加载storyboard和xib文件

// 加载storyboard
UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Two" bundle:nil];

// 创建storyboard里面灰色的控制器
　　　//找到shtoryboard里面设置的初始控制器
//    UIViewController *vc = [storyboard instantiateInitialViewController];
　　
　　// 从storyboard里面找出绑定标识的控制器
MJTwoViewController *vc = [storyboard instantiateViewControllerWithIdentifier:@"pink"];
self.window.rootViewController = vc;

//nib文件初始化
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
// Custom initialization
}
return self;
}
//加载所有xib文件

NSArray* objects = [[NSBundle mainBundle] loadNibNamed:nibName owner:self options:nil]

//加载指定xib文件

ContactsTableViewCell  *cell = [[[NSBundle mainBundle]loadNibNamed:@"ContactsTableViewCell" owner:nil options:nil] objectAtIndex:0]

-(instancetype)initWithFrame:(CGRect)frame
{
self=[super initWithFrame:frame];
if (self) {
//NIb加载会把xib文件加载到内存中，读取快，经常使用的xib文件可以使用nib加载，
　　　　//Bundle加载，每次会从磁盘上加载，效率会慢一点
//        self=[[[UINib nibWithNibName:@"MPListView" bundle:nil] instantiateWithOwner:self options:nil] lastObject];
self=[[[NSBundle mainBundle] loadNibNamed:@"MPListView" owner:self options:nil] objectAtIndex:0];
}

return self;
}