UIImage *origImage = [UIImage imageNamed:@"fanhui_black"];
//系统返回按钮处的title偏移到可视范围之外
//iOS11 和 iOS11以下分别处理
UIOffset offset = currentSystemVersion.floatValue >= 11.0 ? UIOffsetMake(-200, 0) : UIOffsetMake(0, -80);
[[UIBarButtonItem appearance] setBackButtonTitlePositionAdjustment:offset forBarMetrics:UIBarMetricsDefault];
[[UIBarButtonItem appearance] setBackButtonTitlePositionAdjustment:offset forBarMetrics:UIBarMetricsCompact];
[[UINavigationBar appearance] setBackIndicatorImage:origImage];
[[UINavigationBar appearance] setBackIndicatorTransitionMaskImage:origImage];