前言：

平时在使用一个对象的时候，尤其是在自定义控件中，如果它有很多属性，每个都要用“对象.属性”来设置的话，感觉有点繁琐，实际使用过程中，我们可以针对每个属性，设置单独的方法，方法返回相同的或者上一级的对象，在builder模式中也经常这样用

一、返回相同对象

1、例子

new BottomDialog(MainActivity.this)
    .title(R.string.title_item)             //设置标题
    .layout(BottomDialog.GRID)              //设置内容layout,默认为线性(LinearLayout)
    .orientation(BottomDialog.VERTICAL)     //设置滑动方向,默认为横向
    .inflateMenu(R.menu.menu_share)         //传人菜单内容
    .itemClick(new OnItemClickListener() {  //设置监听
        @Override
        public void click(Item item) {
            Toast.makeText(MainActivity.this, getString(R.string.share_title) + item.getTitle(), Toast.LENGTH_LONG).show();
        }
    })
    .show();

2、原理：全是BottomDialog，返回的都是BottomDialog对象

private CustomDialog customDialog;

    public BottomDialog(Context context) {
        customDialog = new CustomDialog(context);
    }

    public BottomDialog setGridItemNum(int num){
        GRID_ITEM_NUM=num;
        return this;
    }
    public BottomDialog title(String title) {
        customDialog.title(title);
        return this;
    }

    public BottomDialog title(int title) {
        customDialog.title(title);
        return this;
    }

    public BottomDialog background(int res) {
        customDialog.background(res);
        return this;
    }

    public BottomDialog inflateMenu(int menu) {
        customDialog.inflateMenu(menu);
        return this;
    }

    public BottomDialog layout(int layout) {
        customDialog.layout(layout);
        return this;
    }

    public BottomDialog orientation(int orientation) {
        customDialog.orientation(orientation);
        return this;
    }

    public BottomDialog addItems(List<Item> items) {
        customDialog.addItems(items);
        return this;
    }

    public BottomDialog itemClick(OnItemClickListener listener) {
        customDialog.setItemClick(listener);
        return this;
    }

    public void show() {
        customDialog.show();
    }

二、返回上一级对象

1、例子：可以参考Picasso源码中设置属性的方法

picasso
            .load(url) //Picasso内部的方法，返回RequestCreator对象
            .tag(tag)//RequestCreator内部的方法，返回RequestCreator对象
            .placeholder(R.drawable.bg_avatar_default)//RequestCreator内部的方法，返回RequestCreator对象
            .error(R.drawable.bg_avatar_default)//RequestCreator内部的方法，返回RequestCreator对象
            .transform(new CircleTransformation())//RequestCreator内部的方法，返回RequestCreator对象
            .into(iv);

2、原理：

tag()返回的是，load()返回的RequestCreator对象
而load()返回的是Picasso对象

   public RequestCreator load(String path) {
    if (path == null) {
      return new RequestCreator(this, null, 0);
    }
    if (path.trim().length() == 0) {
      throw new IllegalArgumentException("Path must not be empty.");
    }
    return load(Uri.parse(path));
  }
  
  
  public RequestCreator tag(Object tag) {
    if (tag == null) {
      throw new IllegalArgumentException("Tag invalid.");
    }
    if (this.tag != null) {
      throw new IllegalStateException("Tag already set.");
    }
    this.tag = tag;
    return this;
  }
  
  public RequestCreator placeholder(int placeholderResId) {
    if (!setPlaceholder) {
      throw new IllegalStateException("Already explicitly declared as no placeholder.");
    }
    if (placeholderResId == 0) {
      throw new IllegalArgumentException("Placeholder image resource invalid.");
    }
    if (placeholderDrawable != null) {
      throw new IllegalStateException("Placeholder image already set.");
    }
    this.placeholderResId = placeholderResId;
    return this;
  }
  
  public RequestCreator transform(Transformation transformation) {
    data.transform(transformation);
    return this;
  }
  
  ……