[Interest] Curious behaviour of slider/spin when controlled by keyboard

[Joseph Crowell]

I would suggest filing a bug report on this.

On 16/11/2012 3:58 AM, Shriramana Sharma wrote:
> Hello. I ran into a curious behaviour when writing a PyQt program but
> later found out that it is not particular to PyQt but exists in C++/Qt
> as well.
>
> I've attached minimal test cases. I note that in both the C++/PyQt
> minimal examples the bug is reproducible only when there is only a
> slider + a doubleSpin ("2-widgets") and not when there is also an
> integer spin ("3-widgets"). When there is an integer spin in addition
> ("3-widgets"), there is some lagging behind between the widgets (as
> can be seen visually as well as in the debug output) but it gets
> through and I'm able to run the whole range using the keyboard, but if
> there is no integer spin and only the double spin with the slider
> ("2-widgets") , the problem surfaces. It is clear this has something
> to do with the limitations of floating point data type (but I'm
> surprised it would surface even when only two decimal placesare
> involved).
>
> I presume others would have encountered such situations and would like
> advice on how to work around this limitation.
>
> The problem is as described below:
>
> Steps:
> 1. Let the focus be either on the slider or the spin. (The default
> slider/spin value is 0.50.)
> 3. Press up-arrow key to increase the slider/spin value.
>
> Observation:
> The value will not increase past 0.56.
>
> Steps:
> 4. Press down-arrow key to decrease the slider/spin value until 0.30.
> 5. Press down-arrow once more.
>
> Observation:
> The value jumps down from 0.30 to 0.28 even though the precision is set at 0.01.
>
> Step:
> 6. Press up-arrow.
>
> Observation:
> The value will now not rise above 0.28.
>
> Step:
> 7. Adjust the slider position using the mouse.
>
> Observation:
> The value can change to any value in its full range from 0.00 to 1.00.
>
> Step:
> 8. Adjust the slider using the mouse to go beyond 0.60.
> 9. Press down-arrow to decrease the value until 0.59.
> 10. Press down-arrow once more.
>
> Observation:
> 11. The value jumps down to 0.56.
> 12. It will no longer go above 0.56 using the keyboard (as before).
>
>
>
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