我一直在研究 Commonsware Android 编程教程,在教程 5 中,额外的学分 2,挑战是使用多个布局来显示 ListView 中的行,具体取决于对象的“类型名称”(a Restaurant 的“type”属性,它是一个 String)。因此,它建议在自定义 ArrayAdapter 中重写getItemViewType和getViewTypeCount。此外,

在这种情况下，遵循此配方并重写这两种方法工作正常，但基于检查该 Restaurant“type”属性的值导致冗余逻辑。例如（请注意，此适配器是内部类，restaurants是声明为外部 Activity 成员的 Restaurant 对象的 ArrayList）：

class RestaurantsAdapter extends ArrayAdapter<Restaurant> {
  private static final int ROW_TYPE_DELIVERY = 0;
  private static final int ROW_TYPE_TAKE_OUT = 1;
  private static final int ROW_TYPE_SIT_DOWN = 2;
  RestaurantsAdapter() {
    super(LunchListActivity.this, android.R.layout.simple_list_item_1, restaurants);
  }
  public int getViewTypeCount() {
    return 3;
  }
  public int getItemViewType(int position) {
    String type = restaurants.get(position).getType();
    if (type == "delivery") {
      return ROW_TYPE_DELIVERY;
    } else if (type == "take_out") {
      return ROW_TYPE_TAKE_OUT;
    } else {
      return ROW_TYPE_SIT_DOWN;
    }
  }
  // Sets the icon, name and address of the Restaurant for the view.
  public View getView(int position, View convertView, ViewGroup parent) {
    View row = convertView;
    RestaurantHolder viewHolder;
    if (row == null) {
      LayoutInflater inflater = getLayoutInflater();
      switch (getItemViewType(position)) {
        case ROW_TYPE_DELIVERY:
          row = inflater.inflate(R.layout.row_delivery, null);
          break;
        case ROW_TYPE_TAKE_OUT:
          row = inflater.inflate(R.layout.row_take_out, null);
          break;
        default:
          row = inflater.inflate(R.layout.row_sit_down, null);
          break;
      }
      viewHolder = new RestaurantHolder(row);
      row.setTag(viewHolder);
    } else {
      viewHolder = (RestaurantHolder)row.getTag();
    }
    viewHolder.populateFrom(restaurants.get(position));
    return row;
  }
}

我的错误是重复的逻辑（getItemViewType中的 if / else 和switchgetView）。

class RestaurantsAdapter extends ArrayAdapter<Restaurant> {
  RestaurantsAdapter() {
    super(LunchListActivity.this, android.R.layout.simple_list_item_1, restaurants);
  }
  // Sets the icon, name and address of the Restaurant for the view.
  public View getView(int position, View convertView, ViewGroup parent) {
    View row = convertView;
    RestaurantHolder viewHolder;
    if (row == null) {
      LayoutInflater inflater = getLayoutInflater();
      if (restaurants.get(position).getType() == "delivery") {
        row = inflater.inflate(R.layout.row_delivery, null);
      } else if (restaurants.get(position).getType() == "take_out") {
        row = inflater.inflate(R.layout.row_take_out, null);
      } else {
        row = inflater.inflate(R.layout.row_sit_down, null);
      }
      viewHolder = new RestaurantHolder(row);
      row.setTag(viewHolder);
    } else {
      viewHolder = (RestaurantHolder)row.getTag();
    }
    viewHolder.populateFrom(restaurants.get(position));
    return row;
  }
}

这实现了动态加载三个 xml 布局之一的目标，消除了冗余逻辑，稍微减少了代码与布局数量的耦合，并且不需要覆盖getViewTypeCount和getItemViewType。

我的问题是：为什么要覆盖这两种方法，如果一个没有？