iOS开发UI篇—懒加载

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

 //
 //  YYViewController.m
 //  03-图片浏览器初步
 //
 //  Created by apple on 14-5-21.
 //  Copyright (c) 2014年 itcase. All rights reserved.
 //

 #import "YYViewController.h"

 #define POTOIMGW    200
 #define POTOIMGH    300
 #define POTOIMGX    60
 #define  POTOIMGY    50

 @interface YYViewController ()

 @property(nonatomic,strong)UILabel *firstlab;
 @property(nonatomic,strong)UILabel *lastlab;
 @property(nonatomic,strong)UIImageView *icon;
 @property(nonatomic,strong)UIButton *leftbtn;
 @property(nonatomic,strong)UIButton *rightbtn;
 @property(nonatomic,strong)NSArray *array;
 @property(nonatomic ,assign)int i;
 -(void)change;
 @end

 @implementation YYViewController

 - (void)viewDidLoad
 {
     [super viewDidLoad];
     [self change];
 }

 -(void)change
 {
     [self.firstlab setText:[NSString stringWithFormat:@"%d/5",self.i+]];
     //先get再set

     self.icon.image=[UIImage imageNamed:self.array[self.i][@"name"]];
     self.lastlab.text=self.array[self.i][@"desc"];

     self.leftbtn.enabled=(self.i!=);
     self.rightbtn.enabled=(self.i!=);
 }

 //延迟加载
 /**1.图片的序号标签*/
 -(UILabel *)firstlab
 {
     //判断是否已经有了，若没有，则进行实例化
     if (!_firstlab) {
         _firstlab=[[UILabel alloc]initWithFrame:CGRectMake(, , , )];
         [_firstlab setTextAlignment:NSTextAlignmentCenter];
         [self.view addSubview:_firstlab];
     }
     return _firstlab;
 }

 /**2.图片控件的延迟加载*/
 -(UIImageView *)icon
 {
      //判断是否已经有了，若没有，则进行实例化
     if (!_icon) {
         _icon=[[UIImageView alloc]initWithFrame:CGRectMake(POTOIMGX, POTOIMGY, POTOIMGW, POTOIMGH)];
         UIImage *image=[UIImage imageNamed:@"biaoqingdi"];
         _icon.image=image;
         [self.view addSubview:_icon];
     }
     return _icon;
 }

 /**3.描述控件的延迟加载*/
 -(UILabel *)lastlab
 {
      //判断是否已经有了，若没有，则进行实例化
     if (!_lastlab) {
         _lastlab=[[UILabel alloc]initWithFrame:CGRectMake(, , , )];
         [_lastlab setTextAlignment:NSTextAlignmentCenter];
         [self.view addSubview:_lastlab];
     }
     return _lastlab;
 }

 /**4.左键按钮的延迟加载*/
 -(UIButton *)leftbtn
 {
      //判断是否已经有了，若没有，则进行实例化
     if (!_leftbtn) {
         _leftbtn=[UIButton buttonWithType:UIButtonTypeCustom];
         _leftbtn.frame=CGRectMake(, self.view.center.y, , );
         [_leftbtn setBackgroundImage:[UIImage imageNamed:@"left_normal"] forState:UIControlStateNormal];
         [_leftbtn setBackgroundImage:[UIImage imageNamed:@"left_highlighted"] forState:UIControlStateHighlighted];
         [self.view addSubview:_leftbtn];
         [_leftbtn addTarget:self action:@selector(leftclick:) forControlEvents:UIControlEventTouchUpInside];
     }
     return _leftbtn;

 }

 /**5.右键按钮的延迟加载*/
 -(UIButton *)rightbtn
 {
     if (!_rightbtn) {
         _rightbtn=[UIButton buttonWithType:UIButtonTypeCustom];
         _rightbtn.frame=CGRectMake(POTOIMGX+POTOIMGW+, self.view.center.y, , );
         [_rightbtn setBackgroundImage:[UIImage imageNamed:@"right_normal"] forState:UIControlStateNormal];
         [_rightbtn setBackgroundImage:[UIImage imageNamed:@"right_highlighted"] forState:UIControlStateHighlighted];
         [self.view addSubview:_rightbtn];
         [_rightbtn addTarget:self action:@selector(rightclick:) forControlEvents:UIControlEventTouchUpInside];
     }
     return _rightbtn;
 }

 //array的get方法
 -(NSArray *)array
 {
     if (_array==nil) {
         NSString *path=[[NSBundle mainBundle] pathForResource:@"data" ofType:@"plist"];
         _array=[[NSArray alloc]initWithContentsOfFile:path];
     }
     return _array;
 }

 -(void)rightclick:(UIButton *)btn
 {
     self.i++;
     [self change];
 }

 -(void)leftclick:(UIButton *)btn
 {
     self.i--;
     [self change];
 }

 @end