Question

我试图在具有导航栏的应用程序的屏幕中间画一条水平线。这是我目前的代码：

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 - 这很好用。但问题是，无论设备如何，这条水平线在屏幕上的亮度都会大约为10像素。我可能会错过一个偏移吗？可能与导航栏有关吗？

Answer 1

好吧，我先这样做了..但它没有居中。但它应该是！ :) 在这个下面我改变了它来添加一个视图来包装所有这些似乎＆＃34;工作＆＃34; 您可以尝试使用或者或者某些元素的组合，看看它是如何发生的。

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]];

＆＃34;包裹＆＃34;做法。它有点乱，但它可能会给你一些想法的想法

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]];

Answer 2

好吧，我喜欢@ myte的解决方案。如果我正在使用相同的功能，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。状态栏通常为20像素高。当你除以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];

PS：你提到问题是＆＃34;无论设备是什么＆＃34;但是，如果你在横向模式的iPhone 4S上试用它，它可能只是居中，因为状态栏被隐藏：P （link）。

Objective-C - 在屏幕中间绘制一条水平线

2 个答案: