Why my problem occured?

1) I’m changing the value of the object field that is used by SortField (projectInfo.name)
2) as a consequence - the sort order of sorted collection’s items changes
3) and then ‘getItemIndex’ cannot return correct value, returns -1 instead.

Thus, to conclude:

After changing the value of the object field that is used by SortField, we MUST call:
projects.refresh();

to resort the collection to enable ‘getItemIndex’ to return correct value.

var sortProjects : Sort = new Sort();
sortProjects.fields = [new SortField("name", true, false)];
projects.sort = sortProjects;
projects.refresh();

———————–
later in the code
———————–

var projectInfo : ProjectInfo = projects.getItemAt(1);
projectInfo.name = “New name”;
var index : int = projects.getItemIndex(projectInfo); // returns -1

That custom sort has a compare function set. The compare function didn’t handle the a==b element correctly.

Now, the ArrayCollection class will use your compare function when you call getItemIndex so it can do a quick binary search instead of a long linear search.

So using our bad sorting compare function, it never found anything equal, and you got that weirdness.