概述

其核心思想是將一個“複雜物件的構建演算法”與它的“部件及組裝方式”分離，使得構件演算法和組裝方式可以獨立應對變化；複用同樣的構建演算法可以建立不同的表示，不同的構建過程可以複用相同的部件組裝方式。

主要優缺點

在建立者模式中，客戶端不再負責物件的建立與組裝，而是把這個物件建立的責任交給其具體的建立者類，把組裝的責任交給組裝類，客戶端只負責物件的呼叫，從而明確了各個類的職責。
雖然利用建立者模式可以創建出不同型別的產品，但是如果產品之間的差異巨大，則需要編寫多個建立者類才能實現，如果這是結合工廠模式更好。

建立者模式主要由五個部分構成：組裝類，抽象建立者類，實現抽象建立者類的具體建立者類，抽象產品和實現抽象產品的具體產品類。

UML圖

時序圖

程式碼示例：

建立構建者協議類Builder

#import <Foundation/Foundation.h>

// 構建者
@protocol Builder <NSObject>

// 構建部分
- (NSString *)builderPart;
@end

建立具體生成者類ConcreteBuild
ConcreteBuild.h

#import <Foundation/Foundation.h>
#import "Builder.h"

@interface ConcreteBuild : NSObject
 
 <Builder>

@end

ConcreteBuild.m

#import "ConcreteBuild.h"

@implementation ConcreteBuild

#pragma mark - Builder
- (NSString *)builderPart {
    return @"實現協議, 返回產品";
}
@end

建立組裝者類Director

Director.h

#import <Foundation/Foundation.h>
#import "Builder.h"

@interface Director : NSObject
 


// 建立傳入的實現者
- (instancetype)initWithBuilder:(id<Builder>)builder;

// 建造
- (NSString *)construct;
@end

Director.m

#import "Director.h"

@interface Director ()
@property (nonatomic, copy) id<Builder> builder;
@end

@implementation Director
- (instancetype)initWithBuilder:(id<Builder>)builder {
    self = [super init];
    if (self) {
        _builder = builder;
    }
    return self;
}

// 建造
- (NSString *)construct {
    // 建立部件
    return [self.builder builderPart];
}
@end

ViewController呼叫

#import "ViewController.h"
#import "Director.h"
#import "ConcreteBuild.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    // 1.建立生成者, 知道要做的產品
    ConcreteBuild *build = [[ConcreteBuild alloc] init];
    NSString *str2 = [build builderPart];

    // 2.建立承包商
    Director *director = [[Director alloc] initWithBuilder:build];

    // 3.交付產品
    NSString *str = [director construct];
    NSLog(@"str = %@, str2 = %@",str, str2);

}

@end

使用構建者模式的需求:

客戶要店主一臺蘋果電腦, 電腦有CPU 顯示卡 主機板 系統
組裝者(指導者): 店主(Director)
構建者: 蘋果電腦
(協議) 生成者: CPU 顯示卡 主機板 系統

UML圖

Demo2
拓展生成者來處理最後的結構

首先建立協議類MacBuilder（生成者）

#import <Foundation/Foundation.h>
#import "MacComputerProtocol.h"

@protocol MacBuilder <NSObject>

// 構建CPU
- (id<MacBuilder>)buildCPU:(NSString *)cpu;

// 構建顯示卡
- (id<MacBuilder>)buildDisplay:(NSString *)display;

// 構建主機板
- (id<MacBuilder>)buildMainboard:(NSString *)mainboard;

// 構建系統
- (id<MacBuilder>)buildOS:(NSString *)os;

// 構建
- (id<MacComputerProtocol>)build;

@end

建立協議MacComputerProtocol

#import <Foundation/Foundation.h>

@protocol MacComputerProtocol <NSObject>

// 處理器
- (void)cpu:(NSString *)cpu;

// 顯示卡
- (void)display:(NSString *)display;

// 主機板
- (void)mainboard:(NSString *)mainboard;

// 系統
- (void)os;

@end

建立MacComputerBuilder類（構建者）

MacComputerBuilder.h

#import <Foundation/Foundation.h>
#import "MacBuilder.h"

@interface MacComputerBuilder : NSObject <MacBuilder>

@end

MacComputerBuilder.m

#import "MacComputerBuilder.h"
#import "MACComputer.h"

@interface MacComputerBuilder ()
@property (nonatomic, strong) id<MacComputerProtocol> computer;
@end

// 類似的呼叫方式, 就是典型的構建者呼叫模式
@implementation MacComputerBuilder

- (instancetype)init
{
    self = [super init];
    if (self) {
        _computer = [[MACComputer alloc] init];
    }
    return self;
}

// 構建CPU
- (id<MacBuilder>)buildCPU:(NSString *)cpu {
    [_computer cpu:cpu];
    return self;
}

// 構建顯示卡
- (id<MacBuilder>)buildDisplay:(NSString *)display {
    [_computer display:display];
    return self;
}

// 構建主機板
- (id<MacBuilder>)buildMainboard:(NSString *)mainboard {
    [_computer mainboard:mainboard];
    return self;
}

// 構建系統
- (id<MacBuilder>)buildOS:(NSString *)os {
    [_computer os];
    return self;
}

// 構建
- (id<MacComputerProtocol>)build {
    NSLog(@"構建了一臺蘋果電腦");
    //這種中間其實有很多邏輯需要處理，此次省略500行程式碼

    return _computer;
}
@end

建立MACComputer類
MACComputer.h

#import <Foundation/Foundation.h>
#import "MacComputerProtocol.h"

@interface MACComputer : NSObject <MacComputerProtocol>

@end

MACComputer.m

#import "MACComputer.h"

@implementation MACComputer
// 處理器
- (void)cpu:(NSString *)cpu {
    NSLog(@"Mac電腦處理器:%@",cpu);
}

// 顯示卡
- (void)display:(NSString *)display {
    NSLog(@"Mac電腦顯示卡:%@",display);
}

// 主機板
- (void)mainboard:(NSString *)mainboard {
    NSLog(@"Mac電腦主機板:%@",mainboard);

}

// 系統
- (void)os {
    NSLog(@"MAC系統");
}
@end

建立組裝者Director類

Director.h

#import <Foundation/Foundation.h>
#import "MacBuilder.h"

// 組裝
@interface Director : NSObject
- (instancetype)initWithBuilder:(id<MacBuilder>)builder;

// 成品的方法
- (void)constructCPU:(NSString *)cpu display:(NSString *)display mainboard:(NSString *)mainboard;

@end

Director.m

#import "Director.h"

@interface Director ()
@property (nonatomic, strong) id<MacBuilder> builder;
@end

@implementation Director
- (instancetype)initWithBuilder:(id<MacBuilder>)builder {
    self = [super init];
    if (self) {
        _builder = builder;
    }
    return self;
}

// 成品的方法
- (void)constructCPU:(NSString *)cpu display:(NSString *)display mainboard:(NSString *)mainboard {

    [[[[_builder buildCPU:cpu] buildDisplay:display] buildMainboard:mainboard] build];
}

@end

ViewController呼叫

#import "ViewController.h"
#import "Director.h"
#import "MacComputerBuilder.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    // 第一種構建方式
//    id<MacBuilder> build = [[MacComputerBuilder alloc] init];
//    // 構建者
//    Director *director = [[Director alloc] initWithBuilder:build];
//    [director constructCPU:@"Intel i8" display:@"獨立顯示卡" mainboard:@"超級主機板"];

    // 第二種方式
    id<MacBuilder> build = [[MacComputerBuilder alloc] init];
    // 構建者
    id<MacComputerProtocol> com = [[[[build buildCPU:@"Intel i8"] buildDisplay:@"du li xian ka"] buildMainboard:@"zhu ban"] build];
    NSLog(@"com = %@", com);

}

@end

實際開發中應用Demo

構建者模式變體

首先建立DrawBuilder類，再建立DrawView類
DrawView.h

#import <UIKit/UIKit.h>

@interface DrawView : UIView

@property (nonatomic, assign) CGFloat buildLabel;
@property (nonatomic, assign) CGFloat buildButton;
@property (nonatomic, assign) CGFloat buildSizeView;

@end

DrawView.m

#import "DrawView.h"

@implementation DrawView

- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame: frame];
    if (self) {
        self.backgroundColor = [UIColor grayColor];
    }
    return self;
}

// 使用drawRect,可以在控制器中設定值給view.
- (void)drawRect:(CGRect)rect {

    [self setBackgroundColor:[UIColor redColor]];
    // label
    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(self.buildLabel, 100, 50, 80)];
    label.text = @"TZ";
    label.textAlignment = NSTextAlignmentCenter;
    label.textColor = [UIColor blackColor];
    [self addSubview:label];

    // 按鈕
    UIButton *btn = [[UIButton alloc] initWithFrame:CGRectMake(100, self.buildButton, 100, 50)];
    [btn setTitle:@"藍色" forState:UIControlStateNormal];
    btn.titleLabel.backgroundColor = [UIColor redColor];
    btn.titleLabel.textAlignment = NSTextAlignmentCenter;
    [self addSubview:btn];

    // 新增view
    UIView *subView = [[UIView alloc] initWithFrame:CGRectMake(100, 200, 100, self.buildSizeView)];
    subView.backgroundColor = [UIColor blueColor];
    [self addSubview:subView];

    UIImage *backgroundImage = [UIImage imageNamed:@"tupian"];
    UIImageView *backgroundView = [[UIImageView alloc] initWithImage:backgroundImage];

    [self addSubview:backgroundView];
}

@end

DrawBuilder.h

#import <Foundation/Foundation.h>
#import "DrawView.h"

@interface DrawBuilder : NSObject

- (CGFloat)buildLabel;  /**< 構建label */
- (CGFloat)buildButton; /**< 構建按鈕 */
- (CGFloat)buildSizeView; /**< 構建藍色的View */

- (DrawView *)loadView; /**< 構建結果 */

@end

DrawBuilder.m

#import "DrawBuilder.h"

@implementation DrawBuilder
- (CGFloat)buildLabel {
    return 0;
}

- (CGFloat)buildButton {
    return 0;
}

- (CGFloat)buildSizeView {
    return 0;
}

- (DrawView *)loadView {
    CGFloat drawWidth = 200;
    CGFloat drawHeight = 300;

    DrawView *drawView = [[DrawView alloc] initWithFrame:CGRectMake(0, 0, drawWidth, drawHeight)];

    //
    drawView.buildLabel = [self buildLabel];
    drawView.buildButton = [self buildButton];
    drawView.buildSizeView = [self buildSizeView];

    return drawView;
}

@end

建立繼承自DrawBuilder類的DrawSubBuilderOne和DrawSubBuilderTeo

DrawSubBuilderOne.m

#import "DrawSubBuilderOne.h"

@implementation DrawSubBuilderOne
- (CGFloat)buildLabel {
    return 1;
}

- (CGFloat)buildButton {
    return 1;
}

- (CGFloat)buildSizeView {
    return 1;
}
@end

DrawSubBuilderTeo.m

#import "DrawSubBuilderTeo.h"

@implementation DrawSubBuilderTeo
- (CGFloat)buildLabel {
    return 10;
}

- (CGFloat)buildButton {
    return 150;
}

- (CGFloat)buildSizeView {
    return 100;
}
@end

建立Director組裝者
Director.h

#import <Foundation/Foundation.h>
#import "DrawBuilder.h"

@interface Director : NSObject

+ (DrawView *)creatView:(DrawBuilder *)builder;

@end

Director.m

#import "Director.h"

@implementation Director

+ (DrawView *)creatView:(DrawBuilder *)builder {
    DrawView *drawView = [builder loadView];
    return drawView;
}
@end

ViewController呼叫

#import "ViewController.h"
#import "DrawSubBuilderOne.h"
#import "DrawSubBuilderTeo.h"
#import "Director.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}
- (IBAction)btnClick:(id)sender {
    // 建立者
//    DrawBuilder *builder = [[DrawSubBuilderOne alloc] init];
    DrawBuilder *builder = [[DrawSubBuilderTeo alloc] init];

    // 組裝
    DrawView *drawView = [Director creatView:builder];

    drawView.center = self.view.center;
    [self.view addSubview:drawView];
}


@end