iOS：Autolayout自动布局实例

#import "ViewController.h"

@interface ViewController ()
@property (strong,nonatomic)UIView *view1;
@property (strong,nonatomic)UIView *view2;
@end

    //创建view1
    self.view1 = [[UIView alloc]init];
    self.view1.backgroundColor = [UIColor redColor];
    self.view1.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:self.view1];
    
    //创建view2
    self.view2 = [[UIView alloc]init];
    self.view2.backgroundColor = [UIColor yellowColor];
    self.view2.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:self.view2];

    //view1的x坐标和父视图的x坐标的关系
    NSLayoutConstraint *LCLfet = [NSLayoutConstraint constraintWithItem:self.view1 attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeading multiplier:1.0 constant:20];

    //view1的y坐标和父视图的y坐标的关系
    NSLayoutConstraint *LCBottom = [NSLayoutConstraint constraintWithItem:self.view1 attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1.0 constant:-20];

    //view1和view2等宽
    NSLayoutConstraint *lcEqualWitdth = [NSLayoutConstraint constraintWithItem:self.view1 attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self.view2 attribute:NSLayoutAttributeWidth multiplier:1.0 constant:0];

    //view1和view2等高
    NSLayoutConstraint *lcEqualHeight = [NSLayoutConstraint constraintWithItem:self.view2 attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:self.view1 attribute:NSLayoutAttributeHeight multiplier:1.0 constant:0];

    //view2的x坐标和父视图的x坐标的关系
    NSLayoutConstraint *LCRight = [NSLayoutConstraint constraintWithItem:self.view2 attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTrailing multiplier:1.0 constant:-20];

    //view2的y坐标和父视图的y坐标的关系
    NSLayoutConstraint *LCBottom2 = [NSLayoutConstraint constraintWithItem:self.view2 attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1.0 constant:-20];

    //view1和view2的水平间距
     NSLayoutConstraint *lcGap = [NSLayoutConstraint constraintWithItem:self.view2 attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:self.view1 attribute:NSLayoutAttributeTrailing multiplier:1.0 constant:20];

    //在父视图中添加约束
    [self.view addConstraints:@[LCLfet,LCBottom,LCRight,LCBottom2,lcEqualHeight,lcEqualWitdth,lcGap]];

    //view1固定的高度
    NSLayoutConstraint *lcFixedHeight = [NSLayoutConstraint constraintWithItem:self.view1 attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeHeight multiplier:1.0 constant:200];

    //在view1上添加约束
    [self.view1 addConstraint:lcFixedHeight];