self.title = @"下载微课";//在有navigationController的控制器中，作用与self.navigationItem.title = @"下载微课";相同

[self.navigationController.navigationBar setTitleTextAttributes:

  @{NSFontAttributeName:[UIFont systemFontOfSize:18],

    NSForegroundColorAttributeName:[UIColor whiteColor]}];//系统方法

self.navigationItem.title = @"下载微课";

//修改导航栏

UILabel *titleLable = [[UILabel alloc]initWithFrame:CGRectMake(0,0,100,30)];

titleLable.text = @"下载微课";

titleLable.textColor = [UIColor whiteColor];

titleLable.font = [UIFont systemFontOfSize:18];

self.navigationItem.titleView = titleLable;