212，三种加载view的方法

• 可以用isViewLoaded方法判断一个UIViewController的view是否已经被加载

AppDelegate.h:

#import <UIKit/UIKit.h>

@class OneViewController;

@class TwoViewController;

@class ThreeViewController;

@interface AppDelegate :UIResponder <UIApplicationDelegate>

@property (strong,nonatomic) UIWindow *window;

@property (nonatomic,strong)OneViewController *kOmeView;

@property (nonatomic,strong)TwoViewController *kTwoView;

@property (nonatomic,strong)ThreeViewController *kThreeView;

@end

AppDelegate.h:

    self.window =[[UIWindowalloc] initWithFrame:[UIScreenmainScreen].bounds];

    //1，使用纯代码创建view

    self.kOmeView = [[OneViewControlleralloc] init];

    self.window.rootViewController =self.kOmeView;

    

    //2，使用xib加载

    self.kTwoView = [[TwoViewControlleralloc] initWithNibName:@"TwoViewController"bundle:nil];

    self.window.rootViewController =self.kTwoView;

    

    //3，使用storyboard加载

    UIStoryboard *storyboard  = [UIStoryboardstoryboardWithName:@"ThreeViewController"bundle:nil];

    self.kThreeView = [storyboardinstantiateInitialViewController];

    self.window.rootViewController =self.kThreeView;

    [self.windowmakeKeyAndVisible];