iOS设置自定义BackBarButtonItem

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];
}