使用NSLayoutConstraint在Superview中使用UIPageControl进行编程垂直对齐

Question

到目前为止,我能够避免使用自动布局,因此(可能)愚蠢的问题道歉.

• 我有一个以编程方式构建的ViewController(例如,没有IB).
• 我有一个UIPageControl对象,它位于viewController视图的视图层次结构中(例如addSubview:)
• 相反,我需要将UIPageControl对象与UIViewController主视图的下边缘对齐.
• 我希望UIPageControl水平居中,但距离底部边缘20-40像素.

这里有一些示例代码,它创建UIPageControl并显示它,但根本不在正确的位置.

self.pageControl = [[UIPageControl alloc] init];
self.pageControl.numberOfPages = ...;
self.pageControl.otherAttributes = ...;
[self.view addSubview:[self pageControl]];

UIPageControl *pageControl = [self pageControl];
UIView *view = [self view];
NSDictionary *constaintDictionary = NSDictionaryOfVariableBindings(view, pageControl);


[self.view addConstraint:[NSLayoutConstraint constraintWithItem:pageControl
                                                     attribute:NSLayoutAttributeCenterX
                                                     relatedBy:NSLayoutRelationEqual
                                                        toItem:self.view
                                                     attribute:NSLayoutAttributeCenterX
                                                    multiplier:1
                                                      constant:0]];

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[pageControl]-20-[view]"
                                                                  options:0
                                                                  metrics:nil
                                                                    views:constaintDictionary]];

就像我说的,我对自动布局真的很陌生,所以我不确定我是否正确地实现了这些方法.

感谢您提前给予的帮助.

Answer 1

好吧,我想出了怎么做.花了很多时间,但在我再次阅读Visual Format Language文档后,我想出了这个:

UIPageControl *pageControl = [self pageControl];

[pageControl setTranslatesAutoresizingMaskIntoConstraints:NO];

[self.view addConstraints:[NSLayoutConstraint
                           constraintsWithVisualFormat:@"H:|-0-[pageControl]-0-|"
                           options:0
                           metrics:nil
                           views:NSDictionaryOfVariableBindings(pageControl)]];
[self.view addConstraints:[NSLayoutConstraint
                           constraintsWithVisualFormat:@"V:[pageControl]-40-|"
                           options:0
                           metrics:nil
                           views:NSDictionaryOfVariableBindings(pageControl)]];