To create a line or polygone feature, the user needs to click to the map to set a point. By double-clicking, the geometry can be accomplished to open the attribute widget. This behaviour is not appropriate for mobile devices since the double-click is not easy to accomplish both with fingers and pencils.
I suggest to place a button on the map or implement a different mechanism that can be easily used on mobile devices.
The same holds for removing a point on the line by right-click. This is not appropriate for mobile use.
