当从代码中调用web资源时，一个常见的任务是构建一个包含所有必要参数的查询字符串。虽然这绝不是火箭科学，但有一些漂亮的细节需要注意，例如，如果不是第一个参数，则添加&，对参数进行编码等。
实现它的代码非常简单，但有点乏味:
StringBuilder SB = new StringBuilder();
if (NeedsToAddParameter A)
{
SB.Append("A="); SB.Append(HttpUtility.UrlEncode("TheValueOfA"));
}
if (NeedsToAddParameter B)
{
if (SB.Length>0) SB.Append("&");
SB.Append("B="); SB.Append(HttpUtility.UrlEncode("TheValueOfB")); }
}
这是一个非常常见的任务，人们希望存在一个实用工具类，使其更加优雅和可读。扫描MSDN，我没有找到一个，这让我想到了以下问题:
你所知道的最优雅干净的方法是什么?
当前回答
你可以通过调用system . web . httputiity . parsequerystring (string.Empty)来创建一个新的可写的HttpValueCollection实例，然后将它用作任何NameValueCollection。一旦你添加了你想要的值，你可以在集合上调用ToString来获得一个查询字符串，如下所示:
NameValueCollection queryString = System.Web.HttpUtility.ParseQueryString(string.Empty);
queryString.Add("key1", "value1");
queryString.Add("key2", "value2");
return queryString.ToString(); // Returns "key1=value1&key2=value2", all URL-encoded
HttpValueCollection是内部的，所以你不能直接构造一个实例。然而，一旦你获得了一个实例，你就可以像使用其他NameValueCollection一样使用它。因为你正在使用的实际对象是一个HttpValueCollection，调用ToString方法将调用HttpValueCollection上的重写方法，它将集合格式化为url编码的查询字符串。
在SO和网络上搜索类似问题的答案后，这是我能找到的最简单的解决方案。
net核心
如果你在。net Core中工作，你可以使用Microsoft.AspNetCore.WebUtilities.QueryHelpers类，它极大地简化了这一点。
https://learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.webutilities.queryhelpers
示例代码:
const string url = "https://customer-information.azure-api.net/customers/search/taxnbr";
var param = new Dictionary<string, string>() { { "CIKey", "123456789" } };
var newUrl = new Uri(QueryHelpers.AddQueryString(url, param));
其他回答
public static string ToQueryString(this Dictionary<string, string> source)
{
return String.Join("&", source.Select(kvp => String.Format("{0}={1}", HttpUtility.UrlEncode(kvp.Key), HttpUtility.UrlEncode(kvp.Value))).ToArray());
}
public static string ToQueryString(this NameValueCollection source)
{
return String.Join("&", source.Cast<string>().Select(key => String.Format("{0}={1}", HttpUtility.UrlEncode(key), HttpUtility.UrlEncode(source[key]))).ToArray());
}
下面是一个使用非常基本的语言特性的实现。它是我们必须在Objective C中移植和维护的类的一部分，所以我们选择了更多的代码行，但更容易移植和理解不太熟悉c#的程序员。
/// <summary>
/// Builds a complete http url with query strings.
/// </summary>
/// <param name="pHostname"></param>
/// <param name="pPort"></param>
/// <param name="pPage">ex "/index.html" or index.html</param>
/// <param name="pGetParams">a Dictionary<string,string> collection containing the key value pairs. Pass null if there are none.</param>
/// <returns>a string of the form: http://[pHostname]:[pPort/[pPage]?key1=val1&key2=val2...</returns>
static public string buildURL(string pHostname, int pPort, string pPage, Dictionary<string,string> pGetParams)
{
StringBuilder sb = new StringBuilder(200);
sb.Append("http://");
sb.Append(pHostname);
if( pPort != 80 ) {
sb.Append(pPort);
}
// Allows page param to be passed in with or without leading slash.
if( !pPage.StartsWith("/") ) {
sb.Append("/");
}
sb.Append(pPage);
if (pGetParams != null && pGetParams.Count > 0)
{
sb.Append("?");
foreach (KeyValuePair<string, string> kvp in pGetParams)
{
sb.Append(kvp.Key);
sb.Append("=");
sb.Append( System.Web.HttpUtility.UrlEncode(kvp.Value) );
sb.Append("&");
}
sb.Remove(sb.Length - 1, 1); // Remove the final '&'
}
return sb.ToString();
}
只针对那些需要VB的人。NET版本的顶级答案:
Public Function ToQueryString(nvc As System.Collections.Specialized.NameValueCollection) As String
Dim array As String() = nvc.AllKeys.SelectMany(Function(key As String) nvc.GetValues(key), Function(key As String, value As String) String.Format("{0}={1}", System.Web.HttpUtility.UrlEncode(key), System.Web.HttpUtility.UrlEncode(value))).ToArray()
Return "?" + String.Join("&", array)
End Function
以及没有LINQ的版本:
Public Function ToQueryString(nvc As System.Collections.Specialized.NameValueCollection) As String
Dim lsParams As New List(Of String)()
For Each strKey As String In nvc.AllKeys
Dim astrValue As String() = nvc.GetValues(strKey)
For Each strValue As String In astrValue
lsParams.Add(String.Format("{0}={1}", System.Web.HttpUtility.UrlEncode(strKey), System.Web.HttpUtility.UrlEncode(strValue)))
Next ' Next strValue
Next ' strKey
Dim astrParams As String() = lsParams.ToArray()
lsParams.Clear()
lsParams = Nothing
Return "?" + String.Join("&", astrParams)
End Function ' ToQueryString
和没有LINQ的c#版本:
public static string ToQueryString(System.Collections.Specialized.NameValueCollection nvc)
{
List<string> lsParams = new List<string>();
foreach (string strKey in nvc.AllKeys)
{
string[] astrValue = nvc.GetValues(strKey);
foreach (string strValue in astrValue)
{
lsParams.Add(string.Format("{0}={1}", System.Web.HttpUtility.UrlEncode(strKey), System.Web.HttpUtility.UrlEncode(strValue)));
} // Next strValue
} // Next strKey
string[] astrParams =lsParams.ToArray();
lsParams.Clear();
lsParams = null;
return "?" + string.Join("&", astrParams);
} // End Function ToQueryString
从Roy Tinker的评论中得到灵感，我最终在Uri类上使用了一个简单的扩展方法，使我的代码简洁干净:
using System.Web;
public static class HttpExtensions
{
public static Uri AddQuery(this Uri uri, string name, string value)
{
var httpValueCollection = HttpUtility.ParseQueryString(uri.Query);
httpValueCollection.Remove(name);
httpValueCollection.Add(name, value);
var ub = new UriBuilder(uri);
ub.Query = httpValueCollection.ToString();
return ub.Uri;
}
}
用法:
Uri url = new Uri("http://localhost/rest/something/browse").
AddQuery("page", "0").
AddQuery("pageSize", "200");
编辑-标准兼容的变体
正如一些人指出的那样，httpValueCollection.ToString()以一种不符合标准的方式编码Unicode字符。这是通过调用HttpUtility来处理此类字符的相同扩展方法的变体。UrlEncode方法代替已弃用的HttpUtility方法。UrlEncodeUnicode方法。
using System.Web;
public static Uri AddQuery(this Uri uri, string name, string value)
{
var httpValueCollection = HttpUtility.ParseQueryString(uri.Query);
httpValueCollection.Remove(name);
httpValueCollection.Add(name, value);
var ub = new UriBuilder(uri);
// this code block is taken from httpValueCollection.ToString() method
// and modified so it encodes strings with HttpUtility.UrlEncode
if (httpValueCollection.Count == 0)
ub.Query = String.Empty;
else
{
var sb = new StringBuilder();
for (int i = 0; i < httpValueCollection.Count; i++)
{
string text = httpValueCollection.GetKey(i);
{
text = HttpUtility.UrlEncode(text);
string val = (text != null) ? (text + "=") : string.Empty;
string[] vals = httpValueCollection.GetValues(i);
if (sb.Length > 0)
sb.Append('&');
if (vals == null || vals.Length == 0)
sb.Append(val);
else
{
if (vals.Length == 1)
{
sb.Append(val);
sb.Append(HttpUtility.UrlEncode(vals[0]));
}
else
{
for (int j = 0; j < vals.Length; j++)
{
if (j > 0)
sb.Append('&');
sb.Append(val);
sb.Append(HttpUtility.UrlEncode(vals[j]));
}
}
}
}
}
ub.Query = sb.ToString();
}
return ub.Uri;
}
这与公认的答案完全相同，只是稍微更紧凑:
private string ToQueryString(NameValueCollection nvc)
{
return "?" + string.Join("&", nvc.AllKeys.Select(k => string.Format("{0}={1}",
HttpUtility.UrlEncode(k),
HttpUtility.UrlEncode(nvc[k]))));
}
