Hello,
I tried all examples for unity on my mobile phone, I found it is too hard to touch a sliderbar and there is no muti-touches(can only touch a control at the same time), no dragging scroll , no sliding TextBox, no going back or forward view. the examples on the github seems to be prepeared for PC games too, so I don't know how much work to do for mobile interaction experience?

Our default theme is not very mobile friendly. We are working on that. Almost all of our mobile clients are customizing their own theme adapted for each case. If you think you are missing an important feature for you, please report it in the tracker. We have a few tickets waiting to be solved. For example, right now default controls are not multi-touch aware. You need to extend them using touch events.