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
HttpValueCollection的可链接包装类:
namespace System.Web.Mvc {
public class QueryStringBuilder {
private NameValueCollection collection;
public QueryStringBuilder() {
collection = System.Web.HttpUtility.ParseQueryString(string.Empty);
}
public QueryStringBuilder Add(string key, string value) {
collection.Add(key, value);
return this;
}
public QueryStringBuilder Remove(string key) {
collection.Remove(key);
return this;
}
public string this[string key] {
get { return collection[key]; }
set { collection[key] = value; }
}
public string ToString() {
return collection.ToString();
}
}
}
使用示例:
QueryStringBuilder parameters = new QueryStringBuilder()
.Add("view", ViewBag.PageView)
.Add("page", ViewBag.PageNumber)
.Add("size", ViewBag.PageSize);
string queryString = parameters.ToString();
其他回答
我为我的剃刀项目写了一个助手，使用了其他答案的一些提示。
ParseQueryString业务是必要的，因为我们不允许篡改当前请求的QueryString对象。
@helper GetQueryStringWithValue(string key, string value) {
var queryString = System.Web.HttpUtility.ParseQueryString(HttpContext.Current.Request.QueryString.ToString());
queryString[key] = value;
@Html.Raw(queryString.ToString())
}
我是这样使用的:
location.search = '?@Helpers.GetQueryStringWithValue("var-name", "var-value")';
如果希望它接受多个值，只需将参数更改为Dictionary，并将对添加到查询字符串中。
我需要为我正在开发的可移植类库(PCL)解决同样的问题。在这种情况下，我没有访问系统的权限。所以我不能用ParseQueryString。
相反，我使用System.Net.Http.FormUrlEncodedContent像这样:
var url = new UriBuilder("http://example.com");
url.Query = new FormUrlEncodedContent(new Dictionary<string,string>()
{
{"param1", "val1"},
{"param2", "val2"},
{"param3", "val3"},
}).ReadAsStringAsync().Result;
我有一个扩展方法的Uri:
接受匿名对象:uri。WithQuery(new {name = "value"}) 接受字符串/字符串对的集合(例如Dictionary ' 2)。 接受字符串/对象对的集合(例如RouteValueDictionary)。 接受NameValueCollections。 按键对查询值进行排序，以便相同的值产生相同的uri。 每个键支持多个值，保持其原始顺序。
文档版本可以在这里找到。
扩展:
public static Uri WithQuery(this Uri uri, object values)
{
if (uri == null)
throw new ArgumentNullException(nameof(uri));
if (values != null)
{
var query = string.Join(
"&", from p in ParseQueryValues(values)
where !string.IsNullOrWhiteSpace(p.Key)
let k = HttpUtility.UrlEncode(p.Key.Trim())
let v = HttpUtility.UrlEncode(p.Value)
orderby k
select string.IsNullOrEmpty(v) ? k : $"{k}={v}");
if (query.Length != 0 || uri.Query.Length != 0)
uri = new UriBuilder(uri) { Query = query }.Uri;
}
return uri;
}
查询解析器:
private static IEnumerable<KeyValuePair<string, string>> ParseQueryValues(object values)
{
// Check if a name/value collection.
var nvc = values as NameValueCollection;
if (nvc != null)
return from key in nvc.AllKeys
from val in nvc.GetValues(key)
select new KeyValuePair<string, string>(key, val);
// Check if a string/string dictionary.
var ssd = values as IEnumerable<KeyValuePair<string, string>>;
if (ssd != null)
return ssd;
// Check if a string/object dictionary.
var sod = values as IEnumerable<KeyValuePair<string, object>>;
if (sod == null)
{
// Check if a non-generic dictionary.
var ngd = values as IDictionary;
if (ngd != null)
sod = ngd.Cast<dynamic>().ToDictionary<dynamic, string, object>(
p => p.Key.ToString(), p => p.Value as object);
// Convert object properties to dictionary.
if (sod == null)
sod = new RouteValueDictionary(values);
}
// Normalize and return the values.
return from pair in sod
from val in pair.Value as IEnumerable<string>
?? new[] { pair.Value?.ToString() }
select new KeyValuePair<string, string>(pair.Key, val);
}
下面是测试:
var uri = new Uri("https://stackoverflow.com/yo?oldKey=oldValue");
// Test with a string/string dictionary.
var q = uri.WithQuery(new Dictionary<string, string>
{
["k1"] = string.Empty,
["k2"] = null,
["k3"] = "v3"
});
Debug.Assert(q == new Uri(
"https://stackoverflow.com/yo?k1&k2&k3=v3"));
// Test with a string/object dictionary.
q = uri.WithQuery(new Dictionary<string, object>
{
["k1"] = "v1",
["k2"] = new[] { "v2a", "v2b" },
["k3"] = null
});
Debug.Assert(q == new Uri(
"https://stackoverflow.com/yo?k1=v1&k2=v2a&k2=v2b&k3"));
// Test with a name/value collection.
var nvc = new NameValueCollection()
{
["k1"] = string.Empty,
["k2"] = "v2a"
};
nvc.Add("k2", "v2b");
q = uri.WithQuery(nvc);
Debug.Assert(q == new Uri(
"https://stackoverflow.com/yo?k1&k2=v2a&k2=v2b"));
// Test with any dictionary.
q = uri.WithQuery(new Dictionary<int, HashSet<string>>
{
[1] = new HashSet<string> { "v1" },
[2] = new HashSet<string> { "v2a", "v2b" },
[3] = null
});
Debug.Assert(q == new Uri(
"https://stackoverflow.com/yo?1=v1&2=v2a&2=v2b&3"));
// Test with an anonymous object.
q = uri.WithQuery(new
{
k1 = "v1",
k2 = new[] { "v2a", "v2b" },
k3 = new List<string> { "v3" },
k4 = true,
k5 = null as Queue<string>
});
Debug.Assert(q == new Uri(
"https://stackoverflow.com/yo?k1=v1&k2=v2a&k2=v2b&k3=v3&k4=True&k5"));
// Keep existing query using a name/value collection.
nvc = HttpUtility.ParseQueryString(uri.Query);
nvc.Add("newKey", "newValue");
q = uri.WithQuery(nvc);
Debug.Assert(q == new Uri(
"https://stackoverflow.com/yo?newKey=newValue&oldKey=oldValue"));
// Merge two query objects using the RouteValueDictionary.
var an1 = new { k1 = "v1" };
var an2 = new { k2 = "v2" };
q = uri.WithQuery(
new RouteValueDictionary(an1).Concat(
new RouteValueDictionary(an2)));
Debug.Assert(q == new Uri(
"https://stackoverflow.com/yo?k1=v1&k2=v2"));
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();
}
将这个类添加到项目中
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
public class QueryStringBuilder
{
private readonly List<KeyValuePair<string, object>> _list;
public QueryStringBuilder()
{
_list = new List<KeyValuePair<string, object>>();
}
public void Add(string name, object value)
{
_list.Add(new KeyValuePair<string, object>(name, value));
}
public override string ToString()
{
return String.Join("&", _list.Select(kvp => String.Concat(Uri.EscapeDataString(kvp.Key), "=", Uri.EscapeDataString(kvp.Value.ToString()))));
}
}
像这样使用它:
var actual = new QueryStringBuilder {
{"foo", 123},
{"bar", "val31"},
{"bar", "val32"}
};
actual.Add("a+b", "c+d");
actual.ToString(); // "foo=123&bar=val31&bar=val32&a%2bb=c%2bd"
