ASP.NET MVC Beta 新特性之IValueProvider -技术开发专区

ASP.NET MVC Beta 新特性之IValueProvider

作者：博客园编辑：胡铭娅 2009-02-20 14:20 来源：IT168�

要实现一个ValueProvider，我们只需要实现IValueProvider接口的GetValue方法，并且返回一个ValueProviderResult的结果就可以了。下面我们就写一个PostValueProvider来实现上面我们提出的情况。代码如下：

PostValueProvider
public class PostValueProvider : IValueProvider
{
    private ControllerContext context;
    //private DefaultValueProvider dProvider;

    public PostValueProvider(ControllerContext context)
    {
        this.context = context;
        //dProvider = new DefaultValueProvider(context);
    }

    #region IValueProvider 成员

    public ValueProviderResult GetValue(string name)
    {
        if (string.IsNullOrEmpty(name))
        {
            throw new ArgumentException("参数不能为空", "name");
        }
        switch (name)
        {
            case "Tags":
                return GetTagsValue();
            case "Categories":
                return GetCategoriesValue();
            default:
                return new DefaultValueProvider(context).GetValue(name);
        }
    }

    #endregion

    private ValueProviderResult GetTagsValue()
    {
        string strTags = GetValueFromRequest("Tags");
        if (string.IsNullOrEmpty(strTags))
        {
            return null;
        }

        string[] tags = strTags.Split(new string[] { "," }, StringSplitOptions.RemoveEmptyEntries);
        StateList<string> tagsList = new StateList<string>();
        foreach (string tag in tags)
        {
            tagsList.Add(tag.Trim().ToLowerInvariant());
        }

        return new ValueProviderResult(tagsList, strTags, CultureInfo.InvariantCulture);
    }

    private ValueProviderResult GetCategoriesValue()
    {
        string strCategories = GetValueFromRequest("Categories");
        if (string.IsNullOrEmpty(strCategories))
        {
            return null;
        }

        string[] categories = strCategories.Split(new string[] { "," }, StringSplitOptions.RemoveEmptyEntries);
        StateList<Category> list = new StateList<Category>();
        foreach (string c in categories)
        {
            list.Add(Category.GetCategory(new Guid(c)));
        }

        return new ValueProviderResult(list, strCategories, CultureInfo.InvariantCulture);
    }

    private string GetValueFromRequest(string name)
    {
        string value = null;
        HttpRequestBase request = context.HttpContext.Request;
        if (request != null)
        {
            if (request.QueryString != null)
            {
                value = request.QueryString[name];
            }
            if (string.IsNullOrEmpty(value) && (request.Form != null))
            {
                value = request.Form[name];
            }
        }

        return value;
    }
}

然后我们就可以在UpdateModel方法中使用我们的PostValueProvider了：

/// <summary>
/// 将提交过来的新随笔表单内容保存到数据库
/// </summary>
[AcceptVerbs("POST"), ActionName("NewPost")]
public ActionResult SaveNewPost(FormCollection form)
{
    Post post = new Post();
    try
    {
        UpdateModel(post, new[] { "Title", "Content", "Slug", "Tags", "Categories" }, new PostValueProvider(ControllerContext));
    }
    catch
    {
        return View(post);
    }

   ..
}

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