
        public void paintComponent(Graphics g)
        {
            super.paintComponent(g);
            g.setColor(Color.WHITE);
            g.fillRect(0, 0, this.getWidth(), this.getHeight());
 
            g.setColor(Color.BLUE);
 
            // draw equally spaced vertical lines for the number of columns
            int lines = columns - 1;
            int spacing = 0;
 
            if ( lines > 0 )
            {
                spacing = getWidth() / columns;
 
                // draw the lines
                for ( int i = 0 ; i <= lines ; i++ )
                {
                    g.drawLine( ( i * spacing ), 0, ( i * spacing ), getHeight() );
                }
            }
 
            // draw equally spaced horizontal lines for the number of rows
 
 
            // I'm not sure what this does
            for(int i=0; i<counter; i++)
            {
                x+=stepping;   
                g.drawLine(0, x, this.getWidth(), x);
            }
 
        }
 
        // to set the number of columns
        public void setColumns( int columns )
        {
            this.columns = columns;
        }
 
    } // end class MyDrawPanel
 
    public class HsliderListener implements ChangeListener
    {
        @Override
        public void stateChanged(ChangeEvent e)
        {
            counter = hslider.getValue();
            stepping = 400/counter;
 
            // use the panel instance to set the number of columns and
            // rows that should be drawn, then repaint
            panel.setColumns( counter );
            panel.repaint();
        }
 
    } // end class HsliderListener
 
} // end class DividePanel

WOW Thanks so much , i was very close.How i will become so good as you? You read many books , hours of programming or it's a secret
How i will give you a thumps up for the help?

There's no secret sauce or handshake, Vulcan mind meld, or shortcut to acquiring the skills and confidence in using them. It's all practice, practice, and more practice. Reading the books doesn't help without applying what is read at a very high ratio of application to reading.

Keep coding, and you'll get there. No one can stop you. It's entirely up to you.