【移動應用開發(fā)技術】iOS中如何創(chuàng)建Model

【移動應用開發(fā)技術】iOS中如何創(chuàng)建Model

在下給大家分享一下iOS中如何創(chuàng)建Model，相信大部分人都還不怎么了解，因此分享這篇文章給大家參考一下，希望大家閱讀完這篇文章后大有收獲，下面讓我們一起去了解一下吧！ImmutableModel我們以UserModle為例，我們可以像這樣創(chuàng)建：public

class

UserModel:

NSObject

{

public

var

userId:

NSNumber

public

var

name:

String?

public

var

email:

String?

public

var

age:

Int?

public

var

address:

String?

init(userId:

NSNumber)

{

self.userId

=

userId

super.init()

}

}用的時候可以像這樣：let

userModel

=

UserModel(userId:

1)

user.email

=

"335050309@"

=

"roy"

user.age

=

27

user.address

=

"上海市楊浦區(qū)"這樣創(chuàng)建一個User對象好處是彈性很大，我可以隨意選擇設定某個property的值，但是背后同樣帶有很大的缺點，就是這個Model變得異常開放，不安分，這種Model我們一般叫MutableModel。有的時候我們需要MutableModel，但大部分的時候出于數(shù)據(jù)安全和解耦考慮我們不希望創(chuàng)建的property在外部可以隨意改變，在初始化后不可變的Model叫做ImmutableModel，在開發(fā)中我的建議盡量使用ImmutableModel。我們通過把property設置成readonly，在Swift可以用let或者private(set)。也就是這樣：public

class

UserModel:

NSObject

{

public

let

userId:

NSNumber

public

private(set)

var

name:

String?

public

private(set)

var

email:

String?

public

private(set)

var

age:

Int?

public

private(set)

var

address:

String?

}那么怎么寫初始化方法呢？Initializermappingargumentstoproperties當我們把property設置成readonly后，我們只能在init的時候賦值，這個時候就變成這樣：public

class

User:

NSObject

{

public

var

userId:

NSNumber

public

var

name:

String?

public

var

email:

String?

public

var

age:

Int?

public

var

address:

String?

init(userId:

NSNumber,

name:

String?,

email:

String,

age:

Int,

address:

String)

{

self.userId

=

userId

super.init()

=

name

self.email

=

email

self.age

=

age

self.address

=

address

}

}使用的時候就變成這樣：let

user

=

User.init(userId:

1,

name:

"335050309@",

email:

"roy",

age:

27,

address:

"上海市楊浦區(qū)")這樣創(chuàng)建Model安全可靠，大多數(shù)時候是有效的，但是也有一些缺點：如果property很多，init方法就有很多形參，然后變得又臭又長。有的時候我們只需要Model的某些property，這樣我們可能為各個不同的需求寫不同的init方法，最終讓UserModel變得很龐大。Initializertakingdictionary初始化的時候注入一個字典，就是下面的樣子：public

class

UserModel:

NSObject

{

public

let

userId:

NSNumber

public

private(set)

var

name:

String?

public

private(set)

var

email:

String?

public

private(set)

var

age:

Int?

public

private(set)

var

address:

String?

init(dic:

NSDictionary)

{

self.userId

=

(dic["userId"]

as?

NSNumber)!

super.init()

=

dic["name"]

as?

String

self.email

=

dic["email"]

as?

String

self.age

=

dic["age"]

as?

Int

self.address

=

dic["address"]

as?

String

}

}很顯然這解決上一種第一個缺點，但是還是有一個不足之處：如果字典沒有某個屬性對應的key的時候會崩潰，編譯器并不能幫助我們排查這種運行時的崩潰。不能很好的滿足某些時候只需要Model的某些property的需求。Mutablesubclass我們看看ImprovingImmutableObjectInitializationinObjective-C關于這個是怎么描述的Weendupunsatisfiedandcontinueourquestforthebestwaytoinitializeimmutableobjects.Cocoaisavastland,sowecan–andshould–stealsomeoftheideasusedbyAppleinitsframeworks.WecancreateamutablesubclassofReminderclasswhichredefinesallpropertiesasreadwrite:Weendupunsatisfiedandcontinueourquestforthebestwaytoinitializeimmutableobjects.Cocoaisavastland,sowecan–andshould–stealsomeoftheideasusedbyAppleinitsframeworks.WecancreateamutablesubclassofReminderclasswhichredefinesallpropertiesasreadwrite:@interface

MutableReminder

:

Reminder

<NSCopying,

NSMutableCopying>

@property

(nonatomic,

copy,

readwrite)

NSString

*title;

@property

(nonatomic,

strong,

readwrite)

NSDate

*date;

@property

(nonatomic,

assign,

readwrite)

BOOL

showsAlert;

@endAppleusesthisapproachforexampleinNSParagraphStyleandNSMutableParagraphStyle.Wemovebetweenmutableandimmutablecounterpartswith-copyand-mutableCopy.Themostcommoncasematchesourexample:abaseclassisimmutableanditssubclassismutable.AppleusesthisapproachforexampleinNSParagraphStyleandNSMutableParagraphStyle.Wemovebetweenmutableandimmutablecounterpartswith-copyand-mutableCopy.Themostcommoncasematchesourexample:abaseclassisimmutableanditssubclassismutable.Themaindisadvantageofthiswayisthatweendupwithtwiceasmanyclasses.What'smore,mutablesubclassesoftenexistonlyasawaytoinitializeandmodifytheirimmutableversions.Manybugscanbecausedbyusingamutablesubclassbyaccident.Forexample,amentalburdenshowsinsettingupproperties.Wehavetoalwayscheckifamutablesubclassexists,andifsousecopymodifierinsteadofstrongforthebaseclass.Themaindisadvantageofthiswayisthatweendupwithtwiceasmanyclasses.What'smore,mutablesubclassesoftenexistonlyasawaytoinitializeandmodifytheirimmutableversions.Manybugscanbecausedbyusingamutablesubclassbyaccident.Forexample,amentalburdenshowsinsettingupproperties.Wehavetoalwayscheckifamutablesubclassexists,andifsousecopymodifierinsteadofstrongforthebaseclass.大致意思是創(chuàng)建一個可變子類，它將所有屬性重新定義為readwrite。這種方式的主要缺點是我們最終得到兩倍的類。而且，可變子類通常僅作為初始化和修改其不可變版本的方式存在。偶然使用可變子類可能會導致許多錯誤。例如，在設置屬性時會出現(xiàn)心理負擔。我們必須始終檢查是否存在可變子類。還有一點這種方式只能在Objective-C中使用。BuilderpatternBuilderpattern模式需要我們使用一個Builder來創(chuàng)建目標對象，目標對象的property依舊是readonly，但是Builder的對應property卻可以選擇為readwrite。依舊用UserModel為例，我們需要為其進行適當?shù)母脑?，改造之后：typealias

UserModelBuilderBlock

=

(UserModelBuilder)

->

UserModelBuilder

public

class

UserModel:

NSObject{

public

let

userId:

NSNumber

public

private(set)

var

name:

String?

public

private(set)

var

email:

String?

public

private(set)

var

age:

Int?

public

private(set)

var

address:

String?

init(userId:

NSNumber)

{

self.userId

=

userId

super.init()

}

convenience

init(userId:

NSNumber

,with

block:

UserModelBuilderBlock){

let

userModelBuilder

=

block(UserModelBuilder.init(userId:

userId))

self.init(userId:

userModelBuilder.userId)

self.email

=

userModelBuilder.email

=

userModelB

self.age

=

userModelBuilder.age

self.address

=

userModelBuilder.address

}

}之后是對應的Builderclass

UserModelBuilder:

NSObject

{

public

let

userId:

NSNumber

public

var

name:

String?

public

var

email:

String?

public

var

age:

Int?

public

var

address:

String?

init(userId:

NSNumber)

{

self.userId

=

userId

super.init()

}

}然后可以像下面這樣使用：let

userModle

=

UserModel(userId:

1)

{

(builder)

->

UserModelBuilder

in

builder.email

=

"335050309@"

=

"roy"

builder.age

=

27

builder.address

=

"上海市楊浦區(qū)"

return

builder

}這種方式雖然我們需要為Model再創(chuàng)建一個Builder，略顯啰嗦和復雜，但是當property較多，對Model的需求又比較復雜的時候這又確實是一種值得推薦的方式。以上全是Swift的代碼實現(xiàn)，下面我再貼上對應的OC代碼#import

<Foundation/Foundation.h>

@interface

RUserModelBuilder

:

NSObject

@property

(nonatomic,

strong,

readwrite,

nonnull)

NSNumber

*userId;

@property

(nonatomic,

copy,

readwrite,

nullable)

NSString

*name;

@property

(nonatomic,

copy,

readwrite,

nullable)

NSString

*email;

@property

(nonatomic,

copy,

readwrite,

nullable)

NSNumber

*age;

@property

(nonatomic,

copy,

readwrite,

nullable)

NSString

*address;

@end

typedef

RUserModelBuilder

*__nonnull(^RUserModelBuilderBlock)(RUserModelBuilder

*__nonnull

userModelBuilder);

@interface

RUserModel

:

NSObject

@property

(nonatomic,

strong,

readonly,

nonnull)

NSNumber

*userId;

@property

(nonatomic,

copy,

readonly,

nullable)

NSString

*name;

@property

(nonatomic,

copy,

readonly,

nullable)

NSString

*email;

@property

(nonatomic,

copy,

readonly,

nullable)

NSNumber

*age;

@property

(nonatomic,

copy,

readonly,

nullable)

NSString

*address;

+

(nonnull

instancetype)buildWithBlock:(nonnull

RUserModelBuilderBlock)builderBlock;

@end#import

"RUserModel.h"

@implementation

RUserModelBuilder

@end

@interface

RUserModel

()

@property

(nonatomic,

strong