View的懒加载

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

转载于:https://www.cnblogs.com/Lu2015-10-03/p/5147832.html