Gutter

The Gutter class handles the Gutter component in the Code Editor component.

Gutter customization

Setting a Gutter handler

It is possible to customize the gutter, as for example:

• Add additional images or drawings in the gutter alongside the line numbers
• Show a Popup by right clicking on the gutter

This is achieved by implementing the GutterHandler interface.

For example:

   JEditor ta = new JEditor(defaults);
   ta.setGutterHandler(new TestGutterHandler());      

and:

   public class MyGutterHandler implements GutterHandler {
     private Image image = null;

     public MyGutterHandler() {
       URL url = thi.getClass().getResource("breakpoint.png");
       try {
         image = ImageIO.read(url);
       } catch (IOException ex) {
       }
     }

     @Override
     public boolean isPainting(int line) {
       // only the line of number 103 will have the image
       return line == 103;
     }

     @Override
     public boolean handleClick(Gutter gutter, int mouseButton, int x, int y) {
       JPopupMenu menu = new JPopupMenu();
       int number = gutter.getLineNumber(y);
       menu.add(new JMenuItem("An Action on " + number));
       menu.add(new JMenuItem("Another Action"));
       menu.show(gutter, x, y);
       return true;
     }

     @Override
     public void paint(Graphics gfx, int line, int x, int y) {
       gfx.drawImage(image, x - 16, y - 10, null);
     }
   }

We will have the following result:

Abstract Gutter handler

The AbstractGutterHandler is a GutterHandler which allows to:

• Show a specific image on specific lines
• Have a custom behavior upon clicking on the Gutter
• Have a custom behavior upon hovering on a line the gutter, such as for example showing a tooltip

For example, the following handler:

• Handles a right-click on the gutter and shows a menu for each line
• Shows a tooltip on lines which paint an image

For example:

   JEditor ta = new JEditor(defaults);
   MyGutterHandler handler = new MyGutterHandler();
   URL debugURL = ...
   handler.addImageResource("debug", debugURL);
   handler.addImage(103, "debug");
   ta.setGutterHandler(handler);      

and:

   private class MyGutterHandler extends AbstractGutterHandler {
     public boolean handleClick(Gutter gutter, int mouseButton, int x, int y) {
       if (mouseButton == MouseEvent.BUTTON3) {
         JPopupMenu menu = new JPopupMenu();
         int number = gutter.getLineNumber(y);
         menu.add(new JMenuItem("An Action on " + number));
         menu.show(gutter, x, y);
         return true;
       } else {
         return false;
       }
     }

     public void handleMoved(Gutter gutter, int x, int y) {
       int number = gutter.getLineNumber(y);
       if (isPainting(number)) {
         this.showTooltip("The tooltip on line" + number);
       } else {
         this.hideTooltip();
       }
     }
   }

Gutter default properties

Several CodeEditorDefaults properties allow to configure the gutter.