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?
未经测试,但我认为沿着这些路线的东西会工作得很好
public class QueryString
{
private Dictionary<string,string> _Params = new Dictionary<string,string>();
public overide ToString()
{
List<string> returnParams = new List<string>();
foreach (KeyValuePair param in _Params)
{
returnParams.Add(String.Format("{0}={1}", param.Key, param.Value));
}
// return String.Format("?{0}", String.Join("&", returnParams.ToArray()));
// credit annakata
return "?" + String.Join("&", returnParams.ToArray());
}
public void Add(string key, string value)
{
_Params.Add(key, HttpUtility.UrlEncode(value));
}
}
QueryString query = new QueryString();
query.Add("param1", "value1");
query.Add("param2", "value2");
return query.ToString();
基于扩展方法的快速版本:
class Program
{
static void Main(string[] args)
{
var parameters = new List<KeyValuePair<string, string>>
{
new KeyValuePair<string, string>("A", "AValue"),
new KeyValuePair<string, string>("B", "BValue")
};
string output = "?" + string.Join("&", parameters.ConvertAll(param => param.ToQueryString()).ToArray());
}
}
public static class KeyValueExtensions
{
public static string ToQueryString(this KeyValuePair<string, string> obj)
{
return obj.Key + "=" + HttpUtility.UrlEncode(obj.Value);
}
}
可以使用where子句来选择将哪些参数添加到字符串中。
适用于NameValueCollection中每个键的多个值。
例:{{“k1”、“v1”},{“k1”、“v1”}}= > ? k1 = v1&k1 = v1
/// <summary>
/// Get query string for name value collection.
/// </summary>
public static string ToQueryString(this NameValueCollection collection,
bool prefixQuestionMark = true)
{
collection.NullArgumentCheck();
if (collection.Keys.Count == 0)
{
return "";
}
var buffer = new StringBuilder();
if (prefixQuestionMark)
{
buffer.Append("?");
}
var append = false;
for (int i = 0; i < collection.Keys.Count; i++)
{
var key = collection.Keys[i];
var values = collection.GetValues(key);
key.NullCheck();
values.NullCheck();
foreach (var value in values)
{
if (append)
{
buffer.Append("&");
}
append = true;
buffer.AppendFormat("{0}={1}", key.UrlEncode(), value.UrlEncode());
}
}
return buffer.ToString();
}
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();
}