Home > Articles > Programming > Java

📄 Contents

  1. FAQ 319: What is eScript?
  2. FAQ 320: Language integration phase 1: How do I compile and build programs?
  3. FAQ 321: How do I load source files edited outside Eclipse?
  4. FAQ 322: How do I run an external builder on my source files?
  5. FAQ 323: How do I implement a compiler that runs inside Eclipse?
  6. FAQ 324: How do I react to changes in source files?
  7. FAQ 325: How do I implement an Eclipse builder?
  8. FAQ 326: Where are project build specifications stored?
  9. FAQ 327: How do I add a builder to a given project?
  10. FAQ 328: How do I implement an incremental project builder?
  11. FAQ 329: How do I handle setup problems for a given builder?
  12. FAQ 330: How do I make my compiler incremental?
  13. FAQ 331: Language integration phase 2: How do I implement a DOM?
  14. FAQ 332: How do I implement a DOM for my language?
  15. FAQ 333: How can I ensure that my model is scalable?
  16. FAQ 334: Language integration phase 3: How do I edit programs?
  17. FAQ 335: How do I write an editor for my own language?
  18. FAQ 336: How do I add Content Assist to my language editor?
  19. FAQ 337: How do I add hover support to my text editor?
  20. FAQ 338: How do I create problem markers for my compiler?
  21. FAQ 339: How do I implement Quick Fixes for my own language?
  22. FAQ 340: How do I support refactoring for my own language?
  23. FAQ 341: How do I create an Outline view for my own language editor?
  24. FAQ 342: Language integration phase 4: What are the finishing touches?
  25. FAQ 343: What wizards do I define for my own language?
  26. FAQ 344: When does my language need its own nature?
  27. FAQ 345: When does my language need its own perspective?
  28. FAQ 346: How do I add documentation and help for my own language?
  29. FAQ 347: How do I support source-level debugging for my own language?
  • Print
  • + Share This
This chapter is from the book

This chapter is from the book

FAQ 337: How do I add hover support to my text editor?

In FAQ 335 we describe how text hover is enabled for our editor through our configuration class:

class Configuration extends SourceViewerConfiguration {
   public ITextHover getTextHover(ISourceViewer sv,
    String contentType) {
      return new TextHover();

When the user moves the mouse over an area that corresponds to a given node in our AST, it is easy for us to provide a symbolic description of the node. Namely, the editor framework helps out by registering for the mouse events, setting timers, calling us at the right time, and drawing the box that will show the text hover. All that we need to do is match a certain location in the editor to a symbolic string. We do this by providing our own implementation of org.eclipse.jface.text.ITextHover as follows:

public class TextHover implements ITextHover {
   public IRegion getHoverRegion(ITextViewer tv, int off) {
      return new Region(off, 0);
   public String getHoverInfo(ITextViewer tv, IRegion r) {
      try {
         IDocument doc = tv.getDocument();
         EscriptModel em = EscriptModel.getModel(doc, null);
         return em.getElementAt(r.getOffset()).
      catch (Exception e) {
         return "";

The first method we implement is meant for optimizing the drawing of the text hover. We answer the question, If I am going to show a hover for character x in the text viewer, for what region should the hover be the same? We don’t try to be too smart here. We simply return an empty region.

The next method implements the real logic of the text hover. We convert the current cursor location to an AST element in the document and ask it to return a string relevant to the current context. Note that we assume that the EscriptModel implements a cache and that the getModel method is inexpensive as we will call it many times during editing.


FAQ 338 How do I create problem markers for my compiler?

  • + Share This
  • 🔖 Save To Your Account