Autolayout自动布局3

    UIView *blueView = [[UIView alloc] init];    [self.view addSubview:blueView];    blueView.backgroundColor = [UIColor blueColor];    //不要将AutoresizingMask转为Autolayout的约束    blueView.translatesAutoresizingMaskIntoConstraints = NO;        UIView *redView = [[UIView alloc] init];    [self.view addSubview:redView];    redView.backgroundColor = [UIColor redColor];    //不要将AutoresizingMask转为Autolayout的约束    redView.translatesAutoresizingMaskIntoConstraints = NO;    /**************blueView的约束**************/    //添加高度约束：40    NSLayoutConstraint *heightConstraint = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:0.0 constant:40];    [blueView addConstraint:heightConstraint];        //添加左边约束：blueView的左边距离父控件右边有20的间距    NSLayoutConstraint *leftConstraint = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:blueView.superview attribute:NSLayoutAttributeLeft multiplier:1.0 constant:20];    [blueView.superview addConstraint:leftConstraint];        //添加右边约束：blueView的右边距离父控件右边有20的间距    NSLayoutConstraint *rightConstraint = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:blueView.superview attribute:NSLayoutAttributeRight multiplier:1.0 constant:-20];    [blueView.superview addConstraint:rightConstraint];        //添加顶部约束：blueView的顶部距离父控件的顶部有20的间距    NSLayoutConstraint *topConstraint = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:blueView.superview attribute:NSLayoutAttributeTop multiplier:1.0 constant:20];    [blueView.superview addConstraint:topConstraint];         /**************redView的约束**************/    //添加高度约束：跟blueView一致    NSLayoutConstraint *heightConstraint2 = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeHeight multiplier:1.0 constant:0];    [self.view addConstraint:heightConstraint2];        //添加左边约束：redView左边 == 父控件的中心X    NSLayoutConstraint *leftConstraint2 = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0];    [self.view addConstraint:leftConstraint2];        //添加顶部约束：redView的顶部距离blueView有20的间距    NSLayoutConstraint *topConstraint2 = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeBottom multiplier:1.0 constant:20];    [blueView.superview addConstraint:topConstraint2];        //添加右边约束：redView的右边 == blueView的右边    NSLayoutConstraint *rightConstraint2 = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeRight multiplier:1.0 constant:0];    [self.view addConstraint:rightConstraint2];