UINavigationBar 添加UIImage背景
UIImage *myImage = [UIImage imageNamed:@"logobg.png"];
UIImageView *myImageView = [[UIImageView alloc]initWithImage:myImage];
[[UINavigationBar appearance]addSubview:myImageView];
UIImage *myImage = [UIImage imageNamed:@"logobg.png"];
UIImageView *myImageView = [[UIImageView alloc]initWithImage:myImage];
[[UINavigationBar appearance]addSubview:myImageView];