一行代码搞定你的QueryString(转)

初级阶段
为每个QueryString写转换的代码，针对不同的类型，进行转换和错误处理。

中级阶段
写了一个函数，专门做转换（1.1里写的）：

/// <summary>
/// Convert query string to parameter.
/// </summary>
/// <param name="name">Name of query string</param>
/// <param name="defaultValue">Default value of query string</param>
/// <param name="isRequired">If the query string is required</param>
private object ConvertParameter(string name, object defaultValue, bool isRequired)

高级阶段
昨天写的，第一次发文，大家拍砖吧：

主要是用了Attribute和反射的思想，首先给变量设置HttpQueryString的属性，绑定上相应的QueryString，然后由Page基类来读取相应的QueryString信息。

属性这么写（HttpQueryStringAttribute.cs）：

using System;

namespace GooKuu.Framework.Web
{

/// <summary>
/// Specifies a field for a query string.
/// </summary>
[AttributeUsage(AttributeTargets.Field)]
public sealed class HttpQueryStringAttribute : Attribute
{
private string _name;
private object _defaultValue;
private bool _isRequired;

/// <summary>
/// Constructor. The query string must be provided.
/// </summary>
/// <param name="name">Name of the query string</param>
public HttpQueryStringAttribute(string name)
{
_name = name;
_defaultValue = null;
_isRequired = true;
}

/// <summary>
/// Constructor. If the query string is not be provided, using the default value.
/// </summary>
/// <param name="name">Name of the query string</param>
/// <param name="defaultValue">Default value of the query string which is not provided</param>
public HttpQueryStringAttribute(string name, object defaultValue)
{
_name = name;
_defaultValue = defaultValue;
_isRequired = false;
}

/// <summary>
/// Name of the query string.
/// </summary>
public string Name
{
get { return _name; }
}

/// <summary>
/// Default value of the query string which is not provided.
/// </summary>
public object DefaultValue
{
get { return _defaultValue; }
}

/// <summary>
/// Indicates if the query string must be provided.
/// </summary>
public bool IsRequired
{
get { return _isRequired; }
}
}
}

页面基类是这样的（PageBase.cs）：

using System;
using System.Reflection;
using System.Web;
using System.Web.UI;

namespace GooKuu.Framework.Web
{
/// <summary>
/// Base class of all pages.
/// </summary>
public class PageBase : Page
{
/// <summary>
/// Override OnLoad method of base class.
/// </summary>
/// <param name="e"></param>
protected override void OnLoad(System.EventArgs e)
{
ParameterInitialize();
base.OnLoad(e);
}

/// <summary>
/// Initialize parameters according to query strings.
/// </summary>
private void ParameterInitialize()
{
// Get Type of current page class.
Type type = this.GetType();

// Get all fields of current page class.
FieldInfo[] fields = type.GetFields();

foreach (FieldInfo field in fields)
{
// Get HttpQueryStringAttribute of current field.
HttpQueryStringAttribute attribute = (HttpQueryStringAttribute)Attribute.GetCustomAttribute(field, typeof(HttpQueryStringAttribute));

// If has HttpQueryStringAttribute, this field is for a query string.
if (attribute != null)
{
SetField(field, attribute);
}
}
}

/// <summary>
/// Set field according to the HttpQueryStringAttribute.
/// </summary>
/// <param name="field">The field will be set</param>
/// <param name="attribute">The attribute of current field</param>
private void SetField(FieldInfo field, HttpQueryStringAttribute attribute)
{
// The query string must be provided.
if (attribute.IsRequired)
{
if (Request.QueryString[attribute.Name] != null)
{
SetFieldValue(field, this, attribute.Name, field.FieldType);
}
else
{
throw new Exception(string.Format("Query string /"{0}/" is required", attribute.Name), new NullReferenceException());
}
}
// If the query string is not be provided, using the default value.
else
{
if (attribute.DefaultValue == null || field.FieldType == attribute.DefaultValue.GetType())
{
if (Request.QueryString[attribute.Name] == null || Request.QueryString[attribute.Name] == string.Empty)
{
field.SetValue(this, attribute.DefaultValue);
}
else
{
SetFieldValue(field, this, attribute.Name, field.FieldType);
}
}
else
{
throw new Exception(string.Format("Invalid default value of query string /"{0}/"({1})", attribute.Name, field.Name), new NullReferenceException());
}
}
}

/// <summary>
/// Set the value of current field according to the query string.
/// </summary>
/// <param name="field">The field will be set</param>
/// <param name="obj">The object whose field value will be set</param>
/// <param name="name">The name of query string</param>
/// <param name="conversionType">The type to be converted</param>
private void SetFieldValue(FieldInfo field, object obj, string name, Type conversionType)
{
try
{
// Set field value.
field.SetValue(obj, Convert.ChangeType(Request.QueryString[name], conversionType));
}
catch (Exception ex)
{
throw new Exception(string.Format("The given value of query string /"{0}/" can not be convert to {1}", name, conversionType), ex);
}
}
}
}

在页面里，这样写就OK了（Default.aspx.cs）：

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using GooKuu.Framework.Web;

public partial class _Default : PageBase
{

/// <summary>
/// Name 是Query String的名字，"Anonymous"是缺省值。
/// 如果没有提供这个Query String，就采用缺省值。
/// </summary>
[HttpQueryString("Name", "Anonymous")]
public string name;

/// <summary>
/// UserId 是Query String的名字，不提供缺省值。
/// 如果没有提供这个Query String或者提供的格式不正确导致转换失败，都会抛出异常。
/// </summary>
[HttpQueryString("UserId")]
public int userId;

protected void Page_Load(object sender, EventArgs e)
{
Response.Write(string.Format("Name is {0}<br/>", name));
Response.Write(string.Format("UserId is {0}<br/>", userId));
}
}

[ 日期：2006-01-18 ] [ 来自：Ariel Y ]