iOSUI基础——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

巴特西

iOSUI基础——懒加载

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