ios - NSLayoutConstraint 将按钮放置在 View 的中心

Question

我正在尝试使用约束，它们看起来很不错:)

我想知道将按钮放置在 View 中心(水平和垂直)的 VisualString 是什么。

我应该使用

NSLayoutContraint(item: attribute: relatedBy: toItem: attribute: multiplier: constant)

Answer 1

与 Restraint你只需要这样做:

let imageViewHorizontalConstraint = NSLayoutConstraint(
  item:       imageView,
  attribute:  .CenterX,
  relatedBy:  .Equal,
  toItem:     self,
  attribute:  .CenterX,
  multiplier: 1.0,
  constant:   0
)

let imageViewVerticalConstraint = NSLayoutConstraint(
  item:       imageView,
  attribute:  .CenterY,
  relatedBy:  .Equal,
  toItem:     self,
  attribute:  .CenterY,
  multiplier: 1.0,
  constant:   0
)

addConstraints([imageViewHorizontalConstraint, imageViewVerticalConstraint])

没有视觉格式

 // Center horizontally
        [self addConstraint:[NSLayoutConstraint constraintWithItem:centerView
                                                         attribute:NSLayoutAttributeCenterX
                                                         relatedBy:NSLayoutRelationEqual
                                                            toItem:self
                                                         attribute:NSLayoutAttributeCenterX
                                                        multiplier:1.0
                                                          constant:0.0]];

        [self addConstraint:[NSLayoutConstraint constraintWithItem:centerView
                                                         attribute:NSLayoutAttributeCenterY
                                                         relatedBy:NSLayoutRelationEqual
                                                            toItem:self
                                                         attribute:NSLayoutAttributeCenterY
                                                        multiplier:1.0
                                                          constant:0.0]];

视觉格式

// Variables
NSDictionary *views = @{
                        @"view" : self.view,
                        @"superview" : self.view.superview,
                        };
NSDictionary *metrics = @{
                          @"width" : @(CGRectGetWidth(self.view.frame)),
                          @"height" : @(CGRectGetHeight(self.view.frame))
                          };

// Constraints
NSArray *constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[superview]-(<=1)-[view(width)]"
                                                               options:NSLayoutFormatAlignAllCenterY
                                                               metrics:metrics
                                                                 views:views];
[self.view.superview addConstraints:constraints];

constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[superview]-(<=1)-[view(height)]"
                                                      options:NSLayoutFormatAlignAllCenterX
                                                      metrics:metrics
                                                        views:views];
[self.view.superview addConstraints:constraints];