iOS開發UI篇—懶載入

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.懶載入基本

懶載入——也稱為消極式載入，即在需要的時候才載入（效率低，佔用記憶體小）。所謂懶載入，寫的是其get方法.

注意：如果是懶載入的話則一定要注意先判斷是否已經有了，如果沒有那麼再去進行執行個體化

2.使用懶載入的好處：

（1）不必將建立對象的代碼全部寫在viewDidLoad方法中，代碼的可讀性更強

（2）每個控制項的getter方法中分別負責各自的執行個體化處理，代碼彼此之間的獨立性強，松耦合

3.程式碼範例

1 //  2 //  YYViewController.m  3 //  03-圖片瀏覽器初步  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    20012 #define POTOIMGH    30013 #define POTOIMGX    6014 #define  POTOIMGY    5015 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 @end27 28 29 30 @implementation YYViewController31 32 - (void)viewDidLoad33 {34     [super viewDidLoad];35     [self change];36 }37 38 -(void)change39 {40     [self.firstlab setText:[NSString stringWithFormat:@"%d/5",self.i+1]];41     //先get再set42     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 //消極式載入51 /**1.圖片的序號標籤*/52 -(UILabel *)firstlab53 {54     //判斷是否已經有了，若沒有，則進行執行個體化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.圖片控制項的消極式載入*/64 -(UIImageView *)icon65 {66      //判斷是否已經有了，若沒有，則進行執行個體化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.描述控制項的消極式載入*/77 -(UILabel *)lastlab78 {79      //判斷是否已經有了，若沒有，則進行執行個體化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.左鍵按鈕的消極式載入*/89 -(UIButton *)leftbtn90 {91      //判斷是否已經有了，若沒有，則進行執行個體化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.右鍵按鈕的消極式載入*/105 -(UIButton *)rightbtn106 {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 *)array120 {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 *)btn129 {130     self.i++;131     [self change];132 }133 134 -(void)leftclick:(UIButton *)btn135 {136     self.i--;137     [self change];138 }139 140 @end 

 

iOS開發UI篇—懶載入