Delete a listbox item in OnDraw?

Question

I have a listbox and add items to it, items are address of files, items are added after some processes and they are inserted like this:

Listbox_Browser.Items := myItems;

so as im not adding them one by one i cant check them during inserting ti listbox, i tried to check them in OnDraw and used a code like this:

  Try
    FileOpenandP(Listbox_Browser.Items[Index]);
  Except
    ListBox_Browser.Items.Delete(Index);
  End;

but i got the error "List index out of bounds", what is the solution?

Answer 1

The OnDrawItem event is for drawing only. You are not supposed to be managing your list inside that event, only drawing its current items as needed.

Instead of assiging the whole list at one time, you should be checking the files first, then assign the remaining list to the ListBox, eg:

I := 0;
while I < myItems.Count do
begin
  try
    FileOpenandP(myItems[I]);
    Inc(I);
  except
    myItems.Delete(I);
  end;
end;
ListBox_Browser.Items := myItems;

If you don't want myItems altered, use a separate list instead:

tmpItems := TStringList.Create;
try
  tmpItems.Assign(myItems);
  I := 0;
  while I < tmpItems.Count do
  begin
    try
      FileOpenandP(tmpItems[I]);
      Inc(I);
    except
      tmpItems.Delete(I);
    end;
  end;
  ListBox_Browser.Items := tmpItems;
finally
  tmpItems.Free;
end;

Or:

ListBox_Browser.Items := myItems;
I := 0;
while I < ListBox_Browser.Items.Count do
begin
  try
    FileOpenandP(ListBox_Browser.Items[I]);
    Inc(I);
  except
    ListBox_Browser.Items.Delete(I);
  end;
end;

Or:

ListBox_Browser.Items.BeginUpdate;
try
  ListBox_Browser.Items.Clear;
  I := 0;
  for I := 0 to myItems.Count-1 do
  begin
    try
      FileOpenandP(myItems[I]);
    except
      Continue;
    end;
    ListBox_Browser.Items.Add(myItems[I]);
  end;
finally
  ListBox_Browser.Items.EndUpdate;
end;