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POhow to handle bad file selection for image display in swing
 

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  1. POhow to handle bad file selection for image display in swing
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    <p>I am learning Swing and wrote an app that lets user select an image file and displays it on a <code>JPanel</code>. It works, but I want to handle situations when</p> <ol> <li>user doesn't select any file</li> <li>user selects a non image file</li> </ol> <p>In these cases I want to clear the <code>JPanel</code> and show an error message on a text area.</p> <p>I tried to do this as below.But I am not sure if this is the way to do this properly.I would like your suggestions.</p> <pre><code>import java.awt.*; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.image.BufferedImage; import java.io.File; import javax.imageio.ImageIO; import javax.swing.*; import javax.swing.filechooser.FileNameExtensionFilter; class Display extends JFrame { private MyImagePanel canvas; private JButton okbutton; private JTextArea result; private JFileChooser filechooser; private static Insets insets = new Insets(0, 0, 0, 0); public Display(String name) { super(name); this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); setLayout(new GridBagLayout()); addWidgets(); showGUI(); } private void showGUI() { this.pack(); this.setVisible(true); } private void addWidgets() { canvas = new MyImagePanel(); okbutton = new JButton("OK"); filechooser = new JFileChooser("Select imagefile"); FileNameExtensionFilter filter = new FileNameExtensionFilter( "Images", "jpg", "JPG", "GIF", "gif", "JPEG", "png", "PNG"); filechooser.setFileFilter(filter); filechooser.setControlButtonsAreShown(false); result = new JTextArea(10, 10); addComponent(filechooser, 0, 0, 2, 4, GridBagConstraints.CENTER, GridBagConstraints.NONE); addComponent(canvas, 2, 0, 2, 2, GridBagConstraints.CENTER, GridBagConstraints.NONE); addComponent(result, 2, 2, 2, 1, GridBagConstraints.CENTER, GridBagConstraints.NONE); addComponent(okbutton, 3, 3, 1, 1, GridBagConstraints.CENTER, GridBagConstraints.NONE); } public void addOKButtonListener(ActionListener okl) { okbutton.addActionListener(okl); } public void displayResult(String msg) { result.setText(msg); } public void clearResultField() { result.setText(""); } public void displayImage(String imagefilename) { canvas.setImage(imagefilename); } public String getSelectedFile() { java.io.File selectedFile = filechooser.getSelectedFile(); String filePathName = ""; if (selectedFile == null) { result.setText("select a file"); } else { filePathName = selectedFile.getPath(); } return filePathName; } public void addComponent(Component component, int gridx, int gridy, int gridwidth, int gridheight, int anchor, int fill) { GridBagConstraints gbc = new GridBagConstraints(gridx, gridy, gridwidth, gridheight, 1.0, 1.0, anchor, fill, insets, 0, 0); this.add(component, gbc); } }//end class Display class MyImagePanel extends JPanel { private BufferedImage bi; public MyImagePanel() { super(); bi = null; } public void setImage(String imagefilename) { try { bi = ImageIO.read(new File(imagefilename)); this.setPreferredSize(new Dimension(bi.getWidth(), bi.getHeight())); } catch (Exception e) { bi = null; } this.revalidate(); this.repaint(); } @Override public void paintComponent(Graphics g) { // clear the background g.setColor(getBackground()); g.fillRect(0, 0, getWidth(), getHeight()); if (bi != null) { // draw the image g.drawImage(bi, 0, 0, null); } } } class GUIController { private Display display; public GUIController(Display d) { display = d; display.addOKButtonListener(new OKButtonListener()); } class OKButtonListener implements ActionListener { public void actionPerformed(ActionEvent e) { display.clearResultField();//make result field blank String fileselection = display.getSelectedFile(); if (fileselection.length() &gt; 0) { display.displayImage(fileselection); } else { display.displayResult("actionPerformed:no file selected"); display.displayImage(""); } } } } public class ImageDisplay { public static void main(String[] args) { Display d = new Display("image demo"); GUIController ctrl = new GUIController(d); } } </code></pre>
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    1. COYes the file chooser appears, but there's no image. BTW, with an "@" address, no one but you will be notified of comments to your question.
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    2. CO@trashgod: thanks for the help..I copied the code from the above page and pasted it to a new file..It displays the image when selected through filechooser..I had to maximize the ui though..
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