设计模式-建造者模式

最新推荐文章于 2025-09-23 11:32:09 发布

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#Android #设计模式 #Builder #建造者模式 #AlertDialog

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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

2.建造者模式的优缺点

2.1优点

1）封装性
2）建造者独立，容易扩展
2）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。