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
复制代码 代码如下:
//
//  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

复制代码 代码如下:
@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

xib的简单使用
一、简单介绍

xib和storyboard的比较，一个轻量级一个重量级。

共同点：

都用来描述软件界面

都用Interface Builder工具来编辑

不同点:

Xib是轻量级的，用来描述局部的UI界面

Storyboard是重量级的，用来描述整个软件的多个界面，并且能展示多个界面之间的跳转关系

二、xib的简单使用

1.建立xib文件

建立的xib文件命名为appxib.xib

2.对xib进行设置

　　根据程序的需要，这里把view调整为自由布局

建立view模型（设置长宽等参数）

调整布局和内部的控件

完成后的单个view

3.使用xib文件的代码示例

YYViewController.m文件代码如下：
复制代码 代码如下:
//
//  YYViewController.m
//  10-xib文件的使用
//
//  Created by apple on 14-5-24.
//  Copyright (c) 2014年 itcase. All rights reserved.
//

#import "YYViewController.h"
#import "YYapp.h"

@interface YYViewController ()
@property(nonatomic,strong)NSArray *app;
@end

复制代码 代码如下:
@implementation YYViewController

//1.加载数据信息
-(NSArray *)app
{
    if (!_app) {
        NSString *path=[[NSBundle mainBundle]pathForResource:@"app.plist" ofType:nil];
        NSArray *temparray=[NSArray arrayWithContentsOfFile:path];
       
        //字典转模型
        NSMutableArray *arrayM=[NSMutableArray array ];
        for (NSDictionary *dict in temparray) {
            [arrayM addObject:[YYapp appWithDict:dict]];
        }
        _app=arrayM;
    }
    return _app;
}

//创建界面原型
- (void)viewDidLoad
{
    [super viewDidLoad];
    NSLog(@"%d",self.app.count);
   
    //九宫格布局
    int totalloc=3;
    CGFloat appviewW=80;
    CGFloat appviewH=90;
    CGFloat margin=(self.view.frame.size.width-totalloc*appviewW)/(totalloc+1);
   
    int count=self.app.count;
    for (int i=0; i<count; i++) {
       
        int row=i/totalloc;
        int loc=i%totalloc;
        CGFloat appviewX=margin + (margin +appviewW)*loc;
        CGFloat appviewY=margin + (margin +appviewH)*row;
        YYapp *app=self.app[i];
       
        //拿出xib视图
       NSArray  *apparray= [[NSBundle mainBundle]loadNibNamed:@"appxib" owner:nil options:nil];
        UIView *appview=[apparray firstObject];
        //加载视图
        appview.frame=CGRectMake(appviewX, appviewY, appviewW, appviewH);
       
        UIImageView *appviewImg=(UIImageView *)[appview viewWithTag:1];
        appviewImg.image=app.image;
       
        UILabel *appviewlab=(UILabel *)[appview viewWithTag:2];
        appviewlab.text=app.name;
       
        UIButton *appviewbtn=(UIButton *)[appview viewWithTag:3];
        [appviewbtn addTarget:self action:@selector(appviewbtnClick:) forControlEvents:UIControlEventTouchUpInside];
        appviewbtn.tag=i;
       
        [self.view addSubview:appview];
    }
}

/**按钮的点击事件*/
-(void)appviewbtnClick:(UIButton *)btn
{
    YYapp *apps=self.app[btn.tag];
    UILabel *showlab=[[UILabel alloc]initWithFrame:CGRectMake(60, 450, 200, 20)];
    [showlab setText:[NSString stringWithFormat: @"%@下载成功",apps.name]];
    [showlab setBackgroundColor:[UIColor lightGrayColor]];
    [self.view addSubview:showlab];
    showlab.alpha=1.0;
   
    //简单的动画效果
    [UIView animateWithDuration:2.0 animations:^{
        showlab.alpha=0;
    } completion:^(BOOL finished) {
        [showlab removeFromSuperview];
    }];
}

@end

运行效果：

三、对xib进行连线示例

1.连线示例

新建一个xib对应的视图类，继承自Uiview

在xib界面右上角与新建的视图类进行关联

把xib和视图类进行连线

注意：在使用中把weak改成为强引用。否则...

2.连线后的代码示例

YYViewController.m文件代码如下：
复制代码 代码如下:
//
//  YYViewController.m
//  10-xib文件的使用
//
//  Created by apple on 14-5-24.
//  Copyright (c) 2014年 itcase. All rights reserved.
//

#import "YYViewController.h"
#import "YYapp.h"
#import "YYappview.h"

@interface YYViewController ()
@property(nonatomic,strong)NSArray *app;
@end

复制代码 代码如下:
@implementation YYViewController

//1.加载数据信息
-(NSArray *)app
{
    if (!_app) {
        NSString *path=[[NSBundle mainBundle]pathForResource:@"app.plist" ofType:nil];
        NSArray *temparray=[NSArray arrayWithContentsOfFile:path];
       
        //字典转模型
        NSMutableArray *arrayM=[NSMutableArray array ];
        for (NSDictionary *dict in temparray) {
            [arrayM addObject:[YYapp appWithDict:dict]];
        }
        _app=arrayM;
    }
    return _app;
}

//创建界面原型
- (void)viewDidLoad
{
    [super viewDidLoad];
    NSLog(@"%d",self.app.count);
   
    //九宫格布局
    int totalloc=3;
    CGFloat appviewW=80;
    CGFloat appviewH=90;
    CGFloat margin=(self.view.frame.size.width-totalloc*appviewW)/(totalloc+1);
   
    int count=self.app.count;
    for (int i=0; i<count; i++) {
       
        int row=i/totalloc;
        int loc=i%totalloc;
        CGFloat appviewX=margin + (margin +appviewW)*loc;
        CGFloat appviewY=margin + (margin +appviewH)*row;
        YYapp *app=self.app[i];
       
        //拿出xib视图
       NSArray  *apparray= [[NSBundle mainBundle]loadNibNamed:@"appxib" owner:nil options:nil];
       
        //注意这里的类型名!
        //UIView *appview=[apparray firstObject];
        YYappview  *appview=[apparray firstObject];
      
        //加载视图
        appview.frame=CGRectMake(appviewX, appviewY, appviewW, appviewH);
          [self.view addSubview:appview];
       
        appview.appimg.image=app.image;
        appview.applab.text=app.name;
        appview.appbtn.tag=i;
       
        [ appview.appbtn addTarget:self action:@selector(appviewbtnClick:) forControlEvents:UIControlEventTouchUpInside];
      
    }
}

/**按钮的点击事件*/
-(void)appviewbtnClick:(UIButton *)btn
{
    YYapp *apps=self.app[btn.tag];
    UILabel *showlab=[[UILabel alloc]initWithFrame:CGRectMake(60, 450, 200, 20)];
    [showlab setText:[NSString stringWithFormat: @"%@下载成功",apps.name]];
    [showlab setBackgroundColor:[UIColor lightGrayColor]];
    [self.view addSubview:showlab];
    showlab.alpha=1.0;
   
    //简单的动画效果
    [UIView animateWithDuration:2.0 animations:^{
        showlab.alpha=0;
    } completion:^(BOOL finished) {
        [showlab removeFromSuperview];
    }];
}

@end

YYappview.h文件代码（已经连线）
复制代码 代码如下:
#import <UIKit/UIKit.h>

@interface YYappview : UIView
@property (strong, nonatomic) IBOutlet UIImageView *appimg;
@property (strong, nonatomic) IBOutlet UILabel *applab;
@property (strong, nonatomic) IBOutlet UIButton *appbtn;
@end