ios导航栏图片自适应, 根据图片大小适配

 UIImage *backGroundImage = [UIImage imageNamed:@"home_detail_head.png"];

    backGroundImage = [backGroundImage resizableImageWithCapInsets:UIEdgeInsetsZero resizingMode:UIImageResizingModeStretch];

    [self.navigationController.navigationBar setBackgroundImage:backGroundImage forBarMetrics:UIBarMetricsDefault];