[Qt-qml] ListView (optimization flags)

[Adriano Rezende]

On Sun, Feb 6, 2011 at 9:00 PM,  <martin.jones at nokia.com> wrote:
> We've done some preliminary experimentation with this, but it did not generally lead to an improvement because the case of item creation is optimized by delaying evaluation of bindings until component completion.
> Changing a number of bindings (i.e. roles) on existing items can result in bindings being evaluated multiple times which can be costly, especially for text layout.  There are probably delegates which would see improvement from this and it is something we will revisit in the future.

Probably the delegates I use fits in the last case, since the
performance difference is significant in those devices. But I'll port
the implementation to QML, so we can have a better comparison using
property bindings.

Regarding the number of binding evaluations, wouldn't be the same
number in both cases? For example, in the current implementation it
creates the delegate and evaluates the bindings in component
completion. In the recycle approach it wouldn't just evaluates the
same bindings without the creating the delegate?

> Reuse would also not work if the delegates store any state - there is no way to restore a delegate to its initial state.

Delegate states should be binded to model properties, otherwise the
state information would be lost after the delegate is destroyed. So,
it's possible to reset to the initial state, since the initial state
is dictated by the model data. But if you are talking about changing
the delegate without keeping persistence in the model, even in this
case a restoration is also possible using the clean signal and a
delegate code with well defined states.

Br,
Adriano