在扩展类里面:

@implementation UIViewController (BackNavigationBar)

-(void)awakeFromNib{
    [super awakeFromNib];
    self.navigationItem.leftBarButtonItem = [self backButton];
    NSLog(@"test test:%f",self.navigationItem.leftBarButtonItem.customView.frame.origin.x);

}

- (UIBarButtonItem *)backButton
{
    
    UIBarButtonItem * item = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"ic_back" ] style:UIBarButtonItemStylePlain target:self action:@selector(backButtonPressed)];
    
    return item;
}

-(void)backButtonPressed{
    
    [self.navigationController popViewControllerAnimated:YES];
    
}


@end

 注意,如果自定义按钮的图片变形,可能是使用的图片尺寸问题