I can not set slider thumb position

Hello. I can set slider thumb position only once when I lunch my app.
During using app it does not work.

I am trying to set thumb position outside (when Slider1.PositionChanged)
in different procedure. Can You help a little?

This works for me

Thank You. So my mistake.

When I use this (or may be next line):

I noticed that (when Slider1.PositionChanged) is working.
Is it some way to disable it for a while?

make a variable disabled when you disable it set the value of variable to true when you want enable set it's value to false now
when Slider positionChanged
if disabled you false
then //your code!

Not exactly understand but will be trying. Thanks.