Objective-C - 在屏幕中间画一条水平线答案

【问题标题】：Objective-C - drawing a horizontal line through the middle of the screenObjective-C - 在屏幕中间画一条水平线
【发布时间】：2015-01-17 19:48:11
【问题描述】：

我正在尝试在具有导航栏的应用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];

我使用了一个非常相似的计算来绘制一条垂直线——效果很好。但是，问题是，无论设备如何，这条水平线在屏幕上的位置都太低了大约 10 个像素。是否有我可能缺少的偏移量？也许与导航栏有关？

【问题讨论】：

你是说状态栏高度？
我的意思是使用导航控制器的导航栏

标签： ios objective-c cgrectmake

【解决方案1】：

好的，我先这样做了..但它没有居中。但它应该是！ :) 在此我更改了它以添加一个视图来包装它，这似乎“工作” 您可以尝试其中一种或几种元素的组合，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]];

“包装”的方法。这有点乱，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]];

【讨论】：

【解决方案2】：

嗯，我确实喜欢@myte 的解决方案。如果我在做同样的功能，我也会使用NSLayoutConstraint。但是，要直接回答您的问题，您缺少的是状态栏。状态栏的高度通常为 20 像素。当你将它除以 2 时，你会得到 10 个像素。

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;

// This is what you are missing
CGFloat statusBarHeight = [[UIApplication sharedApplication] statusBarFrame].size.height;

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

P.S.：您提到问题是“与设备无关”，但是，如果您在 iPhone 4S 上以横向模式尝试它，它可能只是居中，因为状态栏是隐藏的 :P (link) .

【讨论】：