何為生成器模式？
生成器模式：將一個復雜對象的構建與它的表現分離，使得同樣的構建過程可以創建不同的表現。
生成器模式包含兩個重要的角色：Director和Builder。
Builder知道究竟如何在缺少某些特定信息的情況下建造產品。Director則知道Builde應該建造什么，以參數向其提供缺少的信息來建造特定的產品。
靜態關系如圖所示：
生成器模式.jpeg
Builder是一個抽象接口，聲明了一個BuildPart方法，該方法由ConcreteBuilder實現，以構造實際產品。ConcreteBuilder有個GetResult方法，向客戶端返回構造完畢的Product。
Direct定義了一個Construct方法，命令Builder的實例去BuildPart。Director和Builder形成了一種聚合的關系。
這意味著Builder是一個組成部分，與Director結合，以使整個模式運轉，但同時，Director并不管理Builder的生存期。
何時使用？
1.需要創建涉及各種部件的復雜對象。創建對象的算法應該獨立于部件的裝配方式。
2.構建過程需要以不同的方式構建對象。
例子：
我們將以假想的追逐游戲為例，演示如何有兩種類型的角色--敵人和游戲者。
兩種角色有一些共同的基本特征，如力量、耐力、智力、敏捷和攻擊力。每一特征都影響角色的防御與攻擊能力。防御因子反映了角色防御攻擊了的能力，而攻擊因子反映了攻擊對手的能力。
創建一個Character對象：
Charachter.h
@interface Character : NSObject
{
@private
float protection_;
float power_;
float strength_;
float stamina_;
float intelligence_;
float agility_;
float aggressiveness_;
}
@property (nonatomic, assign) float protection;
@property (nonatomic, assign) float power;
@property (nonatomic, assign) float strength;
@property (nonatomic, assign) float stamina;
@property (nonatomic, assign) float intelligence;
@property (nonatomic, assign) float agility;
@property (nonatomic, assign) float aggressiveness;
@end
//Character.m
@implementation Character
@synthesize protection = protection_;
@synthesize power=power_;
@synthesize strength=strength_;
@synthesize stamina=stamina_;
@synthesize intelligence=intelligence_;
@synthesize agility=agility_;
@synthesize aggressiveness=aggressiveness_;
- (instancetype)init{
if (self = [super init]) {
protection_ = 1.0;
power_ = 1.0;
strength_ = 1.0;
stamina_ = 1.0;
intelligence_ = 1.0;
agility_ = 1.0;
aggressiveness_ = 1.0;
}
return self;
}
@end
Character定義所有類型角色共有的一套特征。
Character只是定義了角色的共有特征，并不知道如何把自己構建成有意義的角色，所以才需要CharacterBuilder給予先前定義的特征關系，構建有意義的角色。
CharacterBuilder.h
#import "Character.h"
@interface CharacterBuilder : NSObject
{
@protected
Character * character_;
}
@property (nonatomic, strong, readonly) Character * character;
- (CharacterBuilder *) buildNewCharacter;
- (CharacterBuilder *) buildStrength:(float) value;
- (CharacterBuilder *) buildStamina:(float) value;
- (CharacterBuilder *) buildIntelligence:(float) value;
- (CharacterBuilder *) buildAgility:(float) value;
- (CharacterBuilder *) buildAggress:(float) value;
@end
CharacterBuilder.m
@implementation CharacterBuilder
@synthesize character=character_;
- (CharacterBuilder *)buildNewCharacter{
character_ = [[Character alloc] init];
return self;
}
- (CharacterBuilder *)buildStrength:(float)value{
character_.strength = value;
return self;
}
- (CharacterBuilder *)buildStamina:(float)value{
character_.stamina = value;
return self;
}
- (CharacterBuilder *)buildIntelligence:(float)value{
character_.intelligence = value;
return self;
}
- (CharacterBuilder *)buildAgility:(float)value{
character_.agility = value;
return self;
}
- (CharacterBuilder *)buildAggress:(float)value{
character_.aggressiveness = value;
return self;
}
@end
CharacterBuilder的實例有個對目標Character的引用，該目標Character構建完成后將被返回給客戶端。
StandardCharacterBuilder是CharacterBuilder的子類，定義了生成具有各種相關特征的真正角色的邏輯。
StandardCharacterBuilder.h
@interface StandardCharacterBuilder : CharacterBuilder
- (CharacterBuilder *) buildStrength:(float) value;
- (CharacterBuilder *) buildStamina:(float) value;
- (CharacterBuilder *) buildIntelligence:(float) value;
- (CharacterBuilder *) buildAgility:(float) value;
- (CharacterBuilder *) buildAggress:(float) value;
@end
再次聲明了重載的方法，是為了比較清晰。StandardCharacterBuild沒有重載buildNewCharacter方法，是因為基類的已經夠用了。
StandardCharacterBuilder.m
@implementation StandardCharacterBuilder
- (CharacterBuilder *)buildStrength:(float)value{
character_.protection *= value;
character_.power *= value;
return [super buildStrength:value];
}
- (CharacterBuilder *)buildStamina:(float)value{
character_.protection *= value;
character_.power *= value;
return [super buildStamina:value];
}
- (CharacterBuilder *)buildIntelligence:(float)value{
character_.protection *= value;
character_.power /= value;
return [super buildIntelligence:value];
}
- (CharacterBuilder *)buildAgility:(float)value{
character_.protection *= value;
character_.power /= value;
return [super buildAgility:value];
}
- (CharacterBuilder *)buildAggress:(float)value{
character_.protection /= value;
character_.power *= value;
return [super buildAggress:value];
}
@end
接下來是Director,ChasingGame類
ChasingGame.h
#import "StandardCharacterBuilder.h"
@interface ChasingGame : NSObject
- (Character *) createPlayer:(CharacterBuilder *) builder;
- (Character *) createEnemy:(CharacterBuilder *) builder;
@end
ChasingGame.m
@implementation ChasingGame
- (Character *)createPlayer:(CharacterBuilder *)builder{
[builder buildNewCharacter];
[builder buildStrength:50.0];
[builder buildStamina:25.0];
[builder buildIntelligence:75.0];
[builder buildAgility:65.0];
[builder buildAggress:35.0];
return [builder character];
}
- (Character *)createEnemy:(CharacterBuilder *)builder{
[builder buildNewCharacter];
[builder buildStrength:80.0];
[builder buildStamina:65.0];
[builder buildIntelligence:35.0];
[builder buildAgility:25.0];
[builder buildAggress:95.0];
return [builder character];
}
@end
客戶端代碼
CharacterBuilder * characterBuilder = [[StandardCharacterBuilder alloc] init];
ChasingGame * game = [[ChasingGame alloc] init];
Character * player = [game createEnemy:characterBuilder];
Character * enemy = [game createEnemy:characterBuilder];
客戶端生成StandardCharacterBuilder和ChasingGame的實例。然后向ChasingGame發送createPlayer:和createEnemy:消息。
以上就是生成器模式的具體應用。
