Android 架構(gòu)師之路 目錄

前言

建造者模式是設(shè)計(jì)模式的一種，將一個(gè)復(fù)雜對(duì)象的構(gòu)建與它的表示分離，使得同樣的構(gòu)建過(guò)程可以創(chuàng)建不同的表示。

1、建造者模式特征

1.1 建造者模式UML圖

Builder設(shè)計(jì)模式UML圖

1.2 建造者模式角色

在這樣的設(shè)計(jì)模式中，有以下幾個(gè)角色：

• builder：為創(chuàng)建一個(gè)產(chǎn)品對(duì)象的各個(gè)部件指定抽象接口。
• ConcreteBuilder：實(shí)現(xiàn)Builder的接口以構(gòu)造和裝配該產(chǎn)品的各個(gè)部件，定義并明確它所創(chuàng)建的表示，并 提供一個(gè)檢索產(chǎn)品的接口。
• Director：構(gòu)造一個(gè)使用Builder接口的對(duì)象。
• Product：表示被構(gòu)造的復(fù)雜對(duì)象。ConcreteBuilder創(chuàng)建該產(chǎn)品的內(nèi)部表示并定義它的裝配過(guò)程，包含定義組成部件的類，包括將這些部件裝配成最終產(chǎn)品的接口。

1.3 建造者模式使用場(chǎng)景

1. 創(chuàng)建復(fù)雜對(duì)象的算法獨(dú)立于組成對(duì)象的部件
2. 同一個(gè)創(chuàng)建過(guò)程需要有不同的內(nèi)部表象的產(chǎn)品對(duì)象

2、建造者模式代碼實(shí)現(xiàn)

2.1 標(biāo)準(zhǔn)寫法

builder:

/**
 * 抽象建造者
 * Created by Administrator on 2018/1/24.
 */
public interface Builder {
    public void makeWindow();

    public void makeFloor();

    public Room build();

}

ConcreteBuilder:

/**
 * Created by Administrator on 2018/1/24.
 * 持有對(duì)房子的引用
 */
public class WorkBuilder implements Builder {
    Room room = new Room();
    @Override
    public void makeWindow() {
        room.setWindow("歐式窗戶");
    }

    @Override
    public void makeFloor() {
        room.setFloor("日式地板");
    }

    @Override
    public Room build() {
        return room;
    }
}

Director:

/**
 * Created by Administrator on 2018/1/24.
 * 設(shè)計(jì)者(指導(dǎo)者)
 *
 * 他知道 房屋怎么設(shè)計(jì)
 * 他肯定對(duì) 工人所具備的能力有所理解
 */
public class Designer {
    public Room build(Builder builder){
        builder.makeFloor();
        builder.makeWindow();
        return builder.build();
    }
}

Product:

/**
 * Created by Administrator on 2018/1/24.
 */
public class Room {
    private String window;

    private String floor;

    public String getWindow() {
        return window;
    }

    public void setWindow(String window) {
        this.window = window;
    }

    public String getFloor() {
        return floor;
    }

    public void setFloor(String floor) {
        this.floor = floor;
    }

    @Override
    public String toString() {
        return "Room{" +
                "window='" + window + '\'' +
                ", floor='" + floor + '\'' +
                '}';
    }
}

Client調(diào)用:

public class Client {
    public static void main(String[] args) {
        Builder build = new WorkBuilder();
        Designer designer = new Designer();
        Room room = designer.build(build);
        System.out.println(room.toString());
        //房間暴露了構(gòu)建過(guò)程不合理
        room.setFloor("XXXXX");
        room.setWindow("XXXXX");
    }
}

運(yùn)行結(jié)果:

Room{window='歐式窗戶', floor='日式地板'}

注意：Product本身暴露了產(chǎn)品構(gòu)建過(guò)程不合理

2.2 變種優(yōu)化寫法

Product:

public class Room {
    private String window;

    private String floor;

    private String lamp;

    public Room apply(WorkBuilder.RoomParams params){
        window = params.window;
        floor = params.floor;
        lamp = params.floor;
        return this;
    }

    @Override
    public String toString() {
        return "Room{" +
                "window='" + window + '\'' +
                ", floor='" + floor + '\'' +
                ", lamp='" + lamp + '\'' +
                '}';
    }
}

ConcreteBuilder:

含有和Product同樣參數(shù)的內(nèi)部類RoomParams

public class WorkBuilder {
    Room room = new Room();
    private RoomParams params = new RoomParams();

    public WorkBuilder makeWindow(String window){
        params.window = window;
        return this;
    }
    public WorkBuilder makeFloor(String floor){
        params.floor = floor;
        return this;
    }
    public WorkBuilder makeLamp(String lamp){
        params.lamp = lamp;
        return this;
    }
    /**
     * 隱藏構(gòu)建過(guò)程
     *真正的構(gòu)建者
     *  */
    public Room build(){
        room.apply(params);
        return room;
    }

   public class RoomParams{
       public String window;

       public String floor;

       public String lamp;


    }
}

Client調(diào)用:

public class Client {
    public static void main(String[] args){
        //隱藏了構(gòu)建過(guò)程合理
        Room room = new WorkBuilder()
                .makeFloor("日式地板")
                .makeWindow("歐式窗戶")
                .makeLamp("中式吊燈")
                .build() ;

        System.out.println(room.toString());
    }
}

運(yùn)行結(jié)果:

Room{window='歐式窗戶', floor='日式地板', lamp='日式地板'}

Product類隱藏構(gòu)建過(guò)程，設(shè)計(jì)合理

3、Android源碼中使用

建造者典型例子是AlertDialog，它的基本寫法是:

public class AlertDialog extends Dialog implements DialogInterface {
    private AlertController mAlert;

    protected AlertDialog(Context context) {
        this(context, resolveDialogTheme(context, 0), true);
    }

    @Override
    public void setTitle(CharSequence title) {
        super.setTitle(title);
        mAlert.setTitle(title);
    }

    public void setMessage(CharSequence message) {
        mAlert.setMessage(message);
    }

    public static class Builder {
        private final AlertController.AlertParams P;
        private int mTheme;

        public Builder(Context context, int theme) {
            P = new AlertController.AlertParams(new ContextThemeWrapper(
                    context, resolveDialogTheme(context, theme)));
            mTheme = theme;
        }

        public Builder setTitle(int titleId) {
            P.mTitle = P.mContext.getText(titleId);
            return this;
        }

        public Builder setMessage(CharSequence message) {
            P.mMessage = message;
            return this;
        }

        public Builder setOnCancelListener(OnCancelListener onCancelListener) {
            P.mOnCancelListener = onCancelListener;
            return this;
        }

        public AlertDialog create() {
            final AlertDialog dialog = new AlertDialog(P.mContext, mTheme, false);
            P.apply(dialog.mAlert);
            dialog.setCancelable(P.mCancelable);
            if (P.mCancelable) {
                dialog.setCanceledOnTouchOutside(true);
            }
            dialog.setOnCancelListener(P.mOnCancelListener);
            ...
            return dialog;
        }

        public AlertDialog show() {
            AlertDialog dialog = create();
            dialog.show();
            return dialog;
        }
    }
}