自定义backBarButtonItem ，保留动画

UIImage *backButtonImage = [[UIImage imageNamed:@"backbar_icon.png"] resizableImageWithCapInsets:UIEdgeInsetsMake(0, 10, 0, 0)];[[UIBarButtonItem appearance] setBackButtonBackgroundImage:backButtonImage  forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];[[UIBarButtonItem appearance] setBackButtonTitlePositionAdjustment:UIOffsetMake(2, 0) forBarMetrics:UIBarMetricsDefault];[[UIBarButtonItem appearance] setTitleTextAttributes: @{NSForegroundColorAttributeName:[UIColor grayColor]} forState:UIControlStateNormal];[[UIBarButtonItem appearance] setTitleTextAttributes: @{NSForegroundColorAttributeName:[<pre name="code" class="objc">UIColor grayColor

]} forState:UIControlStateHighlighted];

背景图片的尺寸，和UIEdgeInsetsMask有技巧，需要设置Higlighted颜色