OC的懶加載

#import "DemoViewController.h"@interface DemoViewController ()@PRoperty (nonatomic, strong) UILabel *label;@end@implementation DemoViewController- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view.        [self.view addSubview:self.label];        //釋放label    _label = nil;        //會再次調用懶加載    NSLog(@"%@", self.label);}-(UILabel *)label{    if (_label == nil) {        _label = [[UILabel alloc] init];        _label.text = @"my hello";        _label.center = self.view.center;        [_label sizeToFit];    }    return _label;}- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];            //收到內存警告，可以釋放視圖    //On iOS 6.0 it will no longer clear the view by default.    //iOS 6之后不會再釋放視圖，視圖會一直保留}@end
Swift3.0的懶加載
import UIKitclass ViewController: UIViewController {    private var label : UILabel? = UILabel();        override func viewDidLoad() {        super.viewDidLoad()                label?.text = "hello";        label?.sizeToFit();                print(label!);                //釋放label        label = nil;                //和oc不同        //懶加載的代碼只會在第一次調用的時候,執行閉包，將閉包的結果保存在label的屬性中        print(label!);                    }    override func didReceiveMemoryWarning() {        super.didReceiveMemoryWarning()                //Swift中不要主動清理視圖或控件        //因為懶加載不會再次創建    }}