//以下四个条件缺一不可

/.必须是半透明状态

self.navigationBar.translucent = YES;

//2.导航栏背景图片为空图片 (不可以设置backgroundColor或者barTintColor, 没有效果的)

[self.navigationBar setBackgroundImage:[[UIImage alloc]init] forBarMetrics: UIBarMetricsDefault];

//3.阴影图片为空图片 (不可以设置为nil,没用的)

[self.navigationBar setShadowImage:[[UIImage alloc] init]];

//其实到导航栏才44px, 但是backgroundView有64px

self.navigationBar.layer.masksToBounds = YES;

self.navigationController.navigationBar.translucent = NO;

    self.navigationController.navigationBar.shadowImage = [UIImage new];

    UIImage *img = [UIImage imageWithColor:[UIColor greenColor] size:CGSizeMake(, )];

//必须设置一张图片而不是设置背景颜色

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

UITextField *tf = [[UITextField alloc] initWithFrame:CGRectMake(, , , )];

    UIBarButtonItem *item = [[UIBarButtonItem alloc] initWithCustomView:tf];

    self.navigationItem.leftBarButtonItem = item;