First off, it would be easier in this case to just set the switch as the accessoryView
of the cell and let it worry about the positioning.
The reason you're seeing a blurry image is that your switch's frame has its origin on a half-pixel. You're setting the center
of the switch, so where its origin is depends on the size of the switch (which is fixed, because UISwitch
always uses a system-defined size). So say the switch has a size of 79 x 27 (the standard size), setting the center's y-coordinate to 20 would cause the frame origin's y-coordinate to be at 6.5 (20.0 - 27.0 * 0.5).