Multi-tab editor

[fernandreu]

Main ideas:

• This would automatically implement #21
• Tabs would open when double-clicking an xml part, unlike now that they open on a single click
  • Collapsing the tree items of a part (i.e. its icons) should no longer happen on double click
• Automatic saving of tabs (JetBrains-style) or save on demand?
  • If saving each tab on demand, tool should distinguish between this and saving the entire document. What action should Ctrl-S do then? What should happen when you close the document or the application without saving? Should it ask you whether you want to save each tab individually?
  • Given there will be a proper undo history per tab, an automatic save seems like a better idea
• There could also be a tab for viewing an icon inserted, perhaps with pan / zoom controls and some file info (resolution, image format, file size, etc.)
• What to do with the results control (for find results / XML validation errors) at the bottom?
  • Keep having a single control common to all tabs: the control should be aware of which tab launched it, and have the ability to re-open it if it was already closed
  • Have an independent tab for each results control needed: this seems a bit of an overkill. Not even Visual Studio does that for find results
  • Keep one control per tab: this might be the easiest thing to do, with users clearly knowing which tab triggered the results (the one they are looking at)
• What should the tab title say?
  • If only showing the part name, you can easily end up with duplicates as soon as you open more than one document
  • If showing both file and part names, titles could be long
  • Intermediate approach, similarly to how IDEs resolve this:
    • When there is only one tab with that part name, show just that
    • When there is more than one, show also the file name
    • If there are still duplicates, show also the path
  • Also, check how viable it would be to highlight the part in the tree view that corresponds to the open tab
  • Maybe just temporarily, as soon as you have the focus on that tab
  • There could also be a find in tree view kind of manual action which would select the part there
• When a document is closed, the associated tabs should obviously close as well
• The selected item in the tree view should still be what decides which actions are available. This should be more intuitive than the currently focused editor deciding it
  • Actually, only for some actions such as inserting an icon. For purely code-related actions (validate XML, generate callbacks, etc.), it makes more sense if they are focused on the currently viewed tab

[fernandreu]

Fixed by #60. Some things might need to be polished but these can have their own issues.