1.建造者模式的定义及使用场景
Builder模式是一步一步创建一个复制对象的创建型模式，他允许用户在不知道内部构建细节的情况下，可以更精细地控制对象的构造流程。改模式是为了将构造复杂对象的过程和它的部件解耦，使得构建过程和部件的表示隔离开来。
1.1定义
将一个复杂对象的构建与它的表示分离，使得同样的构建过程可以创建同步的表示
1.2使用场景
相同的方法，不同的执行顺序，产生不同的事件结果时多个部件或零件，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作用，这个时候使用建造者模式非常合适当初始化一个对象特别复杂，如参数多，而且很多参数都具有默认值时

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2.建造者模式的优缺点

2.1优点

封装性

建造者独立，容易扩展

便于控制细节风险

2.2缺点

会产生多余的Builder对象以及Director对象

3.建造者模式的实现方式

Product：

public class Product {  
    private  int id;  
    private  String  name;  
    public void doSomeThing(){  
        System.out.println("Product doSomeThing id:"+id+" name:"+name);  
    }  
  
  
    public void setId(int id) {  
        this.id = id;  
    }  
  
  
    public void setName(String name) {  
        this.name = name;  
    }  
  
  
    @Override  
    public String toString() {  
        return "Product{" +  
                "id=" + id +  
                ", name='" + name + '\'' +  
                '}';  
    }  
}```
AbstactBuilder:

public abstract class AbstactBulider {
abstract void setId(int id);
abstract void setName(String name);
abstract Product build();
}“`
Builder:

public class Builder extends AbstactBulider {  
    Product product = new Product();  
  
  
    @Override  
    void setId(int id) {  
        product.setId(id);  
    }  
  
  
    @Override  
    void setName(String name) {  
        product.setName(name);  
    }  
  
  
    @Override  
    Product build() {  
        return product;  
    }  
}```
Director:

public class Director {
private AbstactBulider aBuilder, bBuilder;

public Product getAProduct() {  
    aBuilder = new Builder();  
    aBuilder.setId(1);  
    aBuilder.setName("allen");  
    return aBuilder.build();  
}  


public Product getBProduct() {  
    bBuilder = new Builder();  
    bBuilder.setId(2);  
    bBuilder.setName("joy");  
    return bBuilder.build();  
}  

}“`
4.建造者模式在Android中的实际应用
在Android源码中，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。在开发过程中，我们经常用到AlertDialog，具体示例如下：

new AlertDialog.Builder(self)
  .setTitle("列表框")
  .setItems(new String[] {"列表项1","列表项2","列表项3"}, null)
  .setNegativeButton("确定", null)
  .show();```
从类名就可以看出这是一个Builder模式，通过Builder对象来组装Dialog的各个部分，如title、buttons、items等。分析AlertDialog源码如下：

public static class Builder {
private final AlertController.AlertParams P;
public Builder(Context context) {
this(context, resolveDialogTheme(context, 0));
}

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

public Context getContext() {
return P.mContext;
}

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

public Builder setTitle(CharSequence title) {
P.mTitle = title;
return this;
}

public Builder setCustomTitle(View customTitleView) {
P.mCustomTitleView = customTitleView;
return this;
}

public Builder setMessage(@StringRes int messageId) {
P.mMessage = P.mContext.getText(messageId);
return this;
}

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

public Builder setIcon(@DrawableRes int iconId) {
P.mIconId = iconId;
return this;
}

public Builder setIcon(Drawable icon) {
P.mIcon = icon;
return this;
}

public Builder setIconAttribute(@AttrRes int attrId) {
TypedValue out = new TypedValue();
P.mContext.getTheme().resolveAttribute(attrId, out, true);
P.mIconId = out.resourceId;
return this;
}

public Builder setPositiveButton(@StringRes int textId, final OnClickListener listener) {
P.mPositiveButtonText = P.mContext.getText(textId);
P.mPositiveButtonListener = listener;
return this;
}

public Builder setPositiveButton(CharSequence text, final OnClickListener listener) {
P.mPositiveButtonText = text;
P.mPositiveButtonListener = listener;
return this;
}

public Builder setNegativeButton(@StringRes int textId, final OnClickListener listener) {
P.mNegativeButtonText = P.mContext.getText(textId);
P.mNegativeButtonListener = listener;
return this;
}

public Builder setNegativeButton(CharSequence text, final OnClickListener listener) {
P.mNegativeButtonText = text;
P.mNegativeButtonListener = listener;
return this;
}

public Builder setNeutralButton(@StringRes int textId, final OnClickListener listener) {
P.mNeutralButtonText = P.mContext.getText(textId);
P.mNeutralButtonListener = listener;
return this;
}

public Builder setNeutralButton(CharSequence text, final OnClickListener listener) {
P.mNeutralButtonText = text;
P.mNeutralButtonListener = listener;
return this;
}
public Builder setCancelable(boolean cancelable) {
P.mCancelable = cancelable;
return this;
}

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

public Builder setOnKeyListener(OnKeyListener onKeyListener) {
P.mOnKeyListener = onKeyListener;
return this;
}

public Builder setItems(@ArrayRes int itemsId, final OnClickListener listener) {
P.mItems = P.mContext.getResources().getTextArray(itemsId);
P.mOnClickListener = listener;
return this;
}

public Builder setItems(CharSequence[] items, final OnClickListener listener) {
P.mItems = items;
P.mOnClickListener = listener;
return this;
}

public Builder setAdapter(final ListAdapter adapter, final OnClickListener listener) {
P.mAdapter = adapter;
P.mOnClickListener = listener;
return this;
}

public Builder setCursor(final Cursor cursor, final OnClickListener listener,
String labelColumn) {
P.mCursor = cursor;
P.mLabelColumn = labelColumn;
P.mOnClickListener = listener;
return this;
}

public Builder setMultiChoiceItems(@ArrayRes int itemsId, boolean[] checkedItems,
final OnMultiChoiceClickListener listener) {
P.mItems = P.mContext.getResources().getTextArray(itemsId);
P.mOnCheckboxClickListener = listener;
P.mCheckedItems = checkedItems;
P.mIsMultiChoice = true;
return this;
}

public Builder setMultiChoiceItems(CharSequence[] items, boolean[] checkedItems,
final OnMultiChoiceClickListener listener) {
P.mItems = items;
P.mOnCheckboxClickListener = listener;
P.mCheckedItems = checkedItems;
P.mIsMultiChoice = true;
return this;
}

public Builder setMultiChoiceItems(Cursor cursor, String isCheckedColumn, String labelColumn,
final OnMultiChoiceClickListener listener) {
P.mCursor = cursor;
P.mOnCheckboxClickListener = listener;
P.mIsCheckedColumn = isCheckedColumn;
P.mLabelColumn = labelColumn;
P.mIsMultiChoice = true;
return this;
}

public Builder setSingleChoiceItems(@ArrayRes int itemsId, int checkedItem,
final OnClickListener listener) {
P.mItems = P.mContext.getResources().getTextArray(itemsId);
P.mOnClickListener = listener;
P.mCheckedItem = checkedItem;
P.mIsSingleChoice = true;
return this;
}

public Builder setSingleChoiceItems(Cursor cursor, int checkedItem, String labelColumn,
final OnClickListener listener) {
P.mCursor = cursor;
P.mOnClickListener = listener;
P.mCheckedItem = checkedItem;
P.mLabelColumn = labelColumn;
P.mIsSingleChoice = true;
return this;
}

public Builder setSingleChoiceItems(CharSequence[] items, int checkedItem, final OnClickListener listener) {
P.mItems = items;
P.mOnClickListener = listener;
P.mCheckedItem = checkedItem;
P.mIsSingleChoice = true;
return this;
}

public Builder setSingleChoiceItems(ListAdapter adapter, int checkedItem, final OnClickListener listener) {
P.mAdapter = adapter;
P.mOnClickListener = listener;
P.mCheckedItem = checkedItem;
P.mIsSingleChoice = true;
return this;
}

public Builder setOnItemSelectedListener(final AdapterView.OnItemSelectedListener listener) {
P.mOnItemSelectedListener = listener;
return this;
}

public Builder setView(int layoutResId) {
P.mView = null;
P.mViewLayoutResId = layoutResId;
P.mViewSpacingSpecified = false;
return this;
}

public Builder setView(View view) {
P.mView = view;
P.mViewLayoutResId = 0;
P.mViewSpacingSpecified = false;
return this;
}

@Deprecated
public Builder setView(View view, int viewSpacingLeft, int viewSpacingTop,
int viewSpacingRight, int viewSpacingBottom) {
P.mView = view;
P.mViewLayoutResId = 0;
P.mViewSpacingSpecified = true;
P.mViewSpacingLeft = viewSpacingLeft;
P.mViewSpacingTop = viewSpacingTop;
P.mViewSpacingRight = viewSpacingRight;
P.mViewSpacingBottom = viewSpacingBottom;
return this;
}

@Deprecated
public Builder setInverseBackgroundForced(boolean useInverseBackground) {
P.mForceInverseBackground = useInverseBackground;
return this;
}

/**

• @hide
  */
  public Builder setRecycleOnMeasureEnabled(boolean enabled) {
  P.mRecycleOnMeasure = enabled;
  return this;
  }

public AlertDialog create() {
// Context has already been wrapped with the appropriate theme.
final AlertDialog dialog = new AlertDialog(P.mContext, 0, false);
P.apply(dialog.mAlert);
dialog.setCancelable(P.mCancelable);
if (P.mCancelable) {
dialog.setCanceledOnTouchOutside(true);
}
dialog.setOnCancelListener(P.mOnCancelListener);
dialog.setOnDismissListener(P.mOnDismissListener);
if (P.mOnKeyListener != null) {
dialog.setOnKeyListener(P.mOnKeyListener);
}
return dialog;
}

public AlertDialog show() {
final AlertDialog dialog = create();
dialog.show();
return dialog;
}
}“`
在AlertDialog的Builder模式中并没有看到Director角色出现，其实在很多场景中，Android并没有完全按照经典模式实现来做，而是做了一些修改，使得这个模式更易于使用。

这里的AlertDialog.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。当模块比较稳定，不存在一些变化时，可以在经典模式实现的基础上做一些精简，而不是生搬硬套，使程序失去架构之美。正是由于灵活地运用设计模式，Android的源码很值得我们深入学习。

出处：http://huangjunbin.com/page/3/