UIBarButtonItem *backBtnItem = [[UIBarButtonItem alloc] init];
UIImage* backButtonBackgroundImage = [UIImage imageNamed:@"navigation_backBtn"];
//设置图片不拉伸
[backBtnItem setBackButtonBackgroundImage:[backButtonBackgroundImage resizableImageWithCapInsets:UIEdgeInsetsMake(0, backButtonBackgroundImage.size.width, 0, 0)] forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];
//title设置为空，或者将title移动到看不到的地方（我这里替换为空）
backBtnItem.title = @"";
// [backBtnItem setBackButtonTitlePositionAdjustment:UIOffsetMake(-400.f, 0) forBarMetrics:UIBarMetricsDefault];
self.navigationItem.backBarButtonItem = backBtnItem;
如果要全局设置，要么是自己写一个继承类
或者在app的didFinishLaunching里的[UIBarButtonItem appearance]替换
