ios - UIStackView: control of spacing -

i need have x number of buttons in horizontal uistackview, resides inside uiscrollview. requirement buttons should evenly distributed in stack view, , number of buttons increases should reduce spacings make them fit width of screen, there's minimum spacing, when spacing's reduced , reached minimum spacing, buttons can extend beyond width of screen.

for example, when have 3 buttons want layout them like

|b1 b2 b3|

when have 5 buttons (assume can still fit width of screen less spacing):

|b1 b2 b3 b4 b5|

but when have 6 buttons , have keep minimum spacing, want stack view scroll inside container uiscrollview.

looking @ doco of uistackview, property spacing is:

"the spacing property determines minimum spacing between arranged views."

so use minimum spacing requirement, first example have 3 items, guess need define stack view's size position, described in doco:

"define stack’s size along axis. in case, pin both edges of stack along it’s axis superview, defining stack view’s size in dimension. need pin 1 of other edges define stack view’s position. stack view sizes , positions content along axis fill defined space; however, unpinned edge moves freely, based on size of largest arranged view."

but problem is:

1. how layout 3 buttons, 1 @ left edge, 1 in middle , 1 @ right edge?
2. when have more items couldn't fit width of screen, how determine should not pin stack view's right edge right of superview, size can grow?

thanks!