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*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