iOS11之前
[[UIBarButtonItem appearance] setBackButtonTitlePositionAdjustment:UIOffsetMake(0, -60)
forBarMetrics:UIBarMetricsDefault];
iOS 11
[[UIBarButtonItem appearance] setTitleTextAttributes:@{NSFontAttributeName:[UIFont systemFontOfSize:0.1], NSForegroundColorAttributeName: [UIColor clearColor]} forState:UIControlStateNormal];
只需要把文字大小設(shè)置成看不到就可以了