动画将字符串添加到FireMonkey中的ListBox

Question

The following code nicely animates adding a new string to the end of a ListBox

procedure TForm6.AddItem(s: string);
var
  l : TListBoxItem;
  OldHeight : Single;
begin
  l := TListBoxItem.Create(Self);
  l.Text := s;
  OldHeight := l.Height;
  l.Height := 0;
  l.Parent := ListBox1;
  l.Opacity := 0;
  l.AnimateFloat('height', OldHeight, 0.5);
  l.AnimateFloat('Opacity', 1, 0.5);
end;

The item expands and fades in. However I want to be able to add the string into an arbitrary location in the ListBox - actually at the current ItemIndex. Does anyone know how to do this?

Answer 1

To work around the fact that ListBox1.InsertObject and ListBox1.Items.Insert don't work you can do the following

procedure TForm1.AddItem(s: string);
var
  l : TListBoxItem;
  OldHeight : Single;
  I: Integer;
  index : integer;
begin
  l := TListBoxItem.Create(nil);
  l.Text := s;
  OldHeight := l.Height;
  l.Height := 0;
  l.Opacity := 0;
  l.Index := 0;
  l.Parent := ListBox1;

  Index := Max(0, ListBox1.ItemIndex);
  for I := ListBox1.Count - 1 downto Index + 1 do
  begin
    ListBox1.Exchange(ListBox1.ItemByIndex(i), ListBox1.ItemByIndex(i-1));
  end;
  ListBox1.ItemIndex := Index;
  l.AnimateFloat('height', OldHeight, 0.5);
  l.AnimateFloat('Opacity', 1, 0.5);
end;

but is a bit ridiculous. It (eventually) adds the string in position 0 if there is no item selected, otherwise adds it before the selected item. This solution reminds me too much of Bubble Sort . You will need to add the math unit to your uses clause for the max function to work.

This does indeed seem to be a bug in FireMonkey (check Quality Central #102122 ), However I suspect a future FireMonkey update will fix this. If anyone can see a better way of doing this....

I've also made a movie about this for those who are interested, which illustrates things more clearly.

Answer 2

This should work, but it does nothing:

l := TListBoxItem.Create(ListBox1);
ListBox1.InsertObject(Max(ListBox1.ItemIndex, 0), l);

If I then call the following, I get an access violation:

ListBox1.Realign;

In fact, even this gives me an AV:

ListBox1.Items.Insert(0, 'hello');
ListBox1.Realign;

But this adds one, of course:

ListBox1.Items.Add('hello');

A bug perhaps?

Answer 3

Instead of

l.Parent := ListBox1;

use

ListBox1.InsertObject(Index, l);

where Index is the insertion position.

(Untested but from reading the sources it should work).