Android 设计模式之Builder模式的简单使用

一、Builder模式介绍

Builder 模式是一步一步创建一个复杂对象的创建型模式，它允许用户在不知道内部构建细节的情况下。可以精细地控制对象的构造流程。Builder模式将复杂对象的构建过程和他的部件解耦，使得构建过程和部件的表示隔离开来。

二、使用场景

1. 相同的方法，但是有不同的执行顺序，产生了不同的结果

2. 多个零件和部件都可以装配到一个对象中，但是产生的运行结果不同

3. 初始化对象复杂，但是有很多默认的参数

三、结构图

1. Builder-抽象Builder类，规范产品的组建，一般是由子类实现具体的组建过程

2. ConcreteBuilder-具体的Builder类

3. Director-统一组装的过程

四、交互过程

client通过调用Director来创建不同的属性的对象，Director调用ConcreateBuilder创建所需属性的对象。层层封装，最终留给用户的只是一个调用的方法 Directo

五、简单的使用封装

下面是我使用Builder模式对Android AlertDialog的封装

在对象中调用，通过创建构造函数并调用showDialog()方法开启创建

 final MyOwnAlertDialog myOwnAlertDialog = new MyOwnAlertDialog(context, activity, title, null, "确定", "取消");
 myOwnAlertDialog.setOnDiaLogListener(new MyOwnAlertDialog.OnDialogListener() {            @Override
            public void dialogPositiveListener(View customView, DialogInterface dialogInterface, int which) {                //dosomthing
              }                  @Override
              public void error(String msg) {                //dosomthing
              }
              });
            }            @Override
            public void dialogNegativeListener(View customView, DialogInterface dialogInterface, int which) {

            }
          }).showDialog();
        }
      }
    });

构造器Builder，是构造一个使用Builder接口的对象:通过new CustomDialog.Builder 来创建对话框对象，并调用builder里的方法设置参数，创建一个一个的ConcreteBuilder产品

public class MyOwnAlertDialog {  private Activity activity;  private String dialogMessage;  private String dialogTitle;  private String positiveText;  private String negativeText;  private View dialogView;  private int customeLayoutId;  private Context context;  private OnDialogListener listener;  private CustomDialog.Builder dialog;  //带有自定义view的构造器
  public MyOwnAlertDialog(Context context, Activity activity, int customeLayoutId, String dialogTitle, String positiveText, String negativeText) {    this.context = context;    this.activity = activity;    this.customeLayoutId = customeLayoutId;    this.dialogTitle = dialogTitle;    this.positiveText = positiveText;    this.negativeText = negativeText;    this.dialogView = View.inflate(context, customeLayoutId, null);
  }  //不带自定义view的构造器,
  public MyOwnAlertDialog(Context context, Activity activity, String dialogMessage, String dialogTitle, String positiveText, String negativeText) {    this.context = context;    this.activity = activity;    this.dialogTitle = dialogTitle;    this.dialogMessage = dialogMessage;    this.positiveText = positiveText;    this.negativeText = negativeText;
  }  public void showDialog() {
    dialog = new CustomDialog.Builder(context, activity);
    dialog.setTitle(dialogTitle);//设置标题
    //注意:dialogMessage和dialogView是互斥关系也就是dialogMessage存在dialogView就不存在,dialogView不存在dialogMessage就存在
    if (dialogMessage != null) {
      dialog.setMessage(dialogMessage);//设置对话框内容
    } else {
      dialog.setContentView(dialogView);//设置对话框的自定义view对象
    }    /**
     * 尽管有两个点击事件监听器,可以通过我们自定义的监听器设置一个标记变量,从而可以实现将两个点击事件合并成一个
     * 监听器OnDialogListener
     * */
    //确定意图传入positive标记值
    dialog.setPositiveButton(positiveText, new DialogInterface.OnClickListener() {      @Override
      public void onClick(DialogInterface dialogInterface, int which) {
        dialogInterface.dismiss();        if (listener != null) {
          listener.dialogPositiveListener(dialogView, dialogInterface, which);
        }
      }      //取消意图传入negative标记值
    }).setNegativeButton(negativeText, new DialogInterface.OnClickListener() {      @Override
      public void onClick(DialogInterface dialogInterface, int which) {
        dialogInterface.dismiss();        if (listener != null) {
          listener.dialogNegativeListener(dialogView, dialogInterface, which);
        }
      }
    }).create().show();
  }  //注册监听器方法
  public MyOwnAlertDialog setOnDiaLogListener(OnDialogListener listener) {    this.listener = listener;    return this;//把当前对象返回,用于链式编程
  }  //定义一个监听器接口
  public interface OnDialogListener {    //customView　这个参数需要注意就是如果没有自定义view,那么它则为null
    public void dialogPositiveListener(View customView, DialogInterface dialogInterface, int which);    public void dialogNegativeListener(View customView, DialogInterface dialogInterface, int which);
  }

}

ConcreteBuilder构建，基础的ConcreteBuilder，定义个体的方法

/**
 * 建造者模式封装自定义dialog
 * Created by david on 2016/12/21.
 */public class CustomDialog extends Dialog {  private static CustomDialog dialog;  public CustomDialog(Context context) {    super(context);
  }  public CustomDialog(Context context, int themeResId) {    super(context, themeResId);
  }  public static class Builder{    private Activity activity;    private Context context;    private String message;    private String title;    private View contentView;    private String positiveButtonText;    private String negativeButtonText;    private OnClickListener positiveButtonClickListener;    private OnClickListener negativeButtonClickListener;    public Builder(Context context, Activity activity) {      this.context = context;      this.activity = activity;
    }    public Builder setMessage(String message) {      this.message = message;      return this;
    }    public Builder setMessage(int message) {      this.message = (String) context.getText(message);      return this;
    }    public Builder setTitle(int title) {      this.title = (String) context.getText(title);      return this;
    }    public Builder setTitle(String title) {      this.title = title;      return this;
    }    public Builder setContentView(View v) {      this.contentView = v;      return this;
    }    public Builder setPositiveButton(int positiveButtonText,
                     OnClickListener listener) {      this.positiveButtonText = (String) context
          .getText(positiveButtonText);      this.positiveButtonClickListener = listener;      return this;
    }    public Builder setPositiveButton(String positiveButtonText,
                     OnClickListener listener) {      this.positiveButtonText = positiveButtonText;      this.positiveButtonClickListener = listener;      return this;
    }    public Builder setNegativeButton(int negativeButtonText,
                     OnClickListener listener) {      this.negativeButtonText = (String) context
          .getText(negativeButtonText);      this.negativeButtonClickListener = listener;      return this;
    }    public Builder setNegativeButton(String negativeButtonText,
                     OnClickListener listener) {      this.negativeButtonText = negativeButtonText;      this.negativeButtonClickListener = listener;      return this;
    }    public CustomDialog create() {
      LayoutInflater inflater = (LayoutInflater) context
          .getSystemService(Context.LAYOUT_INFLATER_SERVICE);      // instantiate the dialog with the custom Theme
      dialog = new CustomDialog(context,R.style.Dialog);
      View layout = inflater.inflate(R.layout.myownalertdialog_layout, null);
      dialog.addContentView(layout, new ViewGroup.LayoutParams(
          ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));
      DisplayMetrics dm = new DisplayMetrics();      //设置窗体大小
      activity.getWindowManager().getDefaultDisplay().getMetrics(dm);      int screenWidth = dm.widthPixels;      int screenHeigh = dm.heightPixels;      int heigh = screenHeigh * 7 / 30;      int weight = screenWidth * 6 / 8;
      android.view.Window window = dialog.getWindow();
      window.setLayout(weight, heigh);
      window.setBackgroundDrawableResource(R.drawable.dialog_shape);      // set the dialog title
      //((TextView) layout.findViewById(R.id.title)).setText(title);
      // set the confirm button
      if (positiveButtonText != null) {
        ((TextView) layout.findViewById(R.id.sure))
            .setText(positiveButtonText);        if (positiveButtonClickListener != null) {
          ((TextView) layout.findViewById(R.id.sure))
              .setOnClickListener(new View.OnClickListener() {                public void onClick(View v) {
                  positiveButtonClickListener.onClick(dialog,
                      DialogInterface.BUTTON_POSITIVE);
                }
              });
        }
      } else {        // if no confirm button just set the visibility to GONE
        /* layout.findViewById(R.id.back).setVisibility(
            View.GONE);*/
      }      // set the cancel button
      if (negativeButtonText != null) {
        ((TextView) layout.findViewById(R.id.cancle))
            .setText(negativeButtonText);        if (negativeButtonClickListener != null) {
          ((TextView) layout.findViewById(R.id.cancle))
              .setOnClickListener(new View.OnClickListener() {                public void onClick(View v) {
                  negativeButtonClickListener.onClick(dialog,
                      DialogInterface.BUTTON_NEGATIVE);
                }
              });
        }
      } else {        // if no confirm button just set the visibility to GONE
        /* layout.findViewById(R.id.cancle).setVisibility(
            View.GONE);*/
      }      // set the content message
      if (message != null) {
        ((TextView) layout.findViewById(R.id.alert2_title)).setText(message);
      } else if (contentView != null) {        // if no message set
        // add the contentView to the dialog body
        ((LinearLayout) layout.findViewById(R.id.content))
            .removeAllViews();
        ((LinearLayout) layout.findViewById(R.id.content)).addView(
            contentView, new ActionBar.LayoutParams(
                ViewGroup.LayoutParams.FILL_PARENT,
                ViewGroup.LayoutParams.FILL_PARENT));
      }
      dialog.setContentView(layout);      return dialog;
    }

  }

}

上述示例中，通过具体的CustomDialog来封装具体的内容，通过MyOwnAlertDialog来构建具体的对象，他们一起将一个复杂对象的构建和他的表示分离，使得同样的构建过程可以创建不同的对象

六、总结

Builder模式在各类开发中都比较常见，通常作为配置类的构建器将配置的构建和表示分离开来，同时也是将配置从目标类分离出来，避免过多的方法, 有良好的封装性，使得代码易修改，独立，容易扩展

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