Fl_Tree callback when FL_WHEN_RELEASE

Question

The documentation for Fl_Tree in FLTK 1.3.4 says:

The callback() is invoked depending on the value of when()

• FL_WHEN_RELEASE -- callback invoked when left mouse button is released on an item
• FL_WHEN_CHANGED -- callback invoked when left mouse changes selection state

but I can't get the callback called if the mouse is released and I can't see a difference between both. Any ideas?

#include <FL/Fl.H>
#include <FL/Fl_Double_Window.H>
#include <FL/Fl_Tree.H>

static void cb_(Fl_Tree*, void*)
{
  printf ("callback\n");
}

int main()
{
  Fl_Double_Window* w = new Fl_Double_Window(325, 325);
  Fl_Tree* o = new Fl_Tree(25, 25, 255, 245);
  o->callback((Fl_Callback*)cb_);
  o->when(FL_WHEN_RELEASE);
  o->add("foo/bar");
  o->add("foo/baz");
  o->end();
  w->show();
  return Fl::run();
}

this snippets outputs "callback" on every change, even if FL_WHEN_RELEASE is set.

Answer 1

If you have downloaded, the distribution, have a look at test/input.cxx and test/tree.cxx. Both have tests for the different when selections.

WHEN_CHANGED only makes sense on edit boxes, browsers and tables - you can verify the data as it is typed in. This does not happen with WHEN_RELEASE. For all other widgets, there is virtually no difference.

Edit

In order for release to fire every time, there are one of three options

1. Modify the source FL_Tree.cxx. Look for FL_Tree::select. Change alreadySelected to false.

2. If you look at the source, in the same routine, further down, it says

   #if FLTK_ABI_VERSION >= 10301
   

   If the library is built with FLTK_ABI_VERSION set to 10301, it will call the reselect but there is also a whole load of other stuff it will do when this #define is set since it affects all widgets

3. Comment out the #if FLTK_ABI_VERISON and corresponding #endif in FL_Tree::select.