懒加载

来源:互联网 时间:2015-12-04

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+1]]; //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!=0); self.rightbtn.enabled=(self.i!=4);}

//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(20, 10, 300, 30)]; [_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(20, 400, 300, 30)]; [_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(0, self.view.center.y, 40, 40); [_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+10, self.view.center.y, 40, 40); [_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

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