IOS自动布局

简介

自动布局在iOS 6.0中引入，仅可以支持IOS6.0 及 更高版本。它可以帮助我们创建用于多个种设备的界面。

实例步骤

1.创建一个简单的 View based application

2.修改 ViewController.m 的文件内容，如下所示

#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

输出

运行应用程序，在 iPhone 模拟器上会有下面的输出结果

当我们更改模拟器为横向的方向时，输出结果如下

我们在 iPhone 5 模拟器上运行同一应用程序时,输出结果如下

当我们更改模拟器为横向的方向时，输出结果如下: