在设置navigationItem的leftBarButtonItem或rightBarButtonItem时，

用CustomView初始化UIBarButtonItem，不论怎么设置CustomView的frame，

添加到导航条上之后总是和屏幕边界有一定的间距（5pix），

如何*调整这个间距呢？

下面介绍两种方法：

1、不用直接设置rightBartButtonItem而是设置rightBartButtonItems，并且第一个item设置为一个占位。

- (UIButton *)addRightItemWithTitle:(NSString *)title action:(SEL)action {
  UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
  CGSize size = [title sizeWithFont:[UIFont systemFontOfSize:16]];
  
  //! 这里需要根据内容大小来调整宽度
  button.frame = CGRectMake(0, 0, size.width <= 10 ? 70 : size.width + 10, 44);
  button.titleLabel.textColor = [UIColor whiteColor];
  button.titleLabel.font = [UIFont systemFontOfSize:16];
  button.titleLabel.textAlignment = NSTextAlignmentRight;
  [button setTitle:title forState:UIControlStateNormal];
  /**
   *  width为负数时，相当于btn向右移动width数值个像素，由于按钮本身和边界间距为5pix，所以width设为-15时，间距正好调整
   *  为10；width为正数时，正好相反，相当于往左移动width数值个像素
   */
  UIBarButtonItem *negativeSpacer = [[UIBarButtonItem alloc]
                                     initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace
                                     target:nil action:nil];
  negativeSpacer.width = -15;
  
  [button addTarget:self action:action forControlEvents:UIControlEventTouchUpInside];
  UIBarButtonItem *backItem = [[UIBarButtonItem alloc] initWithCustomView:button];
  self.navigationItem.rightBarButtonItems = @[negativeSpacer, backItem];
  return button;
}

2、如果是只有图片，那么通过设置

[button setImageEdgeInsets:UIEdgeInsetsMake(0, -15, 0, -15)];这样也可以调整

- (UIButton *)addRightItemWithImage:(NSString *)imageName action:(SEL)action {
  UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
  UIImage *image = [UIImage imageNamed:imageName];
  button.frame = CGRectMake(0, 0, image.size.width, image.size.height);
  
  // 这里需要注意：由于是想让图片右移，所以left需要设置为正，right需要设置为负。正在是相反的。
  // 让按钮图片右移15
  [button setImageEdgeInsets:UIEdgeInsetsMake(0, 15, 0, -15)];
  
  [button setImage:image forState:UIControlStateNormal];
  [button addTarget:self action:action forControlEvents:UIControlEventTouchUpInside];
  button.titleLabel.font = [UIFont systemFontOfSize:16];
  UIBarButtonItem *rightItem = [[UIBarButtonItem alloc] initWithCustomView:button];
  self.navigationItem.rightBarButtonItem = rightItem;
  return button;
}