iOS11下，leftBarButtonItem异常情况
一般leftBarButtonItem加载网络图片或因为其他问题，必须要在leftBarButtonItem使用自定义的UIButton时，就会因为图片太大，导致设置为UIButton的背景图片时，因为图片太大，拉宽leftBarButtonItem。如下图：
被拉宽的leftBarButtonItem
原始的方法为xib文件或者是自定义的：
UIButton *leftCustomButton = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 35, 35)];
[leftCustomButton setBackgroundImage:[UIImage imageNamed:@"defaultImage"] forState:UIControlStateNormal];
UIBarButtonItem * leftButtonItem =[[UIBarButtonItem alloc] initWithCustomView:leftCustomButton];
self.navigationItem.leftBarButtonItems = @[self.headerIconItem];
但是直接设置UIButton的frame在iOS 11下是没有作用的，解决方法如下：
UIButton *leftCustomButton = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 35, 35)];
[leftCustomButton setBackgroundImage:[UIImage imageNamed:@"defaultImage"] forState:UIControlStateNormal];
UIView *leftCustomView = [[UIView alloc] initWithFrame: leftCustomButton.frame];
[leftCustomView addSubview: leftCustomButton];
UIBarButtonItem * leftButtonItem =[[UIBarButtonItem alloc] initWithCustomView: leftCustomView];
self.navigationItem.leftBarButtonItems = @[self.headerIconItem];
即在UIButton上在包装一层UIView，即可实现修改leftBarButtonItem的大小。
修改之后如下图：
正常大小的leftBarButtonItem
