Question

JDT and other plugins for Eclipse decorate the editor title image with problem status (compilation errors etc.). In my plugin I want to mimic that behaviour.

However, looking at the sources, JDT seems to do a lot of extra handling to do the decoration.

Decorators, especially lightweight ditto, is a handy way of doing decorations on icons, but I can find no way to programatically enable them for the title image of an editor. (And I don’t want to pull in all of JDT UI in my plugin…)

Is there such a way or do I need to implement my own ILabelProvider and then

public void updatedTitleImage(Image image) {
    setTitleImage(image);
}

like the JavaEditor does?

Answer 1

There seems to be no way to use decorators with the editor title image (as of 3.7 at least).

I ended up creating a EditorLabelUpdator which implemented the IResourceChangeListener interface (to find out when markers changed), basically the resourceChanged() method. It then uses a simple decorator-type class built from the pattern of OverlayImageIcon (of which you can find a lot of examples on Google).

The constructor is called from the initalization of the editor, sending the editor as a parameter which is saved for getting at the resource and its title icon.

The editor also had to be amended with a callback method triggering the title icon updating (updatedTitleImage(Image image)).

This is the core of the code I got:

public void resourceChanged(IResourceChangeEvent event) {
    if (isMarkerChangeForResource(event, editor)) {
        /* Changes in markers on this resource, so re-decorate title image */
        decorate();
    }
}

private boolean isMarkerChangeForResource(IResourceChangeEvent event, AlanEditor editor) {
    boolean isMarkerChangeForThisResource;
    final IResource resource = ResourceUtil.getResource(editor.getEditorInput());
    final IPath path = resource.getFullPath();
    IResourceDelta delta = event.getDelta().findMember(path);
    isMarkerChangeForThisResource = (delta != null) && ((delta.getFlags() & IResourceDelta.MARKERS) != 0);
    return isMarkerChangeForThisResource;
}

public void decorate() {
    Shell shell = editor.getEditorSite().getShell();
    if (shell != null && !shell.isDisposed()) {
        shell.getDisplay().syncExec(new Runnable() {
            public void run() {
                Image decoratedImage = decorateImage(editor.getTitleImage(), getSeverity());
                editor.updatedTitleImage(decoratedImage);
            }
        });
    }
}

private Image decorateImage(Image titleImage, int severity) {
    final ImageRegistry registry = AlanIDEPlugin.getDefault().getImageRegistry();
    String key = createKey(severity);
    ImageDescriptor descriptor = AlanIDEPlugin.getImageDescriptor(key);
    if (descriptor != null)
        return descriptor.createImage();

    OverlayImageDescriptor overlayImageDescriptor = buildDecoratedImage(severity, key);
    registry.put(key, overlayImageDescriptor);
    return overlayImageDescriptor.createImage();
}

private String createKey(int severity) {
    String key;
    switch (severity) {
    case IMarker.SEVERITY_ERROR: key = EDITOR_TITLE_ICON + ".error"; break;
    case IMarker.SEVERITY_WARNING: key = EDITOR_TITLE_ICON + ".warning"; break;
    default: key = EDITOR_TITLE_ICON; break;
    }
    return key;
}

private OverlayImageDescriptor buildDecoratedImage(int severity, String key) {
    ImageDescriptor overlay = null;
    if (severity >= IMarker.SEVERITY_ERROR)
        overlay = AlanIDEPlugin.getImageDescriptor("ovr16.error_ovr");
    else if (severity == IMarker.SEVERITY_WARNING)
        overlay = AlanIDEPlugin.getImageDescriptor("ovr16.warning_ovr");
    ImageDescriptor baseImage = AlanIDEPlugin.getImageDescriptor(EDITOR_TITLE_ICON);
    OverlayImageDescriptor overlayIcon = new OverlayImageDescriptor(baseImage);

    if (overlay != null)
        overlayIcon.addOverlay(overlay, IDecoration.BOTTOM_LEFT);
    return overlayIcon;
}

private int getSeverity() {
    int severity = 0;
    try {
        final IResource resource = ResourceUtil.getResource(editor.getEditorInput());
        severity = resource.findMaxProblemSeverity(IMarker.PROBLEM, true, IResource.DEPTH_INFINITE);
    } catch (CoreException e) {
        // Might be a project that is not open
    }
    return severity;
}

This was the simplest solution I could come up with.