iOS auto layout

IOS Auto Layout

Introduction

Auto layout was introduced in iOS 6.0 and can only support IOS6.0 and higher. It helps us create interfaces for multiple devices.

Instance steps

1. Create a simple View based application

2. Modify the file content of ViewController.m as shown below

#import "ViewController.h"@interface ViewController ()@property (nonatomic, strong) UIButton *leftButton;@property (nonatomic, strong) UIButton *rightButton;@property (nonatomic, strong) UITextField *textfield;@end@implementation ViewController- (void)viewDidLoad{    [super viewDidLoad];    UIView *superview = self.view;    /*1. Create leftButton and add to our view*/    self.leftButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];    self.leftButton.translatesAutoresizingMaskIntoConstraints = NO;    [self.leftButton setTitle:@"LeftButton" forState:UIControlStateNormal];    [self.view addSubview:self.leftButton];    
    /* 2. Constraint to position LeftButton's X*/    NSLayoutConstraint *leftButtonXConstraint = [NSLayoutConstraint 
    constraintWithItem:self.leftButton attribute:NSLayoutAttributeCenterX 
    relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:superview attribute:    NSLayoutAttributeCenterX multiplier:1.0 constant:-60.0f];    /* 3. Constraint to position LeftButton's Y*/    NSLayoutConstraint *leftButtonYConstraint = [NSLayoutConstraint 
    constraintWithItem:self.leftButton attribute:NSLayoutAttributeCenterY 
    relatedBy:NSLayoutRelationEqual toItem:superview attribute:    NSLayoutAttributeCenterY multiplier:1.0f constant:0.0f];   
    /* 4. Add the constraints to button's superview*/    [superview addConstraints:@[ leftButtonXConstraint,
    leftButtonYConstraint]];    
    /*5. Create rightButton and add to our view*/    self.rightButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];    self.rightButton.translatesAutoresizingMaskIntoConstraints = NO;    [self.rightButton setTitle:@"RightButton" forState:UIControlStateNormal];    [self.view addSubview:self.rightButton];    
    /*6. Constraint to position RightButton's X*/    NSLayoutConstraint *rightButtonXConstraint = [NSLayoutConstraint 
    constraintWithItem:self.rightButton attribute:NSLayoutAttributeCenterX 
    relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:superview attribute:    NSLayoutAttributeCenterX multiplier:1.0 constant:60.0f];    /*7. Constraint to position RightButton's Y*/
    rightButtonXConstraint.priority = UILayoutPriorityDefaultHigh;    NSLayoutConstraint *centerYMyConstraint = [NSLayoutConstraint 
    constraintWithItem:self.rightButton attribute:NSLayoutAttributeCenterY 
    relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:superview attribute:    NSLayoutAttributeCenterY multiplier:1.0f constant:0.0f];    [superview addConstraints:@[centerYMyConstraint,
    rightButtonXConstraint]];   //8. Add Text field    self.textfield = [[UITextField alloc]initWithFrame:    CGRectMake(0, 100, 100, 30)];    self.textfield.borderStyle = UITextBorderStyleRoundedRect;    self.textfield.translatesAutoresizingMaskIntoConstraints = NO;    [self.view addSubview:self.textfield];    //9. Text field Constraints    NSLayoutConstraint *textFieldTopConstraint = [NSLayoutConstraint 
    constraintWithItem:self.textfield attribute:NSLayoutAttributeTop 
    relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:superview 
    attribute:NSLayoutAttributeTop multiplier:1.0 constant:60.0f];    NSLayoutConstraint *textFieldBottomConstraint = [NSLayoutConstraint 
    constraintWithItem:self.textfield attribute:NSLayoutAttributeTop 
    relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:self.rightButton 
    attribute:NSLayoutAttributeTop multiplier:0.8 constant:-60.0f];    NSLayoutConstraint *textFieldLeftConstraint = [NSLayoutConstraint 
    constraintWithItem:self.textfield attribute:NSLayoutAttributeLeft 
    relatedBy:NSLayoutRelationEqual toItem:superview attribute:    NSLayoutAttributeLeft multiplier:1.0 constant:30.0f];    NSLayoutConstraint *textFieldRightConstraint = [NSLayoutConstraint 
    constraintWithItem:self.textfield attribute:NSLayoutAttributeRight 
    relatedBy:NSLayoutRelationEqual toItem:superview attribute:    NSLayoutAttributeRight multiplier:1.0 constant:-30.0f];    [superview addConstraints:@[textFieldBottomConstraint ,
    textFieldLeftConstraint, textFieldRightConstraint, 
    textFieldTopConstraint]];   }- (void)didReceiveMemoryWarning{    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}@end