解析iOS应用的UI开发中懒加载和xib的简单使用方法

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+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：

//

//  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

@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：

//

//  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

@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）

#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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