Re: Display image selected from JFileChooser

From:
Lew <noone@lewscanon.com>
Newsgroups:
comp.lang.java.programmer
Date:
Sat, 12 Jun 2010 08:38:10 -0400
Message-ID:
<huvv29$t2c$1@news.albasani.net>
On 06/12/2010 02:08 AM, jimmy wrote:

I am having big problems setting out my code and need help organising
it. I want to write a GUI that displays jpg images that are selected
by the user from a file chooser. I have written two classes: MyImage


Actually, three ...

does the painting to the screen and MyImageApp for drawing the button,
and then calls MyImage when it has returned an image selected by the
user. The problem is it doesn't work.


What does "doesn't work" mean? It hangs? It displays some different image?
It does nothing apparent? It gives errors?

Your request is like asking a doctor to prescribe medicine when all you'll
admit is, "I don't feel well". We need the specific symptoms, accurately
reported.

On the face of it, 'MyImage' refuses to use the image data passed to it.

I am almost there, but I think I am causing problems with MyImageApp.
I need to be able to access the BufferedImage returned by the
JFileChooser and pass it as an argument to MyImage for painting. I
just can't figure it out though. Can someone show me the errors of my
ways?


Stop using TAB to indent code for Usenet. Use up to four space characters per
indent level.

import ... [omitted for brevity]
    @SuppressWarnings("serial")
    class MyImage extends JPanel{

        private BufferedImage bi;

        public MyImage(BufferedImage imgSrc){

        int h = imgSrc.getHeight();

'NullPointerException' ("NPE") thrown here.

         int w = imgSrc.getWidth();

NPE here, but that the code doesn't get this far.

         bi = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
        }

        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.drawImage(bi, 0, 0, null);

'bi' will never have data.

         }
}

public class MyImageApp extends Component {
    BufferedImage image = null;

Here you set 'image' to 'null', twice.

     public void buildUI(){

        JButton button1 = new JButton("Open file");
        button1.setSize(150, 100);
        button1.addActionListener((ActionListener) new myevent());

By convention, class names should begin with an upper-case character and be in
camel case.

         final MyImage panny = new MyImage(image);

Here you build a 'MyImage' around a 'null' image, which in turn is ignored
except to throw 'NullPointerException'.

     }

    public static void main(String[] args){

GUI code should ONLY run on the Event Dispatch Thread (EDT).

     JFrame myFrame = new JFrame();

    myFrame.setTitle("Here's my Frame");
    myFrame.setSize(1000, 800);
    myFrame.setVisible(true);
    myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    MyImageApp core = new MyImageApp();
    core.buildUI();
    }
}

public class myevent implements ActionListener{


By convention, class names should begin with an upper-case character and be in
camel case.

     BufferedImage image;

This 'image' is disconnected from all proposed use of it. You never give it
to a component for display. It's also peculiarly scoped as an instance
variable of the event-handler class.

     public void actionPerformed (ActionEvent e){

        JFileChooser fileChooser = new JFileChooser();

        int returnVal = fileChooser.showOpenDialog(fileChooser);
        if (returnVal == JFileChooser.APPROVE_OPTION) {
            File file = fileChooser.getSelectedFile();
            System.out.println("Image selected: " + file.getPath());
        System.out.println("Image about to be loaded to buffer");

Don't use 'System.out.println()' for debugging. Don't even use
'System.err.println()'. This is especially bad for GUI code.

Use a logger.

             try {
            System.out.println("Image loaded to buffer");

            image = ImageIO.read(fileChooser.getSelectedFile());

Now what? You have the image, but you do nothing with it.

             System.out.println("Image stored as a buffered image");
        }
        catch (IOException ex) {
            System.out.println("problem accessing file
"+file.getAbsolutePath());
        }
    }
        else {
            System.out.println("File access cancelled by user.");
    }
    }
}


--
Lew

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