1.建造者模式的定義及使用場(chǎng)景
Builder模式是一步一步創(chuàng)建一個(gè)復(fù)制對(duì)象的創(chuàng)建型模式吧享，他允許用戶在不知道內(nèi)部構(gòu)建細(xì)節(jié)的情況下芬为，可以更精細(xì)地控制對(duì)象的構(gòu)造流程。改模式是為了將構(gòu)造復(fù)雜對(duì)象的過程和它的部件解耦沐鼠，使得構(gòu)建過程和部件的表示隔離開來。
1.1定義
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)建過程可以創(chuàng)建同步的表示
1.2使用場(chǎng)景
相同的方法，不同的執(zhí)行順序习寸，產(chǎn)生不同的事件結(jié)果時(shí)多個(gè)部件或零件胶惰，都可以裝配到一個(gè)對(duì)象中傻工，但是產(chǎn)生的運(yùn)行結(jié)果又不相同時(shí)產(chǎn)品類非常復(fù)雜，或者產(chǎn)品類中的調(diào)用順序不同產(chǎn)生了不同的作用孵滞，這個(gè)時(shí)候使用建造者模式非常合適當(dāng)初始化一個(gè)對(duì)象特別復(fù)雜中捆，如參數(shù)多，而且很多參數(shù)都具有默認(rèn)值時(shí)

Paste_Image.png

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中的實(shí)際應(yīng)用
在Android源碼中泄伪，最常用到的Builder模式就是AlertDialog.Builder，使用該Builder來構(gòu)建復(fù)雜的AlertDialog對(duì)象匿级。在開發(fā)過程中蟋滴，我們經(jīng)常用到AlertDialog，具體示例如下：

new AlertDialog.Builder(self)
  .setTitle("列表框")
  .setItems(new String[] {"列表項(xiàng)1","列表項(xiàng)2","列表項(xiàng)3"}, null)
  .setNegativeButton("確定", null)
  .show();```
從類名就可以看出這是一個(gè)Builder模式痘绎，通過Builder對(duì)象來組裝Dialog的各個(gè)部分津函，如title、buttons孤页、items等尔苦。分析AlertDialog源碼如下：

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模式中并沒有看到Director角色出現(xiàn)，其實(shí)在很多場(chǎng)景中行施，Android并沒有完全按照經(jīng)典模式實(shí)現(xiàn)來做允坚，而是做了一些修改，使得這個(gè)模式更易于使用蛾号。

這里的AlertDialog.Builder同時(shí)扮演了上文中提到的builder稠项、ConcreteBuilder、Director的角色鲜结，簡(jiǎn)化了Builder模式的設(shè)計(jì)皿渗。當(dāng)模塊比較穩(wěn)定，不存在一些變化時(shí)轻腺，可以在經(jīng)典模式實(shí)現(xiàn)的基礎(chǔ)上做一些精簡(jiǎn)乐疆，而不是生搬硬套，使程序失去架構(gòu)之美贬养。正是由于靈活地運(yùn)用設(shè)計(jì)模式挤土，Android的源碼很值得我們深入學(xué)習(xí)。

出處：http://huangjunbin.com/page/3/