ios - Objective-C - 在屏幕中间画一条水平线

Question

我正在尝试在具有导航栏的应用程序的屏幕中间绘制一条水平线。这是我当前的代码:

CGFloat screenWidth = self.view.frame.size.width;
CGFloat screenHeight = self.view.frame.size.height;
CGFloat navigationBarHeight = self.navigationController.navigationBar.frame.size.height;
CGFloat lineThickness = 3;

UIView *horizontalLine = [[UIView alloc] initWithFrame:CGRectMake(0, (screenHeight - navigationBarHeight) / 2, screenWidth, lineThickness)];
[self.view addSubview:horizontalLine];

我使用了非常相似的计算来绘制一条垂直线 - 并且效果很好。但是，问题是，无论使用什么设备，这条水平线在屏幕上的位置都太低了大约 10 个像素。我可能缺少偏移量吗？也许与导航栏有关？

Answer 1

好吧，我先这样做了..但它没有居中。但它应该是! :) 在此之下，我将其更改为添加一个 View 以将其全部包装起来，这似乎“有效” 您可以尝试其中一种或某些元素的组合，然后看看效果如何。

UIView *horizontalLine = [[UIView alloc] initWithFrame:CGRectZero];

[self.view addSubview:horizontalLine];

[horizontalLine setTranslatesAutoresizingMaskIntoConstraints: NO];

horizontalLine.backgroundColor = [UIColor blackColor];

id topGuide = self.topLayoutGuide;
id bottomGuide = self.bottomLayoutGuide;

NSDictionary * viewsDictionary = NSDictionaryOfVariableBindings(horizontalLine, topGuide, bottomGuide);

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[horizontalLine]|" options:0 metrics: 0 views:viewsDictionary]];

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[topGuide][horizontalLine(==3)][bottomGuide]|" options:0 metrics: 0 views:viewsDictionary]];


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

“包裹”方式。它有点乱，但它可能会给你一些尝试的想法

UIView * wrapper = [[UIView alloc] initWithFrame:CGRectZero];

UIView *horizontalLine = [[UIView alloc] initWithFrame:CGRectZero];

[wrapper setTranslatesAutoresizingMaskIntoConstraints: NO];
[horizontalLine setTranslatesAutoresizingMaskIntoConstraints: NO];

[self.view addSubview:wrapper];
[wrapper addSubview:horizontalLine];

horizontalLine.backgroundColor = [UIColor blackColor];

id topGuide = self.topLayoutGuide;
id bottomGuide = self.bottomLayoutGuide;

NSDictionary * viewsDictionary = NSDictionaryOfVariableBindings(horizontalLine, topGuide, bottomGuide, wrapper);

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[wrapper]|" options:0 metrics: 0 views:viewsDictionary]];

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[topGuide][wrapper][bottomGuide]|" options:0 metrics: 0 views:viewsDictionary]];

[wrapper addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[horizontalLine]|" options:0 metrics: 0 views:viewsDictionary]];

[wrapper addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-(>=1)-[horizontalLine(==3)]-(>=1)-|" options:0 metrics: 0 views:viewsDictionary]];

[wrapper addConstraint:
 [NSLayoutConstraint constraintWithItem:horizontalLine
                              attribute:NSLayoutAttributeCenterY
                              relatedBy:NSLayoutRelationEqual
                                 toItem:wrapper
                              attribute:NSLayoutAttributeCenterY
                             multiplier:1
                               constant:0]];