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Thread: Drawing in a JPanel

  1. #1
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    Question Drawing in a JPanel

    I want to make a drawing (A rectangle which is colored according RGB values that are scanned real-time), and add this drawing to a JPanel. This JPanel has to be added to the layout of the main frame. If I make a class which extends JPanel, and draw the rectangle in the paintComponent(Graphics g) method, the drawing isn't displayed.


  2. #2
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    Default Re: Drawing in a JPanel

    With no code I don't really know where to advise you, either post progress or take a look at this.

    THIS

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    Default Re: Drawing in a JPanel

    Here is my code:

    import java.awt.Container;
    import java.awt.GridBagConstraints;
    import java.awt.GridBagLayout;
    import java.awt.GridLayout;
    import java.awt.Insets;
     
    import javax.swing.*;
     
    public class Frame {
     
    	public static void main(String[] args) 
    	{
    		JFrame frame = new JFrame("gui");
    		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    		frame.setSize(500, 500);
     
    		Container pane = frame.getContentPane();
    		ColorValuesPanel values = new ColorValuesPanel();
     
    		GridBagLayout gridBagLayout = new GridBagLayout();
    		pane.setLayout(gridBagLayout);
    		GridBagConstraints c = new GridBagConstraints();
     
    		c.gridx = 0;
    		c.gridy = 0;
    		c.insets = new Insets(0, 0, 0, 0);
    		c.anchor = GridBagConstraints.WEST;
    		pane.add(values, c);
     
    		frame.setVisible(true);
    	}
    }

    import java.awt.Color;
    import java.awt.Graphics;
     
    import javax.swing.JPanel;
     
    public class ColorValuesPanel extends JPanel
    {
    	Color c;
    	int red = 50, green = 50, blue = 50;
     
    	public ColorValuesPanel()
    	{
    		super.setSize(500, 500);
    	}
     
    	protected void paintComponent(Graphics g)
    	{	
    		c = new Color(red, green, blue);
    		g.setColor(c);
    		g.fillRect(350, 50, 50, 400);
    	}
    }

    My problem is that the drawing isn't displayed. Without the gridbagLayout it works. But I need the gridbagLayout because this is part of a bigger GUI. It's like the size of the JPanel is set to (0, 0) even if I set the size of the ColorValuesPanel to (500, 500).

  4. #4
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    Default Re: Drawing in a JPanel

    Please use code tags when posting code, assistance can be found on the Announcements page.
    "Frame" is an existing class in Java, so using the name is discouraged. Perhaps use something like MyFrame or ProjectNameFrame, or what ever, but something not already being used in Java
    The accepted answer here will explain why setSize is not working as expected.
    Calling pack on the jframe will cause the layout manager(s) to adjust things according to the respective min max and preferred sizes, if they have been set...
    This page, as part of a larger tutorial series, explains more details and includes sample code using GridBagLayout

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    Stone (August 7th, 2013)

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    Default Re: Drawing in a JPanel

    Please wrap your code in the code tags to preserve formatting.

    A method to debug UI issues such as this is to add a border around the component, for instance in the constructor of the ColorValuesPanel
    setBorder(BorderFactory.createLineBorder(Color.RED));
    What this will do is add red border - this will at least let you see the size and placement of the component. From there you can alter the layouts, preferred size (hint, hint), call frame.pack() (hint, hint), etc... to see how they affect the size and placement of the Component.

  7. The Following User Says Thank You to copeg For This Useful Post:

    Stone (August 7th, 2013)

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    Default Re: Drawing in a JPanel

    Thank you, the setPreferredSize does work! I was using the setSize method at the JPanel but it didn't had any effect

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