iphone - How to adjust views using auto layout? -

i using autolayout in sample app. have 3 views, topview, middleview, bottomview.following constraint need,

topview:

1. always start @ x origin 10.
2. left , right margin 10.
3. height should vary based on screen bounds(or superview).

middleview:

1. there should 10 px vertical margin between top , middle view.
2. left , right margin 10.
3. height should vary based on screen bounds(or superview).

bottomview:

1. there should 10 px vertical margin between middle , bottom view.
2. left , right margin 10.
3. height should constant, 30.

i want based on device screen size, bottom view y origin should change middle , top view size adjust. problem here there no way find out, should y origin of bottom view , interface providing permanent constraint like:

1. top space superview middle view.
2. top space superview bottom view.

this because there no way find out height of views. difficulty determining height top , middle view.

you don't seem care height of top , middle view is, i'm going make decision you: have same height. add following contraints common superview of these 3 views (_topview,_middleview , _bottomview) subviews:

nsstring *vfl = @"v:|-(10)-[topview]-(10)-[middleview]-(10)-[bottomview(==30)]-(10)-|"; nsdictionary *dict = @{@"topview":_topview,@"middleview":_middleview,@"bottomview":_bottomview}; nsarray *a = [nslayoutconstraints                       constraintswithvisualformat: vfl                                          options: 0                                          metrics: nil                                            views: dict]; 

make sure align them horizontally well:

nsarray *b = [nslayoutconstraints             constraintswithvisualformat: @"h:|-(10)-[topview]-(10)-|"                                options: 0                                metrics: nil                                  views: dict]; nsarray *c = [nslayoutconstraints              constraintswithvisualformat: @"h:|-(10)-[middleview]-(10)-|"                                 options: 0                                 metrics: nil                                   views: dict]; nsarray *d = [nslayoutconstraints              constraintswithvisualformat: @"h:|-(10)-[bottomview]-(10)-|"                                 options: 0                                 metrics: nil                                   views: dict]; 

edit

the middle view label, say. labels have intrinsic content size. if don't set height of view, autolayout system know instinctively. (neat, right?) pinning top of _topview top of superview , bottom top of label, height should automatically calculated. have changed code reflect this.

edit 2

in order add constraints in code, find common ancestor (superview) of these 3 views , write [superview addconstraints:a],[superview addconstraints:b], etc... make sure autolayout in ib turned off , set translateresizingmaskstoconstraints no.