AppDelegate.m
#import "AppDelegate.h"
#import "ViewController.h"
@interface AppDelegate ()
@end
@implementation AppDelegate
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
// Override point for customization after application launch.
UIWindow *window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
ViewController *vc = [[ViewController alloc] init];
// vc.view.backgroundColor = [UIColor purpleColor];//view的懒加载 View 的懒加载只有需要的时候才加载
// NSLog(@"aaaaaa");
window.rootViewController = vc;
NSLog(@"aaaaaaa");
//显示控制器view
[window makeKeyAndVisible];
NSLog(@"bbbbbb");
self.window = window;
return YES;
}
ViewController.m
#import "ViewController.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
NSLog(@"%s",__func__);
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
另一种情况
#import "AppDelegate.h"
#import "ViewController.h"
@interface AppDelegate ()
@end
@implementation AppDelegate
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
// Override point for customization after application launch.
UIWindow *window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
ViewController *vc = [[ViewController alloc] init];
vc.view.backgroundColor = [UIColor purpleColor];//view的懒加载 View 的懒加载只有需要的时候才加载
NSLog(@"aaaaaa");
window.rootViewController = vc;
// NSLog(@"aaaaaaa");
//显示控制器view
[window makeKeyAndVisible];
NSLog(@"bbbbbb");
self.window = window;
return YES;
}
1.懒加载基本
懒加载——也称为延迟加载，即在需要的时候才加载（效率低，占用内存小）。所谓懒加载，写的是其get方法.
注意：如果是懒加载的话则一定要注意先判断是否已经有了，如果没有那么再去进行实例化
2.使用懒加载的好处：
（1）不必将创建对象的代码全部写在viewDidLoad方法中，代码的可读性更强
（2）每个控件的getter方法中分别负责各自的实例化处理，代码彼此之间的独立性强，松耦合