Argument Out of Range issues using FMX TListBox - delphi

Question

I'm using a TListBox in Firemonkey, and I'm facing a strange issue when it comes to dynamically showing/hiding items. This includes both Delphi XE7 and XE8. The setup, there is a TPopupBox at the top of the form, where user chooses one of the items listed. Depending on which was chosen, the TListBox should show only certain TListBoxItems, and hide the rest. Part of this consists of resizing each list item height to 0 when not visible (otherwise it would leave an ugly gap between the items).
The problem is that very randomly and spontaneously (no pattern), selecting an item in this TPopupBox (calling OnChange which modifies visibility), produces an EArgumentOutOfRangeException at an unknown point. The code breaks in System.Generics.Collections.TListHelper.SetItemN() on the first line calling CheckItemRangeInline(AIndex); Within there, it's simply:
procedure TListHelper.CheckItemRangeInline(AIndex: Integer);
begin
if (AIndex < 0) or (AIndex >= FCount) then
raise EArgumentOutOfRangeException.CreateRes(#SArgumentOutOfRange);
end;
The exception continues to be raised over and over and over again with no end (starts with 4 in a row). When I use the debugger to step in, I can never manage to get it to happen.
There are a couple common procedures used here which control item visibility:
//lstTrans = TListBox
//Iterates through all items and hides everything
procedure TfrmMain.HideTransItems;
var
X: Integer;
begin
for X := 0 to lstTrans.Count-1 do begin
lstTrans.ListItems[X].Visible:= False;
end;
end;
//Sets height of visible items to 42, invisible items to 0
procedure TfrmMain.ResetTransHeights;
var
X: Integer;
LI: TListBoxItem;
begin
for X := 0 to lstTrans.Count-1 do begin
LI:= lstTrans.ListItems[X];
if LI.Visible then
LI.Height:= 42
else
LI.Height:= 0;
end;
end;
Then, when choosing something in the TPopupBox:
//cboTrans = TPopupBox
procedure TfrmMain.cboTransChange(Sender: TObject);
procedure E(AItem: TListBoxItem);
begin
AItem.Visible:= True;
end;
begin
HideTransItems; //Make all list items invisible
case cboTrans.ItemIndex of
0: begin
E(lbSomeListBoxItem);
E(lbSomeOtherItem);
//More calls to "E"
end;
1: begin
E(lbSomeListBoxItem2);
//More calls to "E"
end;
//More indexes
end;
ResetTransHeights; //Adjust visible list item heights to be seen
end;
(The full procedure is just a lot of the exact same types of calls, too much to post here)
Nowhere am I adding or removing items - only changing visibility
There are no events triggered which might be causing some faulty loop
The TPopupBox is located outside of the TListBox
Each TListBoxItem has one or two controls (yet it doesn't matter which ones are being shown/hidden)
Selecting an item in this TPopupBox may work one time, yet fail the next
Sometimes it occurs the first time I show/hide these items, sometimes it takes 20-30 tries
Never able to reproduce while stepping through in Debug
Why would I be receiving this exception, and how do I fix it?

Answer 1

Why would I be receiving this exception, and how do I fix it?
You know why you are receiving it. You are accessing an array with an index that lies outside the valid range.
The question is where that index is. If you cannot readily reproduce then you need to debug to gather diagnostics. On Windows you'd use a tool like madExcept to gather information. Most useful would be the call stack that led to the error.
If you don't have madExcept or a similar tool at hand use trace logging. Instrument your code so that it logs information that allows you to determine which access of the list is out of bounds. You'll likely end up iterating around this as you narrow down the search.
Finally, once you identify which code leads to the error, usually the problem becomes apparent.

Answer 2

I had the same issue when I was animating the height of a TListBoxItem.
The issue only occurred when I was changing the Height of a Selected item. I implemented Jerry Dodge's solution of setting the height to 0.01 instead of 0 which fixed the issue.
Delphi Berlin Code
{Delphi Berlin}
ItemIndex := 0;
Item := ListBox.ItemByIndex(ItemIndex);
Height := Item.Height;
FloatAnimation := TFloatAnimation.Create(nil);
FloatAnimation.Parent := Item;
FloatAnimation.PropertyName := 'height'
FloatAnimation.StartValue := Height;
FloatAnimation.StopValue := 0.01; {Setting to 0 causes "Argument out of range" if the item is selected}
FloatAnimation.Start;