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懶加載

1.懶加載根本

懶加載——也稱為延遲加載，即在須要的時刻才加載（效力低，占用內存小）。所謂懶加載，寫的是其get辦法.

留意：假如是懶加載的話則必定要留意先斷定能否曾經有了，假如沒有那末再去停止實例化

2.應用懶加載的利益：

（1）不用將創立對象的代碼全體寫在viewDidLoad辦法中，代碼的可讀性更強

（2）每一個控件的getter辦法平分別擔任各自的實例化處置，代碼彼此之間的自力性強，松耦合

3.代碼示例

//
//  YYViewController.m
//  03-圖片閱讀器初步
//
//  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);
}

//延遲加載
/**1.圖片的序號標簽*/
-(UILabel *)firstlab
{
    //斷定能否曾經有了，若沒有，則停止實例化
    if (!_firstlab) {
        _firstlab=[[UILabel alloc]initWithFrame:CGRectMake(20, 10, 300, 30)];
        [_firstlab setTextAlignment:NSTextAlignmentCenter];
        [self.view addSubview:_firstlab];
    }
    return _firstlab;
}

/**2.圖片控件的延遲加載*/
-(UIImageView *)icon
{
     //斷定能否曾經有了，若沒有，則停止實例化
    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.描寫控件的延遲加載*/
-(UILabel *)lastlab
{
     //斷定能否曾經有了，若沒有，則停止實例化
    if (!_lastlab) {
        _lastlab=[[UILabel alloc]initWithFrame:CGRectMake(20, 400, 300, 30)];
        [_lastlab setTextAlignment:NSTextAlignmentCenter];
        [self.view addSubview:_lastlab];
    }
    return _lastlab;
}

/**4.左鍵按鈕的延遲加載*/
-(UIButton *)leftbtn
{
     //斷定能否曾經有了，若沒有，則停止實例化
    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.右鍵按鈕的延遲加載*/
-(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辦法
-(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的簡略應用
1、簡略引見

xib和storyboard的比擬，一個輕量級一個分量級。

配合點：

都用來描寫軟件界面

都用Interface Builder對象來編纂

分歧點:

Xib是輕量級的，用來描寫部分的UI界面

Storyboard是分量級的，用來描寫全部軟件的多個界面，而且能展現多個界面之間的跳轉關系

2、xib的簡略應用

1.樹立xib文件

樹立的xib文件定名為appxib.xib

2.對xib停止設置

　　依據法式的須要，這裡把view調劑為自在結構

樹立view模子（設置長寬等參數）

調劑結構和外部的控件

完成後的單個view

3.應用xib文件的代碼示例

YYViewController.m文件代碼以下：

//
//  YYViewController.m
//  10-xib文件的應用
//
//  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


@implementation YYViewController

//1.加載數據信息
-(NSArray *)app
{
    if (!_app) {
        NSString *path=[[NSBundle mainBundle]pathForResource:@"app.plist" ofType:nil];
        NSArray *temparray=[NSArray arrayWithContentsOfFile:path];
       
        //字典轉模子
        NSMutableArray *arrayM=[NSMutableArray array ];
        for (NSDictionary *dict in temparray) {
            [arrayM addObject:[YYapp appWithDict:dict]];
        }
        _app=arrayM;
    }
    return _app;
}

//創立界面原型
- (void)viewDidLoad
{
    [super viewDidLoad];
    NSLog(@"%d",self.app.count);
   
    //九宮格結構
    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視圖
       NSArray  *apparray= [[NSBundle mainBundle]loadNibNamed:@"appxib" owner:nil options:nil];
        UIView *appview=[apparray firstObject];
        //加載視圖
        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];
    }
}

/**按鈕的點擊事宜*/
-(void)appviewbtnClick:(UIButton *)btn
{
    YYapp *apps=self.app[btn.tag];
    UILabel *showlab=[[UILabel alloc]initWithFrame:CGRectMake(60, 450, 200, 20)];
    [showlab setText:[NSString stringWithFormat: @"%@下載勝利",apps.name]];
    [showlab setBackgroundColor:[UIColor lightGrayColor]];
    [self.view addSubview:showlab];
    showlab.alpha=1.0;
   
    //簡略的動畫後果
    [UIView animateWithDuration:2.0 animations:^{
        showlab.alpha=0;
    } completion:^(BOOL finished) {
        [showlab removeFromSuperview];
    }];
}

@end

運轉後果：

3、對xib停止連線示例

1.連線示例

新建一個xib對應的視圖類，繼續自Uiview

在xib界面右上角與新建的視圖類停止聯系關系

把xib和視圖類停止連線

留意：在應用中把weak改成為強援用。不然...

2.連線後的代碼示例

YYViewController.m文件代碼以下：

//
//  YYViewController.m
//  10-xib文件的應用
//
//  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


@implementation YYViewController

//1.加載數據信息
-(NSArray *)app
{
    if (!_app) {
        NSString *path=[[NSBundle mainBundle]pathForResource:@"app.plist" ofType:nil];
        NSArray *temparray=[NSArray arrayWithContentsOfFile:path];
       
        //字典轉模子
        NSMutableArray *arrayM=[NSMutableArray array ];
        for (NSDictionary *dict in temparray) {
            [arrayM addObject:[YYapp appWithDict:dict]];
        }
        _app=arrayM;
    }
    return _app;
}

//創立界面原型
- (void)viewDidLoad
{
    [super viewDidLoad];
    NSLog(@"%d",self.app.count);
   
    //九宮格結構
    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視圖
       NSArray  *apparray= [[NSBundle mainBundle]loadNibNamed:@"appxib" owner:nil options:nil];
       
        //留意這裡的類型名!
        //UIView *appview=[apparray firstObject];
        YYappview  *appview=[apparray firstObject];
      
        //加載視圖
        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];
      
    }
}

/**按鈕的點擊事宜*/
-(void)appviewbtnClick:(UIButton *)btn
{
    YYapp *apps=self.app[btn.tag];
    UILabel *showlab=[[UILabel alloc]initWithFrame:CGRectMake(60, 450, 200, 20)];
    [showlab setText:[NSString stringWithFormat: @"%@下載勝利",apps.name]];
    [showlab setBackgroundColor:[UIColor lightGrayColor]];
    [self.view addSubview:showlab];
    showlab.alpha=1.0;
   
    //簡略的動畫後果
    [UIView animateWithDuration:2.0 animations:^{
        showlab.alpha=0;
    } completion:^(BOOL finished) {
        [showlab removeFromSuperview];
    }];
}

@end

YYappview.h文件代碼（曾經連線）

#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

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