问UINavigtion控制器后退按钮显示不正确

EN

    var backImage = UIImage(named: "back_button_image").withRenderingMode(.alwaysOriginal)
    let leftPadding: CGFloat = 10
    let adjustSizeForBetterHorizontalAlignment: CGSize = CGSize(width: backImage.size.width + leftPadding, height: backImage.size.height)
    UIGraphicsBeginImageContextWithOptions(adjustSizeForBetterHorizontalAlignment, false, 0)
    backImage.draw(at: CGPoint(x: leftPadding, y: 0))
    backImage = UIGraphicsGetImageFromCurrentImageContext()!
    UIGraphicsEndImageContext()
    self.navigationController?.navigationBar.backIndicatorImage = backImage
    self.navigationController?.navigationBar.backIndicatorTransitionMaskImage = backImage
    self.navigationItem.backBarButtonItem = UIBarButtonItem(title: " ", style: .plain, target: nil, action: nil)