ios - 无法缩小 UIWebView 和 UINavigationBar 之间的差距

Question

在我的项目中，我在 UINavigationBar 下放置了一个 UIWebView 并设置 UIWebView 以占据除 以外的屏幕其余部分UINavigationBar.但是我发现两个控件之间存在一些差距。左边缘和 UIWebView 左侧之间也有间隙。知道我错过了什么吗？

这是我更新后的代码:在 UIView+AutoLayout 中:(此类别会将所有 View 的 translatesAutoresizingMaskIntoConstraints 属性设置为 NO)

#import "UIView+AutoLayout.h"

@implementation UIView (AutoLayout)
+ (id)autolayoutView
{
    UIView *view = [self new];
    view.translatesAutoresizingMaskIntoConstraints = NO;
    return view;
}
@end

在 View Controller 中:

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.navigationBar = [UINavigationBar autolayoutView];
    UINavigationItem *backToListItem = [[UINavigationItem alloc] init];
    UIBarButtonItem *listItem = [[UIBarButtonItem alloc] initWithTitle:@"List"   style:UIBarButtonItemStylePlain target:self action:@selector(listButtonPressed:)];
    backToListItem.leftBarButtonItem = listItem;

    self.navigationBar.items = [NSArray arrayWithObject:backToListItem];

    [self.view addSubview:self.navigationBar];

    self.webView = [TNSWebView autolayoutView];

    [self.view addSubview:self.webView];

    NSDictionary *views = NSDictionaryOfVariableBindings(_navigationBar, _webView);
    [self.view addConstraints:[NSLayoutConstraint
                           constraintsWithVisualFormat:@"|[_navigationBar]|"
                           options:0 metrics:nil
                           views:views]];
    [self.view addConstraints:[NSLayoutConstraint
                                 constraintsWithVisualFormat:@"V:|[_navigationBar]->=0-[_webView]|"
                                 options:0 metrics:nil
                                 views:views]];
    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[_webView]|" options:0 metrics:nil views:views]];
    [self.webView setupVideoPlayer:self.videoId];
}

在 lldb 中使用 po [[UIWindow keyWindow] recursiveDescription] 命令我得到了这个结果

    | <UIView: 0x1d23f880; frame = (0 20; 768 1004); autoresize = RM+BM; layer = <CALayer: 0x1d23cba0>>
   |    | <UINavigationBar: 0x1d00a4b0; frame = (0 0; 768 44); gestureRecognizers = <NSArray: 0x1d015ff0>; layer = <CALayer: 0x1d0c8f60>>
   |    |    | <_UINavigationBarBackground: 0x1d010250; frame = (0 0; 768 44); opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1d011140>>
   |    |    |    | <UIImageView: 0x1d0d26b0; frame = (0 44; 768 3); opaque = NO; autoresize = W+TM; userInteractionEnabled = NO; layer = <CALayer: 0x1d23fbd0>>
   |    |    | <UINavigationItemView: 0x1d016740; frame = (384 22; 0 0); opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1d016840>>
   |    |    | <UINavigationButton: 0x1d013ff0; frame = (7 7; 48 30); opaque = NO; layer = <CALayer: 0x1d014170>>
   |    |    |    | <UIImageView: 0x1c5d9ca0; frame = (0 0; 48 30); clipsToBounds = YES; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1c58b330>>
   |    |    |    | <UIButtonLabel: 0x1d0144c0; frame = (13 7; 22 15); text = 'List'; clipsToBounds = YES; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1d014560>>
   |    | <TNSWebView: 0x1d016bc0; baseClass = UIWebView; frame = (0 44; 768 960); layer = <CALayer: 0x1d016ca0>>
   |    |    | <_UIWebViewScrollView: 0x1d012390; frame = (0 0; 768 960); clipsToBounds = YES; autoresize = H; gestureRecognizers = <NSArray: 0x1d011380>; layer = <CALayer: 0x1d0125e0>; contentOffset: {0, 0}>
   |    |    |    | <UIImageView: 0x1d00f2a0; frame = (0 0; 10 10); transform = [-1, 0, -0, -1, 0, 0]; alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1d00f300>>
   |    |    |    | <UIImageView: 0x1d00f210; frame = (0 0; 10 10); transform = [0, 1, -1, 0, 0, 0]; alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1d00f270>>
   |    |    |    | <UIImageView: 0x1d00f180; frame = (0 0; 10 10); transform = [0, -1, 1, 0, 0, 0]; alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1d00f1e0>>
   |    |    |    | <UIImageView: 0x1d00efb0; frame = (0 0; 10 10); alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1d00f150>>
   |    |    |    | <UIImageView: 0x1d00ef20; frame = (-4.5 4.5; 10 1); transform = [0, 1, -1, 0, 0, 0]; alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1d00ef80>>
   |    |    |    | <UIImageView: 0x1d00ee90; frame = (-4.5 4.5; 10 1); transform = [0, -1, 1, 0, 0, 0]; alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1d00eef0>>
   |    |    |    | <UIImageView: 0x1d00ee00; frame = (0 0; 1 10); transform = [-1, 0, -0, -1, 0, 0]; alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1d00ee60>>
   |    |    |    | <UIImageView: 0x1d00ec30; frame = (0 0; 1 10); alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1d00edd0>>
   |    |    |    | <UIImageView: 0x1d00eba0; frame = (0 954; 768 6); alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1d00ec00>>
   |    |    |    | <UIImageView: 0x1d00fcd0; frame = (0 0; 768 6); transform = [-1, 0, -0, -1, 0, 0]; alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1d00fe70>>
   |    |    |    | <UIWebBrowserView: 0x1dbf2400; frame = (0 0; 768 960); gestureRecognizers = <NSArray: 0x1d014c40>; layer = <UIWebLayer: 0x1d017d00>>
   |    |    |    |    | <TileHostLayer: 0x1d017e70> (layer)
   |    |    |    |    |    | <TileLayer: 0x1c5511a0> (layer)
   |    |    |    |    |    | <TileLayer: 0x1c551210> (layer)
   |    |    |    |    |    | <TileLayer: 0x1c551250> (layer)
   |    |    |    |    |    | <TileLayer: 0x1c551290> (layer)

更新后的截图:

只需将导航栏的高度更改为 44 并使用 recursiveDescription 命令，我得到:

$0 = 0x2008f680 <UIWindow: 0x1ed814f0; frame = (0 0; 768 1024); autoresize = W+H; layer = <UIWindowLayer: 0x1ed815f0>>
   | <UIView: 0x20167680; frame = (0 20; 768 1004); autoresize = RM+BM; layer = <CALayer: 0x1ed0ea50>>
   |    | <UINavigationBar: 0x1ed14b70; frame = (0 0; 768 44); gestureRecognizers = <NSArray: 0x20081bd0>; layer = <CALayer: 0x1ed09ff0>>
   |    |    | <_UINavigationBarBackground: 0x1ed8b9b0; frame = (0 0; 768 44); opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1ed08570>>
   |    |    |    | <UIImageView: 0x2007aa90; frame = (0 44; 768 3); opaque = NO; autoresize = W+TM; userInteractionEnabled = NO; layer = <CALayer: 0x200f9640>>
   |    |    | <UINavigationItemView: 0x20053320; frame = (384 22; 0 0); opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x200f9c30>>
   |    |    | <UINavigationButton: 0x200fa980; frame = (7 7; 48 30); opaque = NO; layer = <CALayer: 0x200f50c0>>
   |    |    |    | <UIImageView: 0x2016af20; frame = (0 0; 48 30); clipsToBounds = YES; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x2016af80>>
   |    |    |    | <UIButtonLabel: 0x2004e420; frame = (13 7; 22 15); text = 'List'; clipsToBounds = YES; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x200f8040>>
   |    | <TNSWebView: 0x2004d660; baseClass = UIWebView; frame = (0 44; 768 960); layer = <CALayer: 0x20053f20>>
   |    |    | <_UIWebViewScrollView: 0x2004a230; frame = (0 0; 768 960); clipsToBounds = YES; autoresize = H; gestureRecognizers = <NSArray: 0x20049700>; layer = <CALayer: 0x2004a6c0>; contentOffset: {0, 0}>
   |    |    |    | <UIImageView: 0x20048d50; frame = (0 0; 10 10); transform = [-1, 0, -0, -1, 0, 0]; alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x20048db0>>
   |    |    |    | <UIImageView: 0x20048cc0; frame = (0 0; 10 10); transform = [0, 1, -1, 0, 0, 0]; alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x20048d20>>
   |    |    |    | <UIImageView: 0x20048c30; frame = (0 0; 10 10); transform = [0, -1, 1, 0, 0, 0]; alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x20048c90>>
   |    |    |    | <UIImageView: 0x200f7c50; frame = (0 0; 10 10); alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x20048c00>>
   |    |    |    | <UIImageView: 0x200f7bc0; frame = (-4.5 4.5; 10 1); transform = [0, 1, -1, 0, 0, 0]; alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x200f7c20>>
   |    |    |    | <UIImageView: 0x200f7b30; frame = (-4.5 4.5; 10 1); transform = [0, -1, 1, 0, 0, 0]; alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x200f7b90>>
   |    |    |    | <UIImageView: 0x200f7a30; frame = (0 0; 1 10); transform = [-1, 0, -0, -1, 0, 0]; alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x200f7b00>>
   |    |    |    | <UIImageView: 0x200f7890; frame = (0 0; 1 10); alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x200f7a00>>
   |    |    |    | <UIImageView: 0x200fad20; frame = (0 954; 768 6); alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x200fad80>>
   |    |    |    | <UIImageView: 0x200fab80; frame = (0 0; 768 6); transform = [-1, 0, -0, -1, 0, 0]; alpha = 0; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x200facf0>>
   |    |    |    | <UIWebBrowserView: 0x1fb37600; frame = (0 0; 768 960); gestureRecognizers = <NSArray: 0x20049910>; layer = <UIWebLayer: 0x200f81c0>>
   |    |    |    |    | <TileHostLayer: 0x2004ed10> (layer)
   |    |    |    |    |    | <TileLayer: 0x20168820> (layer)
   |    |    |    |    |    | <TileLayer: 0x20168890> (layer)
   |    |    |    |    |    | <TileLayer: 0x201688d0> (layer)
   |    |    |    |    |    | <TileLayer: 0x20168910> (layer)

Answer 1

更新

我收回这一切。您的问题不在于 View 布局。我相信您的问题是您加载到 WebView 中的网络内容周围有边框(或填充或边距)。你可能会发现 “Debugging Web Content on iOS”有用。它解释了如何使用 Safari(在您的 Mac 上)中的 Web Inspector 来调试在模拟器或设备上运行的 UIWebView 中的内容。我认为如果您检查 Web 内容中的视频元素，您会发现它没有与视口(viewport)的顶部和左侧边距齐平。

原创

我猜想当您在 viewDidLoad 中查看时，导航栏的高度设置不正确。现在检查您刚刚创建的 View 框架还为时过早。

一个 iOS 应用程序在一个“运行循环”中度过它的时间，看起来像这样:

while (1) {
    Event phase: process one event (e.g. touch event, timer firing, local or push notification, etc.)
    Layout phase: update the frames of new views and views with added or removed subviews
    Draw phase: draw the contents of views that need to be drawn
    Wait for the next event to arrive
}

当您将 View 添加到 View 层次结构时，它们会在布局阶段安排好布局。直到布局阶段完成后，您才能依靠新 View 来获得适当的框架。

您可以通过编写 UIView 的子类(或必要时任何其他 View 类的子类)并覆盖其 layoutSubviews 方法来进入布局阶段。或者您可以在 View Controller 中实现 viewDidLayoutSubviews 方法。我建议使用 UIView 子类并覆盖 layoutSubviews，但您可能会发现仅实现 viewDidLayoutSubviews 更方便:

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];
    [self layoutWebView];
}

- (void)layoutWebView {
    CGRect frame = self.view.bounds;
    CGFloat navBarHeight = self.navigationBar.frame.size.height;
    frame.origin.y = navBarHeight;
    frame.size.height -= navBarHeight;
    self.webView.frame = frame;
}

或者，如果您的部署目标是 iOS 6 或更高版本，您可以使用自动布局将导航栏的底部边缘固定到 WebView 的顶部边缘。把它放在 viewDidLoad 中:

[self.view addLayoutConstraints:[NSLayoutConstraint
    constraintsWithVisualFormat:@"|V:[_navigationBar][_webView]|"
    options:0 metrics:nil
    views:NSDictionaryOfVariableBindings(_navigationBar, _webView)]];

现在，我认为您的应用中具体发生的事情是您在创建 UINavigationBar 时将高度指定为 50，但是 UINavigationBar 需要高度44. 因此在布局阶段，导航栏将自身调整为 44 点高。由于您在布局期间没有做任何事情来修复 Web View 的框架，因此 Web View 仍然比顶级 View 的顶部边缘低 50 点，留下 6 点的差距。因此，您可以在创建导航栏时将导航栏的高度更改为 44。 ;^)