IOS自动布局

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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: