asp.net mvc 2 简简单单做开发 自定义DropdownList控件

　　asp.net mvc 2 给我们提供了强大的自定义功能，今天主要说下DropdownList自定义绑定字段显示，通过ViewData设定DropdownList的数据项。自动绑定显示。实现的方式。在global.asax 中注册 FieldTemplateMetadataProvider，

 ModelMetadataProviders.Current = new mvc.Models.FieldTemplateMetadataProvider();
通过返回的 FieldTemplateMetadata 。在MetaData中指定使用DropDownList的字段
       [Display( Name="",Order=12)]
        [Required]
        [SearchFilter]
        [DisplayName("栏目")]
        [DropDownList("Category", "Id", "Name")]
        public int Cid { get; set; }

通过DropDownList指定调用的模板为dropdownlist.ascx ,在dropdownlist.ascx 将默认的 ModelMetadata 转成FieldTemplateMetadata 获取 DropDownListAttribute 。

<script runat="server">
    DropDownListAttribute GetDropDownListAttribute()
    {
        FieldTemplateMetadata metaData = ViewData.ModelMetadata as FieldTemplateMetadata;
 
        return (metaData != null) ? metaData.Attributes.OfType<DropDownListAttribute>().SingleOrDefault() : null;
    }
</script>

 
　　通过DropDownListAttribute 获得 ViewData的key ，绑定的文本对应的字段，值对应的字段，使用html.DropDownlist显示数据

    DropdownList.ascx 代码

<%@ Import Namespace="mvc.Models"%>
<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl" %>
<script runat="server">
    DropDownListAttribute GetDropDownListAttribute()
    {
        FieldTemplateMetadata metaData = ViewData.ModelMetadata as FieldTemplateMetadata;

        return (metaData != null) ? metaData.Attributes.OfType<DropDownListAttribute>().SingleOrDefault() : null;
    }
</script>
<% DropDownListAttribute attribute = GetDropDownListAttribute();%>
<% if (attribute != null) {%>
    <%= Html.DropDownList(string.Empty, new SelectList(ViewData[attribute.ViewDataKey] as IEnumerable, attribute.DataValueField, attribute.DataTextField, Model), attribute.OptionLabel, attribute.HtmlAttributes) %>
<% }%>
<% else {%>
    <%= Html.DisplayForModel() %>
<% }%>

自定义DropDownListAttribute 属性

namespace mvc.Models
{
    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.ComponentModel.DataAnnotations;
    using System.Linq;
    using System.Web.Routing;

    [AttributeUsage(AttributeTargets.Property, AllowMultiple = false, Inherited = true)]
    public sealed class DropDownListAttribute : Attribute, ITemplateField
    {
        private static string defaultTemplateName;

        public DropDownListAttribute(string viewDataKey, string dataValueField) : this(viewDataKey, dataValueField, null)
        {
        }

        public DropDownListAttribute(string viewDataKey, string dataValueField, string dataTextField) : this(viewDataKey, dataValueField, dataTextField, null)
        {
        }

        public DropDownListAttribute(string viewDataKey, string dataValueField, string dataTextField, string optionLabel) : this(DefaultTemplateName, viewDataKey, dataValueField, dataTextField, optionLabel, null)
        {
        }

        public DropDownListAttribute(string viewDataKey, string dataValueField, string dataTextField, string optionLabel, object htmlAttributes) : this(DefaultTemplateName, viewDataKey, dataValueField, dataTextField, optionLabel, htmlAttributes)
        {
        }

        public DropDownListAttribute(string templateName, string viewDataKey, string dataValueField, string dataTextField, string optionLabel, object htmlAttributes)
        {
            if (string.IsNullOrEmpty(templateName))
            {
                throw new ArgumentException("Template name cannot be empty.");
            }

            if (string.IsNullOrEmpty(viewDataKey))
            {
                throw new ArgumentException("View data key cannot be empty.");
            }

            if (string.IsNullOrEmpty(dataValueField))
            {
                throw new ArgumentException("Data value field cannot be empty.");
            }

            TemplateName = templateName;
            ViewDataKey = viewDataKey;
            DataValueField = dataValueField;
            DataTextField = dataTextField;
            OptionLabel = optionLabel;
            HtmlAttributes = new RouteValueDictionary(htmlAttributes);
        }

        public static string DefaultTemplateName
        {
            get
            {
                if (string.IsNullOrEmpty(defaultTemplateName))
                {
                    defaultTemplateName = "DropDownList";
                }

                return defaultTemplateName;
            }
            set
            {
                defaultTemplateName = value;
            }
        }

        public string TemplateName { get; private set; }

        public string ViewDataKey { get; private set; }

        public string DataValueField { get; private set; }

        public string DataTextField { get; private set; }

        public string OptionLabel { get; private set; }

        public IDictionary<string, object> HtmlAttributes { get; private set; }

        public object GetSelectedValue(object model)
        {
            return GetPropertyValue(model, DataValueField);
        }

        public object GetSelectedText(object model)
        {
            return GetPropertyValue(model, !string.IsNullOrEmpty(DataTextField) ? DataTextField : DataValueField);
        }

        private static object GetPropertyValue(object model, string propertyName)
        {
            if (model != null)
            {
                PropertyDescriptor property = GetTypeDescriptor(model.GetType()).GetProperties()
                                                                                .Cast<PropertyDescriptor>()
                                                                                .SingleOrDefault(p => string.Compare(p.Name, propertyName, StringComparison.OrdinalIgnoreCase) == 0);
               
                if (property != null)
                {
                    return property.GetValue(model);
                }
            }

            return null;
        }

        private static ICustomTypeDescriptor GetTypeDescriptor(Type type)
        {
            return new AssociatedMetadataTypeTypeDescriptionProvider(type).GetTypeDescriptor(type);
        }
    }
}

自定义DataAnnotationsModelMetadata

public class FieldTemplateMetadata : DataAnnotationsModelMetadata
    {
        public FieldTemplateMetadata(DisplayAttribute aa, DataAnnotationsModelMetadataProvider provider, Type containerType, Func<object> modelAccessor, Type modelType, string propertyName, DisplayColumnAttribute displayColumnAttribute, IEnumerable<Attribute> attributes) : base(provider, containerType, modelAccessor, modelType, propertyName, displayColumnAttribute)
        {
            Attributes = new List<Attribute>(attributes);
            Display = aa;
        }

        public IList<Attribute> Attributes
        {
            get;
            private set;
        }
        public DisplayAttribute Display { get; set; }
    }

自定义 DataAnnotationsModelMetadataProvider

public class FieldTemplateMetadataProvider : DataAnnotationsModelMetadataProvider
    {
        protected override ModelMetadata CreateMetadata(IEnumerable<Attribute> attributes, Type containerType, Func<object> modelAccessor, Type modelType, string propertyName)
        {
            DataAnnotationsModelMetadata result = (DataAnnotationsModelMetadata) base.CreateMetadata(attributes, containerType, modelAccessor, modelType, propertyName);

            string templateName = attributes.OfType<ITemplateField>()
                                            .Select(field => field.TemplateName)
                                            .LastOrDefault();
            List<System.Attribute> attributeList = new List<System.Attribute>(attributes);
            DisplayAttribute disp = attributeList.OfType<DisplayAttribute>().FirstOrDefault();
            if (disp != null)
            {
                result.ShortDisplayName = disp.Order.ToString(); ;
                result.Description = disp.Description;
            }

           

            var data= (new FieldTemplateMetadata(disp, this, containerType, modelAccessor, modelType, propertyName, attributes.OfType<DisplayColumnAttribute>().FirstOrDefault(), attributes)

                    {
                        TemplateHint = !string.IsNullOrEmpty(templateName) ? templateName : result.TemplateHint,
                        HideSurroundingHtml = result.HideSurroundingHtml,
                        DataTypeName = result.DataTypeName,
                        IsReadOnly = result.IsReadOnly,
                        NullDisplayText = result.NullDisplayText,
                        DisplayFormatString = result.DisplayFormatString,
                        ConvertEmptyStringToNull = result.ConvertEmptyStringToNull,
                        EditFormatString = result.EditFormatString,
                        ShowForDisplay = result.ShowForDisplay,
                        ShowForEdit = result.ShowForEdit,
                        DisplayName = result.DisplayName,
                        Description = result.Description,
                        ShortDisplayName = result.ShortDisplayName,

                    });

            SearchFilterAttribute searchFilterAttribute = attributes.OfType<SearchFilterAttribute>().FirstOrDefault();
            if (searchFilterAttribute != null)
            {
                data.AdditionalValues.Add("Search", searchFilterAttribute);
            }

            OrderByAttribute orderByAttribute = attributes.OfType<OrderByAttribute>().FirstOrDefault();
            if (orderByAttribute != null)
            {
                data.AdditionalValues.Add("OrderBy", orderByAttribute);
            }
            return data;
        }
    }