autolayout之nslayoutconstraint

+(instancetype)constraintWithItem:(id)view1
                        attribute:(NSLayoutAttribute)attr1
                        relatedBy:(NSLayoutRelation)relation
                           toItem:(id)view2
                        attribute:(NSLayoutAttribute)attr2
                       multiplier:(CGFloat)multiplier
                         constant:(CGFloat)c;

view1.attr1 = view2.attr2 * multiplier + c

UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 44, 44)];
    view.translatesAutoresizingMaskIntoConstraints = NO;
    view.backgroundColor = [UIColor redColor];
    [self.view addSubview:view];
    
    [self.view addConstraint:
     [NSLayoutConstraint constraintWithItem:view
                                  attribute:NSLayoutAttributeLeft
                                  relatedBy:NSLayoutRelationEqual
                                     toItem:self.view
                                  attribute:NSLayoutAttributeLeft
                                 multiplier:1
                                   constant:20]];
    
    [self.view addConstraint:
     [NSLayoutConstraint constraintWithItem:view
                                  attribute:NSLayoutAttributeTop
                                  relatedBy:NSLayoutRelationEqual
                                     toItem:self.view
                                  attribute:NSLayoutAttributeTop
                                 multiplier:1
                                   constant:30]];
    
    [self.view addConstraint:
     [NSLayoutConstraint constraintWithItem:view
                                  attribute:NSLayoutAttributeWidth
                                  relatedBy:NSLayoutRelationEqual
                                     toItem:self.view
                                  attribute:NSLayoutAttributeWidth
                                 multiplier:0
                                   constant:30]];
    
    [self.view addConstraint:
     [NSLayoutConstraint constraintWithItem:view
                                  attribute:NSLayoutAttributeHeight
                                  relatedBy:NSLayoutRelationEqual
                                     toItem:self.view
                                  attribute:NSLayoutAttributeHeight
                                 multiplier:0
                                   constant:30]];
    
    UIView *view1 = [[UIView alloc] init];
    view1.translatesAutoresizingMaskIntoConstraints = NO;
    view1.backgroundColor = [UIColor blueColor];
    [self.view addSubview:view1];
    
    
    [self.view addConstraint:
     [NSLayoutConstraint constraintWithItem:view1
                                  attribute:NSLayoutAttributeLeft
                                  relatedBy:NSLayoutRelationEqual
                                     toItem:view
                                  attribute:NSLayoutAttributeRight
                                 multiplier:1
                                   constant:20]];
    
    [self.view addConstraint:
     [NSLayoutConstraint constraintWithItem:view1
                                  attribute:NSLayoutAttributeTop
                                  relatedBy:NSLayoutRelationEqual
                                     toItem:view
                                  attribute:NSLayoutAttributeTop
                                 multiplier:1
                                   constant:0]];
    
    [self.view addConstraint:
     [NSLayoutConstraint constraintWithItem:view1
                                  attribute:NSLayoutAttributeWidth
                                  relatedBy:NSLayoutRelationEqual
                                     toItem:view
                                  attribute:NSLayoutAttributeWidth
                                 multiplier:1
                                   constant:0]];
    
    [self.view addConstraint:
     [NSLayoutConstraint constraintWithItem:view1
                                  attribute:NSLayoutAttributeHeight
                                  relatedBy:NSLayoutRelationEqual
                                     toItem:view
                                  attribute:NSLayoutAttributeHeight
                                 multiplier:1
                                   constant:0]];