[Qt-interest] Model/View speed of Models with many many items and item changes

[Sean Harmer]

On Saturday 13 Jun 2009 09:47:21 Arnold Krille wrote:
> Hi,
>
> On Saturday 13 June 2009 01:09:04 RZ wrote:
> > But the block signals effect was quite overwhelming and sufficient - so
> > I stopped optimizing everything else ;-)
>
> As far as I know this means all the update signals are then send
> afterwards. Which mean after changing 10.000 data points, instead of a
> continuous stream of 10.000 dataChanged(index) signals, you will get them
> all after the signals are unblocked again. 
I don't think that this is true. Blocked signals just never get emitted 
(except for the destroyed() signal).

However, I agree that blocking signals from a model in this way is potentially 
not a good idea.

> But still these are 10.000
> signals. Which means after you pushed new data into the model for 1 second,
> the gui will slowly adopt to this for the next second. This might work when
> you only change lots of data for a short period, it is the wrong behaviour
> when changing lots of data continuously for hours (I have evaluations that
> run for several days non-stop; and really before I optimized it, I had the
> gui update for several hours to adopt to all the signals).
>
> And sadly Qt' doesn't allow combining of signals via a unified way, so you
> have to combine the dataChanged() signals somewhere in your code...
>
> For these specialized high-troughput use-cases you simply _have_ to
> implement your own models. Which isn't hard unless you want the special
> stuff like drag'n'drop... (/me has yet to extend a custom model to do
> drag'n'drop.)
Drag and drop is not difficult with custom models but there are a few 
necessary bits to it that can be tricky the first time you do it.

Sean