iOS开发UI高级 懒加载

懒加载核心：在get方法里面进行加载，当用到时再加载而且只加载一次；

懒加载的好处：

1、就算该数据被销毁，只要程序有需要用到时，还是可以加载出来

2、使用懒加载代码可读性更高

3、对象和对象之间的独立性更强

注意：执行懒加载之前一定要先判断是否已经有了，如果没有再去进行实例化

<span style="font-size:14px;">#import "ViewController.h"@interface ViewController ()@property(nonatomic,strong)UILabel *titleLable;@property(nonatomic,strong)UIButton *loginButton;@property(nonatomic,strong)UIImageView *myImageV;@property(nonatomic,strong)NSArray *array;@property(nonatomic,assign)NSUInteger index;@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];        [self setAttributes];    }// 对属性的具体设置-(void)setAttributes{    // 初始化下标值为1    self.index = 0;    // 设置图片    [self.myImageV setImage:[UIImage imageNamed:@"1"]];    // 设置label的标题和标题颜色    self.titleLable.text = @"我是标题label";    self.titleLable.textColor = [UIColor cyanColor];        // 设置切换按钮的标题和背景颜色    [self.loginButton setTitle:@"切换图片" forState:UIControlStateNormal];    self.loginButton.backgroundColor = [UIColor orangeColor];    // 切换按钮的响应事件    [self.loginButton addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];        // 设置数组的图片数据    self.array = @[@"1",@"2",@"3",@"4",@"5",@"6",@"7"];    }//@synthesize的作用是_myImageV相当于myImageV@synthesize myImageV = _myImageV;@synthesize array = _array;// UILabel的懒加载,只调用一次-(UILabel *)titleLable{    // 先判断再执行    if (_titleLable == nil) {        _titleLable = [[UILabel alloc] initWithFrame:CGRectMake(20, 20, 200, 40)];        [self.view addSubview:_titleLable];    }    return _titleLable;}// UIButton的懒加载,只调用一次-(UIButton *)loginButton{        // 先判断再执行    if (_loginButton == nil) {        _loginButton = [UIButton buttonWithType:UIButtonTypeCustom];        _loginButton.frame = CGRectMake(0, 0, 200, 30);        _loginButton.center = CGPointMake(self.view.bounds.size.width*0.5, self.view.bounds.size.height*0.5);                [self.view addSubview:_loginButton];    }    return _loginButton;}// UIImageView的懒加载，只调用一次-(UIImageView *)myImageV{    // 先判断    if (_myImageV == nil) {        _myImageV = [[UIImageView alloc] initWithFrame:CGRectMake(60, 50, 300, 300)];        [self.view addSubview:_myImageV];    }    return _myImageV;}//NSArray的懒加载，只加载一次-(NSArray *)array{    // 先判断    if (_array == nil) {        _array = [NSArray array];    }    return _array;}#pragma mark - 切换按钮的响应事件-(void)buttonAction:(UIButton *)button {        self.index++;    // 如果切换到最后一张图片，返回第一张    if (self.index > 6) {        self.index = 0;    }    // 重新设置self.myImageV,实现图片切换    [self.myImageV setImage:[UIImage imageNamed:self.array[self.index]]];    }- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}@end</span>