ios - AutoLayout programmatically cause issue in iphone 4 -

i learning auto layout code. learning purpose doing sample apps using autolayout. in sample app decided keep text field below 20 points top margin. here code

#import "sampleviewcontroller.h" @interface sampleviewcontroller (){ uitextfield *username; } @end @implementation sampleviewcontroller  - (void)viewdidload { [super viewdidload];  self.edgesforextendedlayout = uirectedgenone; [self prepareviews]; }  -(void)prepareviews{    username = [[uitextfield alloc]init];    username.placeholder = @"username";    [username setborderstyle:uitextborderstyleroundedrect];    username.translatesautoresizingmaskintoconstraints = no;     [self.view addsubview:username];    [self prepareconstraint]; } -(void)prepareconstraint{    nslayoutconstraint *constraint = [nslayoutconstraint                       constraintwithitem:username                       attribute:nslayoutattributecenterx                       relatedby:nslayoutrelationequal                       toitem:self.view                       attribute:nslayoutattributecenterx                       multiplier:1.0                       constant:0];     [self.view addconstraint:constraint];           constraint = [nslayoutconstraint                       constraintwithitem:username                       attribute:nslayoutattributewidth                       relatedby:nslayoutrelationequal                       toitem:nil                       attribute:nslayoutattributenotanattribute                       multiplier:1.0                       constant:250];     [self.view addconstraint:constraint];           constraint = [nslayoutconstraint                       constraintwithitem:username                       attribute:nslayoutattributetopmargin                       relatedby:nslayoutrelationequal                       toitem:self.view                       attribute:nslayoutattributetopmargin                       multiplier:1.0                       constant:20];     [self.view addconstraint:constraint];    }    @end 

when run code on iphone 4(ios 7.1) got output when run code on iphone 5s(ios 8.4) got output

guys don't know making mistake.kindly point out me making mistake.and got warning when run code on iphone 4 (ios 7.1) .

unable simultaneously satisfy constraints. @ least 1 of constraints in following list 1 don't want. try this: (1) @ each constraint , try figure out don't expect; (2) find code added unwanted constraint or constraints , fix it. (note: if you're seeing nsautoresizingmasklayoutconstraints don't understand, refer documentation uiview property translatesautoresizingmaskintoconstraints) ( "<nslayoutconstraint:0x14dcac70 h:|-(20)-[uitextfield:0x14d955b0] (names: '|':uiview:0x14d9b480 )>" )

will attempt recover breaking constraint <nslayoutconstraint:0x14dcac70 h:|-(20)-[uitextfield:0x14d955b0]
(names: '|':uiview:0x14d9b480 )>

break on objc_exception_throw catch in debugger. methods in uiconstraintbasedlayoutdebugging category on uiview listed in <uikit/uiview.h> may helpful.

this tested in 4s , 5s....you add width constraint view rather should apply textfield...

nslayoutconstraint *constraint = [nslayoutconstraint                                   constraintwithitem:username                                   attribute:nslayoutattributecenterx                                   relatedby:nslayoutrelationequal                                   toitem:self.view                                   attribute:nslayoutattributecenterx                                   multiplier:1.0                                   constant:0]; [self.view addconstraint:constraint];  constraint = [nslayoutconstraint               constraintwithitem:username               attribute:nslayoutattributewidth               relatedby:nslayoutrelationequal               toitem:nil               attribute:nslayoutattributenotanattribute               multiplier:1.0               constant:250]; [username addconstraint:constraint];  constraint = [nslayoutconstraint               constraintwithitem:username               attribute:nslayoutattributetopmargin               relatedby:nslayoutrelationequal               toitem:self.toplayoutguide               attribute:nslayoutattributebottom               multiplier:1.0               constant:20]; [self.view addconstraint:constraint];