在Java中使用滚动条更改颜色

Question

i want to change the background color of frame as per the value selected in 3 scrollbar? But it is not happening here is my code.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

class changeColor extends JFrame implements AdjustmentListener
{
    JScrollBar red;
    JScrollBar green;
    JScrollBar blue;


    changeColor()
    {
        super("SCROLLBAR DEMO");
        setLayout(new FlowLayout());
        setVisible(true);
        setSize(300,300);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        red=new JScrollBar(JScrollBar.HORIZONTAL);
        green=new JScrollBar(JScrollBar.HORIZONTAL);
        blue=new JScrollBar(JScrollBar.HORIZONTAL);
        add(red);
        add(green);
        add(blue);
        red.addAdjustmentListener(this);
        green.addAdjustmentListener(this);
        blue.addAdjustmentListener(this);   
    }

    public void adjustmentValueChanged(AdjustmentEvent ae)
    {
        int cr=0;
        int cg=0;
        int cb=0;
        if(ae.getSource()==red)
            cr=ae.getValue();
        else if(ae.getSource()==green)
            cg=ae.getValue();
        else if(ae.getSource()==blue)
            cb=ae.getValue();

        setBackground(new Color(cr,cg,cb)); 
    }


    public static void main(String args[])
    {
        changeColor obj=new changeColor();  
    }
}

The problem is that the background color is not changing. I want to know what is the problem and how can i fix it?

Answer 1

This is a good solution. First you are creating JFrame with it's normal methods such as setDefaultCloseOperation() , setBounds() , getContentPane() . Then create an object from your class then use that to call all the other methods through out the program, in this case I created object called app . One thing you have to keep in mind is that don't forget to use AdjustmentEvent e instead of ActionListener e :).

Also all the color changes must go with this panel.setBackground(new Color(sbar1.getValue(),sbar2.getValue(), sbar3.getValue() in AdjustmentEvent , because once the Scrollbar gets changed, it's value gets by the getValue() method and added to the new Color() method with in the setBackground() method.

    import javax.swing.*;  
    import java.awt.event.*;
    import java.awt.*;

    public class Main implements AdjustmentListener {

        private static void createAndShowGUI() {
            // make frame..
          JFrame frame = new JFrame("JScrollBar");
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          frame.setBounds(20,30,200,250);
          frame.getContentPane().setLayout(null);
          Main app = new Main();
          app.sbar1 = new JScrollBar(java.awt.Adjustable.VERTICAL, 127, 1,0,255);
          app.sbar1.setBounds(10,20, 10, 200);
          app.sbar1.setBackground(Color.red);
          app.sbar1.addAdjustmentListener(app);
          frame.getContentPane().add(app.sbar1);
          app.sbar2 = new JScrollBar(java.awt.Adjustable.VERTICAL, 127, 1,0,255);
          app.sbar2.setBounds(30,20, 10, 200);
          app.sbar2.setBackground(Color.green);
          app.sbar2.addAdjustmentListener(app);
          frame.getContentPane().add(app.sbar2);
          app.sbar3 = new JScrollBar(java.awt.Adjustable.VERTICAL, 127, 1,0,255);
          app.sbar3.setBounds(50,20, 10, 200);
          app.sbar3.setBackground(Color.blue);
          app.sbar3.addAdjustmentListener(app);
          frame.getContentPane().add(app.sbar3);

          app.panel = new JPanel();
          app.panel.setBounds(80,20,50,200);
          app.panel.setBackground(new Color(0,0,0));
          frame.getContentPane().add(app.panel);

          frame.setVisible(true); 
      }

      public void adjustmentValueChanged(AdjustmentEvent e)
      {
          panel.setBackground(new Color(sbar1.getValue(),sbar2.getValue(), sbar3.getValue()));
      }

      public static void main(String[] args) {
        // start off..
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
      }

      // application object fields    
      JScrollBar sbar1;
      JScrollBar sbar2;
      JScrollBar sbar3;
      JPanel panel;
}

I hope this helped you alot.!!!

Answer 2

I ran your code as you posted it and it sort of works, the background color does change.

Issue 1: The cr, cg, and cb need to be class variables. In this way, the colors from your selections will mix together. The way it is written, only one color will change at a time.

Issue 2: To get the full range of color, you will need to change your selections so that the range goes from 0 to 255. With the JScrollBar approach, I am only seeing values from 0 to 90. That could easily be fixed with a move to JSlider

Issue 3: You must set the color on the content pane of a JFrame. (See comment)

Comment: Java convention is to name classes with an uppercase, FYI.

Here is the change which may give the result you are looking for:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

class changeColor extends JFrame implements AdjustmentListener
{
    JScrollBar red;
    JScrollBar green;
    JScrollBar blue;
    int cr=0;
    int cg=0;
    int cb=0;


    changeColor()
    {
        super("SCROLLBAR DEMO");
        setLayout(new FlowLayout());
        setVisible(true);
        setSize(300,300);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        red=new JScrollBar(JScrollBar.HORIZONTAL);
        green=new JScrollBar(JScrollBar.HORIZONTAL);
        blue=new JScrollBar(JScrollBar.HORIZONTAL);
        add(red);
        add(green);
        add(blue);
        red.addAdjustmentListener(this);
        green.addAdjustmentListener(this);
        blue.addAdjustmentListener(this);   
    }

    public void adjustmentValueChanged(AdjustmentEvent ae)
    {

        if(ae.getSource()==red)
            cr=ae.getValue();
        else if(ae.getSource()==green)
            cg=ae.getValue();
        else if(ae.getSource()==blue)
            cb=ae.getValue();
        System.out.println(cr + ":" + cg + ":" + cb);

        // add color to content pane
        this.getContentPane().setBackground(new Color(cr,cg,cb)); 
    }


    public static void main(String args[])
    {
        changeColor obj=new changeColor();  
    }
}