前言
作為一個優秀的程序員，或者想成為優秀的程序員，最基本的你得有MVC編程思想，那么你就要對JSON獲取的數據建Model，將service和controller層都分離，從而做到低耦合。現在有很多利用runtime能快速的將json數據轉為一個Model。但是我在做項目的時候，發現創建Model(特別是屬性特多的)寫屬性代碼很浪費時間，降低了編程效率。后來我自己就寫了個好玩的能省去時間創建Model的一個方法，下面話不多說了，來一起看看詳細的介紹吧
Immutable Model
我們以UserModle為例，我們可以像這樣創建：
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@qq.com"user.name = "roy"user.age = 27user.address = "上海市楊浦區"
這樣創建一個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Mutable Model。有的時候我們需要Mutable Model，但大部分的時候出于數據安全和解耦考慮我們不希望創建的property在外部可以隨意改變，在初始化后不可變的Model叫做Immutable Model，在開發中我的建議盡量使用Immutable Model。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？
Initializer mapping arguments to properties
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() self.name = 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@qq.com", email: "roy", age: 27, address: "上海市楊浦區")
這樣創建Model安全可靠，大多數時候是有效的，但是也有一些缺點：
Initializer taking dictionary
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() self.name = 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：
Mutable subclass
我們看看Improving Immutable Object Initialization in Objective-C關于這個是怎么描述的
We end up unsatisfied and continue our quest for the best way to initialize immutable objects. Cocoa is a vast land, so we can – and should – steal some of the ideas used by Apple in its frameworks. We can create a mutable subclass of Reminder class which redefines all properties as readwrite:
@interface MutableReminder : Reminder <NSCopying, NSMutableCopying>@property (nonatomic, copy, readwrite) NSString *title;@property (nonatomic, strong, readwrite) NSDate *date;@property (nonatomic, assign, readwrite) BOOL showsAlert;@end
Apple uses this approach for example in NSParagraphStyle and NSMutableParagraphStyle. We move between mutable and immutable counterparts with -copy and -mutableCopy. The most common case matches our example: a base class is immutable and its subclass is mutable.
The main disadvantage of this way is that we end up with twice as many classes. What's more, mutable subclasses often exist only as a way to initialize and modify their immutable versions. Many bugs can be caused by using a mutable subclass by accident. For example, a mental burden shows in setting up properties. We have to always check if a mutable subclass exists, and if so use copy modifier instead of strong for the base class.
大致意思是創建一個可變子類，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。
Builder pattern
Builder pattern 模式需要我們使用一個Builder來創建目標對象，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的改造，改造之后：
typealias UserModelBuilderBlock = (UserModelBuilder) -> UserModelBuilderpublic 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 self.name = userModelBuilder.name self.age = userModelBuilder.age self.address = userModelBuilder.address }}之后是對應的Builder
class 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@qq.com" builder.name = "roy" builder.age = 27 builder.address = "上海市楊浦區" return builder}這種方式雖然我們需要為Model再創建一個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，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;@endtypedef 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, 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@implementation RUserModel#pragma mark - NSCopying+ (nonnull instancetype)buildWithBlock:(nonnull RUserModelBuilderBlock)builderBlock { RUserModelBuilder *userModelBuilder = builderBlock([[RUserModelBuilder alloc] init]); RUserModel *userModel = [[RUserModel alloc] init]; userModel.userId = userModelBuilder.userId; userModel.name = userModelBuilder.name; userModel.email = userModelBuilder.email; userModel.age = userModelBuilder.age; userModel.address = userModelBuilder.address; return userModel;}@enddemo地址：ImmutableModel
參考文章：
Improving Immutable Object Initialization in Objective-C
總結
以上就是這篇文章的全部內容了，希望本文的內容對大家的學習或者工作具有一定的參考學習價值，如果有疑問大家可以留言交流，謝謝大家對VEVB武林網的支持。
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