BackBarButtonItem 层级结构
首先我们看一下返回按钮的导航栏视图的结构层次，因为导航栏的视图加载以及初始化跟viewController的view不一样，不能再veiwDidLoad中去观察（viewWillAppear中也不行）要在viewDidLoad中才可以看到完整的导航栏视图结构层次。我们可以在一个有去掉文字的返回按钮控制器的viewDidApper中打上断点然后在控制台执行：
po [[UIWindow keyWindow] recursiveDescription]
打印结果：
<UIWindow: 0x7fc56e7051c0; frame = (0 0; 414 896); gestureRecognizers = <NSArray: 0x6000026ee580>; layer = <UIWindowLayer: 0x6000028ee320>>
| <UILayoutContainerView: 0x7fc56e705d80; frame = (0 0; 414 896); autoresize = W+H; gestureRecognizers = <NSArray: 0x6000026ef4e0>; layer = <CALayer: 0x6000028ee060>>
| | <UINavigationTransitionView: 0x7fc56e708270; frame = (0 0; 414 896); clipsToBounds = YES; autoresize = W+H; layer = <CALayer: 0x6000028eec60>>
| | | <UIViewControllerWrapperView: 0x7fc56e605850; frame = (0 0; 414 896); autoresize = W+H; layer = <CALayer: 0x6000028a5880>>
| | | | <UIView: 0x7fc56e50fa40; frame = (0 0; 414 896); autoresize = W+H; layer = <CALayer: 0x6000028abde0>>
| | | | | <UIButton: 0x7fc56e5039e0; frame = (172 230; 52 30); opaque = NO; autoresize = RM+BM; layer = <CALayer: 0x6000028abc80>>
| | | | | | <UIButtonLabel: 0x7fc56e603770; frame = (0.5 6; 51.5 18); text = 'GoNext'; alpha = 0.2; opaque = NO; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x600000bd0690>>
| | <UINavigationBar: 0x7fc56e4107d0; frame = (0 44; 414 44); opaque = NO; autoresize = W; layer = <CALayer: 0x6000028c2ec0>>
| | | <_UIBarBackground: 0x7fc56e410a90; frame = (0 -44; 414 88); userInteractionEnabled = NO; layer = <CALayer: 0x6000028c2f20>>
| | | | <UIImageView: 0x7fc56e411620; frame = (0 88; 414 0.5); userInteractionEnabled = NO; layer = <CALayer: 0x6000028c2f60>>
| | | | <UIVisualEffectView: 0x7fc56e411850; frame = (0 0; 414 88); layer = <CALayer: 0x6000028c2f80>>
| | | | | <_UIVisualEffectBackdropView: 0x7fc56e706750; frame = (0 0; 414 88); autoresize = W+H; userInteractionEnabled = NO; layer = <UICABackdropLayer: 0x6000028ee9e0>>
| | | | | <_UIVisualEffectSubview: 0x7fc56e707810; frame = (0 0; 414 88); autoresize = W+H; userInteractionEnabled = NO; layer = <CALayer: 0x6000028eec80>>
| | | <_UINavigationBarLargeTitleView: 0x7fc56e4125f0; frame = (0 0; 0 50); clipsToBounds = YES; hidden = YES; layer = <CALayer: 0x6000028c3140>>
| | | | <UILabel: 0x7fc56e4137b0; frame = (0 0; 0 0); userInteractionEnabled = NO; layer = <_UILabelLayer: 0x600000bcc9b0>>
| | | <_UINavigationBarContentView: 0x7fc56e411c80; frame = (0 0; 414 44); layer = <CALayer: 0x6000028c2fc0>>
| | | | <UILabel: 0x7fc56e503580; frame = (147.5 12; 119 20.5); text = 'ViewController'; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x600000bc8c80>>
| | | <_UINavigationBarModernPromptView: 0x7fc56e608a20; frame = (0 0; 0 50); alpha = 0; hidden = YES; layer = <CALayer: 0x6000028a4840>>
设置BackBarButtonItem
1.文字偏移法
#pragma mark - 自定义系统自带的backBarButtomItem
// 去掉系统默认自带的文字（上一个控制器的title），修改系统默认的样式（一个蓝色的左箭头）为自己的图片
-(void)customBackBarButtonItem {
// 去掉文字
// 自定义全局的barButtonItem外观
UIBarButtonItem *barButtonItemAppearance = [UIBarButtonItem appearance];
// 将文字减小并设其颜色为透明以隐藏
[barButtonItemAppearance setTitleTextAttributes:@{NSFontAttributeName: [UIFont systemFontOfSize:0.1], NSForegroundColorAttributeName: [UIColor clearColor]} forState:UIControlStateNormal];
// 设置图片
// 获取全局的navigationBar外观
UINavigationBar *navigationBarAppearance = [UINavigationBar appearance];
// 获取原图
UIImage *image = [[UIImage imageNamed:@"navigationbar_back"] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
// 修改navigationBar上的返回按钮的图片，注意：这两个属性要同时设置
navigationBarAppearance.backIndicatorImage = image;
navigationBarAppearance.backIndicatorTransitionMaskImage = image;
}
缺点：打开相册等，系统自带的导航条右侧的取消按钮也是透明的，看不见了
2.文字透明法
- (void)setNaviBack{
UINavigationBar * navigationBar = [UINavigationBar appearance];
//返回按钮的箭头颜色
[navigationBar setTintColor:[UIColor colorWithRed:0.984 green:0.000 blue:0.235 alpha:1.000]];
//设置返回样式图片
UIImage *image = [UIImage imageNamed:@"navi_back"];
image = [image imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
navigationBar.backIndicatorImage = image;
navigationBar.backIndicatorTransitionMaskImage = image;
UIBarButtonItem *buttonItem = [UIBarButtonItem appearanceWhenContainedIn:[UINavigationBar class], nil];
UIOffset offset;
offset.horizontal = - 500;
offset.vertical = - 500;
[buttonItem setBackButtonTitlePositionAdjustment:offset forBarMetrics:UIBarMetricsDefault];
}
缺点：
1.导航条上的返回按钮 的 相应区域 还是原来那么大 没有变为图片的大小
2.第一个界面的 title 过长 会影响 跳转到的第二界面 的 title
因为没有去改变系统的backBarButtonItem，所以位置是没有变的。
3.设置 setBackButtonTitlePositionAdjustment还会导致一个问题,就是在做分享或者是支付,跳转其他APP(eg:支付宝,微信)之后,返回自己的APP的时候,会出现屏幕闪动的BUG,建议不要使用这个方法来做.
3.综合方案
以下代码写在自定义的导航控制器中
1.替换系统默认返回图片
- (void)viewDidLoad {
[super viewDidLoad];
self.delegate = self;
// 自定义返回图片(在返回按钮旁边) 这个效果由navigationBar控制
[self.navigationBar setBackIndicatorImage:[UIImage imageNamed:@"NavBack"]];
[self.navigationBar setBackIndicatorTransitionMaskImage:[UIImage imageNamed:@"NavBack"]];
}
2.去掉文字
- (void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated
{
if (self.viewControllers.count > 0) {
viewController.hidesBottomBarWhenPushed = YES;
}
// 去掉系统backBarButtonItem的默认显示效果
// 这个效果由控制器控制(A push B 则在A中设置)
/***
1、如果B视图有一个自定义的左侧按钮（leftBarButtonItem），则会显示这个自定义按钮；
2、如果B没有自定义按钮，但是A视图的backBarButtonItem属性有自定义项，则显示这个自定义项；
3、如果前2条都没有，则默认显示一个后退按钮，后退按钮的标题是A视图的标题。
*/
UIBarButtonItem *item = [[UIBarButtonItem alloc] initWithTitle:@"" style:UIBarButtonItemStylePlain target:nil action:NULL];
viewController.navigationItem.backBarButtonItem = item;
[super pushViewController:viewController animated:animated];
}
