解决iOS自定义导航栏左边按钮不能靠左的问题
UIBarButtonItem*item = [[UIBarButtonItemalloc]initWithCustomView:btn];//定义左边按钮
UIBarButtonItem*nagetiveSpacer = [[UIBarButtonItemalloc]initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpacetarget:nilaction:nil];
nagetiveSpacer.width= -12;//这个值可以根据自己需要自己调整
self.navigationItem.leftBarButtonItems=@[nagetiveSpacer,item];
