iOS 14中长按返回按钮会显示多级菜单，滑动后可以返回对应的页面。
navigation stack.gif
在App上长按后title为空
空白.png
backButtonDisplayMode
iOS 14新增了一个属性backButtonDisplayMode来定义title的来源
typedef NS_ENUM(NSInteger, UINavigationItemBackButtonDisplayMode) {
/// Default mode, uses an appropriate title, followed by a generic title (typically 'Back'), then no title.
UINavigationItemBackButtonDisplayModeDefault = 0,
/// Generic titles only. Ignores .title and .backButtonTitle (but *not* .backBarButtonItem.title).
UINavigationItemBackButtonDisplayModeGeneric = 1,
/// Don't use a title, just the back button indicator image.
UINavigationItemBackButtonDisplayModeMinimal = 2,
} NS_SWIFT_NAME(UINavigationItem.BackButtonDisplayMode);
title来源的优先级
1.navigationItem.backBarButtonItem
2.navigationItem.backButtonTitle
3.navigationItem.title和viewController的title，同时设置显示为viewController的title
App中使用
UIBarButtonItem *item = [[UIBarButtonItem alloc] initWithTitle:@"" style:UIBarButtonItemStylePlain target:nil action:nil];
self.navigationItem.backBarButtonItem = item;
来隐藏返回按钮的标题，引起了上面的问题。
UINavigationItemBackButtonDisplayModeMinimal
Minimal模式下，返回按钮不显示title，但是 navigation stack可以显示出 title,未设置title的时候显示返回。
适配
if (@available(iOS 14.0, *)) {
self.navigationItem.backButtonDisplayMode = UINavigationItemBackButtonDisplayModeMinimal;
} else {
UIBarButtonItem *item = [[UIBarButtonItem alloc] initWithTitle:@"" style:UIBarButtonItemStylePlain target:nil action:nil];
self.navigationItem.backBarButtonItem = item;
}
适配.png
