asp.net-mvc-4 - Mvc：创建方法以从类填充下拉列表并从控制器调用

Question

下面的代码在我的索引控制器操作中运行良好，该操作使用数据库数据填充下拉框。

我不想直接在我的控制器中使用它，因为我将在页面的多个位置使用下拉菜单。

var db = new StoreManagerEntities();
        var query = db.Categories.Select(c => new
        {
            CategoryId = c.CategoryID,
            Categoryname = c.CategoryName,
            IsSelected = c.CategoryID.Equals(0)
        });

        var model = new SelectViewModel
        {
            List = query.ToList()
                        .Select(c => new SelectListItem
                        {
                            Value = c.CategoryId.ToString(),
                            Text = c.Categoryname,
                            Selected = c.IsSelected,
                        })
        };

        return View(model);

我希望能够将代码放在一个方法中并从我的控制器调用此方法 这是另一个我希望该方法使用的类。

public class NorthwindDataContext
{

    StoreManagerEntities myDb = new StoreManagerEntities();

    //retrieve all category objects
    public List<Category> GetCategories()
    {
        return myDb.Categories.ToList();
    }

    //populate dropdownbox
        public void PopulateDropdown()
        {
              var query = db.Categories.Select(c => new
        {
            CategoryId = c.CategoryID,
            Categoryname = c.CategoryName,
            IsSelected = c.CategoryID.Equals(0)
        });

        var model = new SelectViewModel
        {
            List = query.ToList()
                        .Select(c => new SelectListItem
                        {
                            Value = c.CategoryId.ToString(),
                            Text = c.Categoryname,
                            Selected = c.IsSelected,
                        })
        };

        }


}

  Can you please show me how I can write the method here and have it 
  return the data I need back to the controller. It will be nice if you 
  can show me how to call this from the controller as well. 

Answer 1

你改变你的NorthwindDataContext班级怎么样

public class NorthwindDataContext
    {
        StoreManagerEntities myDb = new StoreManagerEntities();    
        //retrieve all category objects
        public List<Category> GetCategories()
        {
            return myDb.Categories.ToList();
        }    
        //populate dropdownbox
        public SelectViewModel PopulateDropdown()
        {
            var query = db.Categories.Select(c => new
                {
                    CategoryId = c.CategoryID,
                    Categoryname = c.CategoryName,
                    IsSelected = c.CategoryID.Equals(0)
                });

            var model = new SelectViewModel
            {
                List = query.ToList()
                            .Select(c => new SelectListItem
                            {
                                Value = c.CategoryId.ToString(),
                                Text = c.Categoryname,
                                Selected = c.IsSelected,
                            })
            };
            return model;

        }    

    }

PopulateDropdown()注意和的返回类型的变化return model;

并在控制器中使用它，例如：

var db = new NorthwindDataContext();
var model = db.PopulateDropdown();

return View(model);