控制器的创建

• 通过storyboard

// 加载storyboard
// storyboard文件名，不需要带后缀
// nil:  [NSBundle mainBundle]
UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
// 通过storyboard创建控制器
// instantiateInitialViewController：加载箭头指向的控制器
UIViewController *vc = [storyboard instantiateInitialViewController];
//加载指定标识的控制器
UIViewController *vc = [storyboard instantiateViewControllerWithIdentifier:@"green"];

• 通过xib

// 通过xib创建控制器
YWViewController *vc = [[YWViewController alloc] initWithNibName:@"YWViewController" bundle:nil];

- 注意点
1、需要设置xib的`File's Owner`的Custom Class
2、需要给`File's Owner`的Outlets中的view连线

If the view controller class name ends with the word ‘Controller’, as in MyViewController, it looks for a nib file whose name matches the class name without the word ‘��Controller’, as in MyView.nib. It looks for a nib file whose name matches the name of the view controller class. For example, if the class name is MyViewController, it looks for a MyViewController.nib file.

4、如果第二点没有连线，报错信息：
reason: '-[UIViewController _loadViewFromNibNamed:bundle:] loaded the "YWViewController" nib but the view outlet was not set.'

• 手动创建

YWViewController *vc = [[YWViewController alloc] init];

- 手动创建的麻烦的地方就是所有东西都需要自己去写代码创建

5、使用storyboard创建控制器的时候，通常需要从一个控制器跳转到另一个控制器，这个时候就需要执行一些特殊的方法

//执行跳转
[self performSegueWithIdentifier:@"目标控制器的ID" sender:nil];

// 在执行跳转之前的时候调用
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    // 源控制器
    segue.sourceViewController
    //目标控制器
    segue.destinationViewController
}