//设置全局返回按钮

UIImage *backButtonImage = [[UIImage imageNamed:@"arrow-right"] resizableImageWithCapInsets:UIEdgeInsetsMake(0, 0, 0, 0)];

[[UIBarButtonItem appearance] setBackButtonBackgroundImage:backButtonImage forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];

//适配ios11    返回按钮和导航栏在一条直线上

if(@available(iOS11.0,*)) {

        [[UIBarButtonItem appearance] setBackButtonTitlePositionAdjustment:UIOffsetMake(-200,0) forBarMetrics:UIBarMetricsDefault];

    }else{

       [[UIBarButtonItem appearance] setBackButtonTitlePositionAdjustment:UIOffsetMake(0, -60)forBarMetrics:UIBarMetricsDefault];

    }