在上一篇文章中我们简单的介绍了使用Visual Format Language创建布局约束来实现自动布局，这种方法创建的布局约束能够满足大部分的布局的需求。但是想要实现类似于这样的约束：button.width = 2 * button.height就不能满足要求了，这一篇我们我们简单介绍一下如何创建这样的布局约束。

Apple就是非常贴心，它为我们提供了另外一个方法创建类似于view1.attr1 = view2.attr2 * multiplier + constant这样的约束，方法如下：

 

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

下面我们用这种方法创建一个布局约束，实现一个按钮button的布局，button距离父视图的左侧60点，距离顶部30点，其中宽度W = 2 * H + 10。效果图如下

 

不多说，上代码

 

               - (void)viewDidLoad          {              [super viewDidLoad];              // Do any additional setup after loading the view.              self.edgesForExtendedLayout = UIRectEdgeNone;                            UIButton * button = [UIButton buttonWithType:UIButtonTypeSystem];              button.layer.borderColor = [UIColor blackColor].CGColor;              button.layer.borderWidth = 2.0;              [button setTitle:@"W=2*H" forState:UIControlStateNormal];              [self.view addSubview:button];                            [button setTranslatesAutoresizingMaskIntoConstraints:NO];                            NSMutableArray * tempConstraints = [NSMutableArray array];                            [tempConstraints addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-60-[button]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(button)]];              [tempConstraints addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-30-[button(==30)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(button)]];                            [self.view addConstraints:tempConstraints];                            [self.view addConstraint:[NSLayoutConstraint constraintWithItem:button attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:button attribute:NSLayoutAttributeHeight multiplier:2.0 constant:10.0]];          }         http://blog.csdn.net/dongbaojun_ios/article/details/12624393
- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    self.edgesForExtendedLayout = UIRectEdgeNone;

    UIButton * button = [UIButton buttonWithType:UIButtonTypeSystem];
    button.layer.borderColor = [UIColor blackColor].CGColor;
    button.layer.borderWidth = 2.0;
    [button setTitle:@"W=2*H" forState:UIControlStateNormal];
    [self.view addSubview:button];

    [button setTranslatesAutoresizingMaskIntoConstraints:NO];

    NSMutableArray * tempConstraints = [NSMutableArray array];

    [tempConstraints addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-60-[button]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(button)]];
    [tempConstraints addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-30-[button(==30)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(button)]];

    [self.view addConstraints:tempConstraints];

    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:button attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:button attribute:NSLayoutAttributeHeight multiplier:2.0 constant:10.0]];
}
http://blog.csdn.net/dongbaojun_ios/article/details/12624393