Builder设计模式

1. 概述

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　　上一期的热修复相对来说有点难度，我其实也没往深里说如果实在看不懂可以看看视频，其实最主要的还是思路代码也就那么几行，这一期我们又回归到设计模式，相对来说要简单不少，这一期要讲的是一行代码如何显示所有弹出框效果。

　　视频地址：http://pan.baidu.com/s/1gfwZfF1

　　相关文章：

　　2017Android进阶之路与你同行

　　Builder设计模式 - 构建整个项目的万能Dialog

　　Builder设计模式 - 构建整个应用的NavigationBar
　　
　　

2. 模式介绍

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模式的定义

将一个复杂对象的构建与它的表示分离，使得不同的构建过程可以创建不同的显示，但其根本还是不变。

模式的使用场景

1. 相同的方法，不同的执行顺序，产生不同的事件结果时；
2. 多个部件或零件，都可以装配到一个对象中，但是产生的运行结果又不相同时；
3. 产品类非常复杂，或者产品类中的调用顺序不同产生了不同的效能，这个时候使用建造者模式非常合适。

3. UML类图

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角色介绍
- Product 产品类 : 产品的抽象类；
- Builder : 抽象类， 规范产品的组建，一般是由子类实现具体的组件过程；
- ConcreteBuilder : 具体的构建器；
- Director : 统一组装过程(可省略)。

4. 模式的简单实现

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简单实现的介绍

电脑的组装过程较为复杂，步骤繁多，但是顺序却是不固定的。下面我们以组装电脑为例来演示一下简单且经典的builder模式。

实现源码

package com.dp.example.builder;/** * Computer产品抽象类, 为了例子简单, 只列出这几个属性 *  * @author mrsimple * */public abstract class Computer {    protected int mCpuCore = 1;    protected int mRamSize = 0;    protected String mOs = "Dos";    protected Computer() {    }    // 设置CPU核心数    public abstract void setCPU(int core);    // 设置内存    public abstract void setRAM(int gb);    // 设置操作系统    public abstract void setOs(String os);    @Override    public String toString() {        return "Computer [mCpuCore=" + mCpuCore + ", mRamSize=" + mRamSize                + ", mOs=" + mOs + "]";    }}package com.dp.example.builder;/** * Apple电脑 */public class AppleComputer extends Computer {    protected AppleComputer() {    }    @Override    public void setCPU(int core) {        mCpuCore = core;    }    @Override    public void setRAM(int gb) {        mRamSize = gb;    }    @Override    public void setOs(String os) {        mOs = os;    }}package com.dp.example.builder;package com.dp.example.builder;/** * builder抽象类 * */public abstract class Builder {    // 设置CPU核心数    public abstract void buildCPU(int core);    // 设置内存    public abstract void buildRAM(int gb);    // 设置操作系统    public abstract void buildOs(String os);    // 创建Computer    public abstract Computer create();}package com.dp.example.builder;public class ApplePCBuilder extends Builder {    private Computer mApplePc = new AppleComputer();    @Override    public void buildCPU(int core) {        mApplePc.setCPU(core);    }    @Override    public void buildRAM(int gb) {        mApplePc.setRAM(gb);    }    @Override    public void buildOs(String os) {        mApplePc.setOs(os);    }    @Override    public Computer create() {        return mApplePc;    }}package com.dp.example.builder;public class Director {    Builder mBuilder = null;    /**     *      * @param builder     */    public Director(Builder builder) {        mBuilder = builder;    }    /**     * 构建对象     *      * @param cpu     * @param ram     * @param os     */    public void construct(int cpu, int ram, String os) {        mBuilder.buildCPU(cpu);        mBuilder.buildRAM(ram);        mBuilder.buildOs(os);    }}/** * 经典实现较为繁琐 *  * @author mrsimple * */public class Test {    public static void main(String[] args) {        // 构建器        Builder builder = new ApplePCBuilder();        // Director        Director pcDirector = new Director(builder);        // 封装构建过程, 4核, 内存2GB, Mac系统        pcDirector.construct(4, 2, "Mac OS X 10.9.1");        // 构建电脑, 输出相关信息        System.out.println("Computer Info : " + builder.create().toString());    }}

通过Builder来构建产品对象, 而Director封装了构建复杂产品对象对象的过程，不对外隐藏构建细节。

5. Android源码中的模式实现

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在Android源码中，我们最常用到的Builder模式就是AlertDialog.Builder， 使用该Builder来构建复杂的AlertDialog对象。简单示例如下 :

    //显示基本的AlertDialog      private void showDialog(Context context) {          AlertDialog.Builder builder = new AlertDialog.Builder(context);          builder.setIcon(R.drawable.icon);          builder.setTitle("头部");          builder.setMessage("内容");          builder.setPositiveButton("Button1",                  new DialogInterface.OnClickListener() {                      public void onClick(DialogInterface dialog, int whichButton) {                          setTitle("点击了对话框上的Button1");                      }                  })　　　　　　　　.setNeutralButton("Button2",                  new DialogInterface.OnClickListener() {                      public void onClick(DialogInterface dialog, int whichButton) {                          setTitle("点击了对话框上的Button2");                      }                  });          builder.create().show();  // 构建AlertDialog， 并且显示    } 

效果就不演示了没什么好看的，如果是v7包中的AlertDialog还看得下去，如果是v4包中的惨目忍睹。下面我们看看AlertDialog的相关源码，你看的可能和我的不一样但大致差不多你懂的：

// AlertDialogpublic class AlertDialog extends Dialog implements DialogInterface {    // Controller, 接受Builder成员变量P中的各个参数    private AlertController mAlert;    // 构造函数    protected AlertDialog(Context context, int theme) {        this(context, theme, true);    }    // 4 : 构造AlertDialog    AlertDialog(Context context, int theme, boolean createContextWrapper) {        super(context, resolveDialogTheme(context, theme), createContextWrapper);        mWindow.alwaysReadCloseOnTouchAttr();        mAlert = new AlertController(getContext(), this, getWindow());    }    // 实际上调用的是mAlert的setTitle方法    @Override    public void setTitle(CharSequence title) {        super.setTitle(title);        mAlert.setTitle(title);    }    // 实际上调用的是mAlert的setCustomTitle方法    public void setCustomTitle(View customTitleView) {        mAlert.setCustomTitle(customTitleView);    }    public void setMessage(CharSequence message) {        mAlert.setMessage(message);    }    // AlertDialog其他的代码省略    // ************  Builder为AlertDialog的内部类   *******************    public static class Builder {        // 1 : 存储AlertDialog的各个参数, 例如title, message, icon等.        private final AlertController.AlertParams P;        // 属性省略        /**         * Constructor using a context for this builder and the {@link AlertDialog} it creates.         */        public Builder(Context context) {            this(context, resolveDialogTheme(context, 0));        }        public Builder(Context context, int theme) {            P = new AlertController.AlertParams(new ContextThemeWrapper(                    context, resolveDialogTheme(context, theme)));            mTheme = theme;        }        // Builder的其他代码省略 ......        // 2 : 设置各种参数        public Builder setTitle(CharSequence title) {            P.mTitle = title;            return this;        }        public Builder setMessage(CharSequence message) {            P.mMessage = message;            return this;        }        public Builder setIcon(int iconId) {            P.mIconId = iconId;            return this;        }        public Builder setPositiveButton(CharSequence text, final OnClickListener listener) {            P.mPositiveButtonText = text;            P.mPositiveButtonListener = listener;            return this;        }        public Builder setView(View view) {            P.mView = view;            P.mViewSpacingSpecified = false;            return this;        }        // 3 : 构建AlertDialog, 传递参数        public AlertDialog create() {            // 调用new AlertDialog构造对象， 并且将参数传递个体AlertDialog             final AlertDialog dialog = new AlertDialog(P.mContext, mTheme, false);            // 5 : 将P中的参数应用的dialog中的mAlert对象中            P.apply(dialog.mAlert);            dialog.setCancelable(P.mCancelable);            if (P.mCancelable) {                dialog.setCanceledOnTouchOutside(true);            }            dialog.setOnCancelListener(P.mOnCancelListener);            if (P.mOnKeyListener != null) {                dialog.setOnKeyListener(P.mOnKeyListener);            }            return dialog;        }    }}

可以看到，通过Builder来设置AlertDialog中的title, message, button等参数， 这些参数都存储在类型为AlertController.AlertParams的成员变量P中，AlertController.AlertParams中包含了与之对应的成员变量。在调用Builder类的create函数时才创建AlertDialog, 并且将Builder成员变量P中保存的参数应用到AlertDialog的mAlert对象中，即P.apply(dialog.mAlert)代码段。我们看看apply函数的实现 :

   public void apply(AlertController dialog) {        if (mCustomTitleView != null) {            dialog.setCustomTitle(mCustomTitleView);        } else {            if (mTitle != null) {                dialog.setTitle(mTitle);            }            if (mIcon != null) {                dialog.setIcon(mIcon);            }            if (mIconId >= 0) {                dialog.setIcon(mIconId);            }            if (mIconAttrId > 0) {                dialog.setIcon(dialog.getIconAttributeResId(mIconAttrId));            }        }        if (mMessage != null) {            dialog.setMessage(mMessage);        }        if (mPositiveButtonText != null) {            dialog.setButton(DialogInterface.BUTTON_POSITIVE, mPositiveButtonText,                    mPositiveButtonListener, null);        }        if (mNegativeButtonText != null) {            dialog.setButton(DialogInterface.BUTTON_NEGATIVE, mNegativeButtonText,                    mNegativeButtonListener, null);        }        if (mNeutralButtonText != null) {            dialog.setButton(DialogInterface.BUTTON_NEUTRAL, mNeutralButtonText,                    mNeutralButtonListener, null);        }        if (mForceInverseBackground) {            dialog.setInverseBackgroundForced(true);        }        // For a list, the client can either supply an array of items or an        // adapter or a cursor        if ((mItems != null) || (mCursor != null) || (mAdapter != null)) {            createListView(dialog);        }        if (mView != null) {            if (mViewSpacingSpecified) {                dialog.setView(mView, mViewSpacingLeft, mViewSpacingTop, mViewSpacingRight,                        mViewSpacingBottom);            } else {                dialog.setView(mView);            }        }    }

实际上就是把P中的参数挨个的设置到AlertController中， 也就是AlertDialog中的mAlert对象。从AlertDialog的各个setter方法中我们也可以看到，实际上也都是调用了mAlert对应的setter方法。在这里，Builder同时扮演了上文中提到的builder、ConcreteBuilder、Director的角色，简化了Builder模式的设计。

6. 构建整个应用的万能Dialog

　　
　　AlertDialog其实在我们的开发过程中可能没卵用，一般设计师设计出来的基本都是仿照的IOS的效果，这样一来就算再好用也与我们无缘。而且在我们的开发过程中效果千奇百怪时而这样，时而那样头疼得很啊，接下来我们就打算采用系统已经提供好的Builder设计模式构建整个应用的万能Dialog，代码可以参考系统的AlertDialog，最终无论什么复杂的效果一行能搞定算得上勉勉强强。

public static class Builder {        private AlertController.AlertParams P;        public Builder(Context context) {            this(context, 0);        }        public Builder(Context context, int themeResId) {            P = new AlertController.AlertParams();            P.themeResId = themeResId;            P.context = context;        }        public Builder setText(int viewId, CharSequence text) {            P.textArray.put(viewId, text);            return this;        }        public Builder setOnClickListener(int viewId, View.OnClickListener listener) {            P.clickArray.put(viewId, listener);            return this;        }        public Builder setContentView(int layoutId) {            P.view = null;            P.layoutId = layoutId;            return this;        }        public Builder setContentView(View view) {            P.layoutId = 0;            P.view = view;            return this;        }        /**         * Sets whether the dialog is cancelable or not.  Default is true.         *         * @return This Builder object to allow for chaining of calls to set methods         */        public Builder setCancelable(boolean cancelable) {            P.cancelable = cancelable;            return this;        }        /**         * Sets the callback that will be called if the dialog is canceled.         * <p>         * <p>Even in a cancelable dialog, the dialog may be dismissed for reasons other than         * being canceled or one of the supplied choices being selected.         * If you are interested in listening for all cases where the dialog is dismissed         * and not just when it is canceled, see         * {@link #setOnDismissListener(OnDismissListener) setOnDismissListener}.</p>         *         * @return This Builder object to allow for chaining of calls to set methods         * @see #setCancelable(boolean)         * @see #setOnDismissListener(OnDismissListener)         */        public Builder setOnCancelListener(OnCancelListener onCancelListener) {            P.onCancelListener = onCancelListener;            return this;        }        /**         * Sets the callback that will be called when the dialog is dismissed for any reason.         *         * @return This Builder object to allow for chaining of calls to set methods         */        public Builder setOnDismissListener(OnDismissListener onDismissListener) {            P.onDismissListener = onDismissListener;            return this;        }        /**         * Sets the callback that will be called if a key is dispatched to the dialog.         *         * @return This Builder object to allow for chaining of calls to set methods         */        public Builder setOnKeyListener(OnKeyListener onKeyListener) {            P.onKeyListener = onKeyListener;            return this;        }        /**         * Creates an {@link AlertDialog} with the arguments supplied to this         * builder.         * <p/>         * Calling this method does not display the dialog. If no additional         * processing is needed, {@link #show()} may be called instead to both         * create and display the dialog.         */        public BaseDialog create() {            // Context has already been wrapped with the appropriate theme.            final BaseDialog dialog = new BaseDialog(P.context, P.themeResId);            P.apply(dialog.mAlert);            dialog.setCancelable(P.cancelable);            if (P.cancelable) {                dialog.setCanceledOnTouchOutside(true);            }            dialog.setOnCancelListener(P.onCancelListener);            dialog.setOnDismissListener(P.onDismissListener);            if (P.onKeyListener != null) {                dialog.setOnKeyListener(P.onKeyListener);            }            return dialog;        }        /**         * Creates an {@link AlertDialog} with the arguments supplied to this         * builder and immediately displays the dialog.         * <p/>         * Calling this method is functionally identical to:         * <pre>         *     AlertDialog dialog = builder.create();         *     dialog.show();         * </pre>         */        public BaseDialog show() {            final BaseDialog dialog = create();            dialog.show();            return dialog;        }    }

class AlertController {    private DialogViewHelper mViewHelper;    private BaseDialog mDialog;    private Window mWindow;    public AlertController(BaseDialog dialog, Window window) {        mDialog = dialog;        mWindow = window;    }    /**     * 获取Dialog     * @return     */    public BaseDialog getDialog() {        return mDialog;    }    /**     * 获取window     * @return     */    public Window getWindow() {        return mWindow;    }    public DialogViewHelper getViewHelper() {        return mViewHelper;    }    /**     * 设置View的辅助     * @param viewHelper     */    public void setDialogViewHelper(DialogViewHelper viewHelper) {        this.mViewHelper = viewHelper;    }    /**     * 设置文本     * @param viewId     * @param text     */    public void setText(int viewId, CharSequence text) {        mViewHelper.setText(viewId, text);    }    /**     * 设置点击事件     * @param viewId     * @param listener     */    public void setOnClickListener(int viewId, View.OnClickListener listener) {        mViewHelper.setOnClickListener(viewId, listener);    }    /**     * 通过id获取View     * @param viewId     * @param <T>     * @return     */    public <T extends View> T getView(int viewId) {        return mViewHelper.getView(viewId);    }}

以后我们显示任何的弹出框效果都只需要一行了：

    @Override    public void onClick(View v) {        BaseDialog dialog = new BaseDialog.Builder(this)                .setContentView(R.layout.detail_comment_dialog).fullWith()                .fromBottom(false)                .show();    }

不过这明明有四行，接下来我们来说一下好处，Builder设计模式的好处就不说了网上太多了，我们就只说在真正的开发中这么做的好处：
1. 良好的封装性， 使用建造者模式你不必知道内部的细节，只要知道我想要什么效果就行了；
2. 建造者独立，容易扩展，不过我们不需要扩展了，这么多年碰到的效果都在里面了；
3. 在对象创建过程中会使用到系统中的一些其它对象，这些对象在创建过程中不易得到；
4. 大大节省了代码量，按照我们之前的那种写法没个几行写不出这效果，这里就一行而且效果完全自定义。

视频地址：http://pan.baidu.com/s/1gfwZfF1

相关文章：

　　2017Android进阶之路与你同行

　　Android Builder设计模式 - 构建整个项目的万能Dialog

　　Builder设计模式 - 构建整个应用的NavigationBar