////  AppDelegate.m//  09-控制器View懒加载#import "AppDelegate.h"#import "ViewController.h"@interface AppDelegate ()@end@implementation AppDelegate- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {        // 创建窗口    self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];        // 创建UIViewController控制器，控制器的view并没有创建    // 控制器的view懒加载：第一次使用的时候才会去加载，并不是创建UIViewController控制器的时候去加载    UIViewController *vc = [[ViewController alloc] init];    vc.view.backgroundColor = [UIColor redColor];        self.window.rootViewController = vc;        // 显示窗口    [self.window makeKeyAndVisible];            return YES;}#pragma mark - 控制器view的默认颜色- (void)vcViewBackground{    // Override point for customization after application launch.    self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];        self.window.backgroundColor = [UIColor redColor];        UIButton *btn = [UIButton buttonWithType:UIButtonTypeContactAdd];    btn.center = CGPointMake(20, 100);    [self.window addSubview:btn];        // 默认控制器的view：几乎透明    UIViewController *vc = [[UIViewController alloc] init];    vc.view.backgroundColor = [UIColor clearColor];        //    vc.view.alpha = 0;    //    vc.view.backgroundColor = [UIColor yellowColor];    self.window.rootViewController = vc;            [self.window makeKeyAndVisible];}@end

////  ViewController.m//  09-控制器View懒加载#import "ViewController.h"@interface ViewController ()@end@implementation ViewController- (void)loadView{    // 如果控制器是窗口的根控制器就可以不用设置尺寸    self.view = [[UIView alloc] initWithFrame:CGRectZero];        self.view.backgroundColor = [UIColor yellowColor];    }//- (UIView *)view//{//    if (_view == nil) {//        [self loadView];//        [self viewDidLoad];//    }//    return _view;//}// 在viewDidLoad中打印控制器的尺寸不准确，通常在viewDidAppear// 控制器的view加载完成的时候调用- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view, typically from a nib.        self.view.backgroundColor = [UIColor blueColor];            NSLog(@"%s",__func__);}#pragma mark - view完全显示的时候调用- (void)viewDidAppear:(BOOL)animated{    [super viewDidAppear:animated];    NSLog(@"%@",NSStringFromCGRect(self.view.bounds));    }- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}@end