iOS开发UI篇—懒加载
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
3.代码示例
1 // 2 // YYViewController.m 3 // 03-图片浏览器初步 4 // 5 // Created by apple on 14-5-21. 6 // Copyright (c) 2014年 itcase. All rights reserved. 7 // 8 9 #import "YYViewController.h" 10 11 #define POTOIMGW 200 12 #define POTOIMGH 300 13 #define POTOIMGX 60 14 #define POTOIMGY 50 15 16 @interface YYViewController () 17 18 @property(nonatomic,strong)UILabel *firstlab; 19 @property(nonatomic,strong)UILabel *lastlab; 20 @property(nonatomic,strong)UIImageView *icon; 21 @property(nonatomic,strong)UIButton *leftbtn; 22 @property(nonatomic,strong)UIButton *rightbtn; 23 @property(nonatomic,strong)NSArray *array; 24 @property(nonatomic ,assign)int i; 25 -(void)change; 26 @end 27 28 29 30 @implementation YYViewController 31 32 - (void)viewDidLoad 33 { 34 [super viewDidLoad]; 35 [self change]; 36 } 37 38 -(void)change 39 { 40 [self.firstlab setText:[NSString stringWithFormat:@"%d/5",self.i+1]]; 41 //先get再set 42 43 self.icon.image=[UIImage imageNamed:self.array[self.i][@"name"]]; 44 self.lastlab.text=self.array[self.i][@"desc"]; 45 46 self.leftbtn.enabled=(self.i!=0); 47 self.rightbtn.enabled=(self.i!=4); 48 } 49 50 //延迟加载 51 /**1.图片的序号标签*/ 52 -(UILabel *)firstlab 53 { 54 //判断是否已经有了，若没有，则进行实例化 55 if (!_firstlab) { 56 _firstlab=[[UILabel alloc]initWithFrame:CGRectMake(20, 10, 300, 30)]; 57 [_firstlab setTextAlignment:NSTextAlignmentCenter]; 58 [self.view addSubview:_firstlab]; 59 } 60 return _firstlab; 61 } 62 63 /**2.图片控件的延迟加载*/ 64 -(UIImageView *)icon 65 { 66 //判断是否已经有了，若没有，则进行实例化 67 if (!_icon) { 68 _icon=[[UIImageView alloc]initWithFrame:CGRectMake(POTOIMGX, POTOIMGY, POTOIMGW, POTOIMGH)]; 69 UIImage *image=[UIImage imageNamed:@"biaoqingdi"]; 70 _icon.image=image; 71 [self.view addSubview:_icon]; 72 } 73 return _icon; 74 } 75 76 /**3.描述控件的延迟加载*/ 77 -(UILabel *)lastlab 78 { 79 //判断是否已经有了，若没有，则进行实例化 80 if (!_lastlab) { 81 _lastlab=[[UILabel alloc]initWithFrame:CGRectMake(20, 400, 300, 30)]; 82 [_lastlab setTextAlignment:NSTextAlignmentCenter]; 83 [self.view addSubview:_lastlab]; 84 } 85 return _lastlab; 86 } 87 88 /**4.左键按钮的延迟加载*/ 89 -(UIButton *)leftbtn 90 { 91 //判断是否已经有了，若没有，则进行实例化 92 if (!_leftbtn) { 93 _leftbtn=[UIButton buttonWithType:UIButtonTypeCustom]; 94 _leftbtn.frame=CGRectMake(0, self.view.center.y, 40, 40); 95 [_leftbtn setBackgroundImage:[UIImage imageNamed:@"left_normal"] forState:UIControlStateNormal]; 96 [_leftbtn setBackgroundImage:[UIImage imageNamed:@"left_highlighted"] forState:UIControlStateHighlighted]; 97 [self.view addSubview:_leftbtn]; 98 [_leftbtn addTarget:self action:@selector(leftclick:) forControlEvents:UIControlEventTouchUpInside]; 99 } 100 return _leftbtn; 101 102 } 103 104 /**5.右键按钮的延迟加载*/ 105 -(UIButton *)rightbtn 106 { 107 if (!_rightbtn) { 108 _rightbtn=[UIButton buttonWithType:UIButtonTypeCustom]; 109 _rightbtn.frame=CGRectMake(POTOIMGX+POTOIMGW+10, self.view.center.y, 40, 40); 110 [_rightbtn setBackgroundImage:[UIImage imageNamed:@"right_normal"] forState:UIControlStateNormal]; 111 [_rightbtn setBackgroundImage:[UIImage imageNamed:@"right_highlighted"] forState:UIControlStateHighlighted]; 112 [self.view addSubview:_rightbtn]; 113 [_rightbtn addTarget:self action:@selector(rightclick:) forControlEvents:UIControlEventTouchUpInside]; 114 } 115 return _rightbtn; 116 } 117 118 //array的get方法 119 -(NSArray *)array 120 { 121 if (_array==nil) { 122 NSString *path=[[NSBundle mainBundle] pathForResource:@"data" ofType:@"plist"]; 123 _array=[[NSArray alloc]initWithContentsOfFile:path]; 124 } 125 return _array; 126 } 127 128 -(void)rightclick:(UIButton *)btn 129 { 130 self.i++; 131 [self change]; 132 } 133 134 -(void)leftclick:(UIButton *)btn 135 { 136 self.i--; 137 [self change]; 138 } 139 140 @end