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
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();
其他回答
结合顶部的答案创建一个匿名对象版本:
var queryString = HttpUtility2.BuildQueryString(new
{
key2 = "value2",
key1 = "value1",
});
这会产生这样的结果:
key2 = value2&key1 = value1
代码如下:
public static class HttpUtility2
{
public static string BuildQueryString<T>(T obj)
{
var queryString = HttpUtility.ParseQueryString(string.Empty);
foreach (var property in TypeDescriptor.GetProperties(typeof(T)).Cast<PropertyDescriptor>())
{
var value = (property.GetValue(obj) ?? "").ToString();
queryString.Add(property.Name, value);
}
return queryString.ToString();
}
}
我写了一些扩展方法，我发现在使用QueryStrings时非常有用。通常我想从当前的QueryString开始，并在使用它之前进行修改。类似的,
var res = Request.QueryString.Duplicate()
.ChangeField("field1", "somevalue")
.ChangeField("field2", "only if following is true", true)
.ChangeField("id", id, id>0)
.WriteLocalPathWithQuery(Request.Url)); //Uses context to write the path
欲了解更多信息，请访问:http://www.charlesrcook.com/archive/2008/07/23/c-extension-methods-for-asp.net-query-string-operations.aspx
很简单，但我喜欢这种风格。
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"));
在dotnet核心QueryHelpers.AddQueryString()将接受一个IDictionary<string,string>的键值对。为了节省一些内存分配和CPU周期，您可以使用SortedList<，>而不是Dictionary<，>，并按照排序顺序添加适当的容量和项…
var queryParams = new SortedList<string,string>(2);
queryParams.Add("abc", "val1");
queryParams.Add("def", "val2");
string requestUri = QueryHelpers.AddQueryString("https://localhost/api", queryParams);
这里有一种流畅的/lambda-ish方式作为扩展方法(结合了前面文章中的概念)，它支持对同一个键使用多个值。我个人更喜欢扩展，而不是包装，以便其他团队成员能够发现这类内容。请注意，关于编码方法存在争议，Stack Overflow(其中一篇)和MSDN博客上有很多关于它的帖子(比如这篇)。
public static string ToQueryString(this NameValueCollection source)
{
return String.Join("&", source.AllKeys
.SelectMany(key => source.GetValues(key)
.Select(value => String.Format("{0}={1}", HttpUtility.UrlEncode(key), HttpUtility.UrlEncode(value))))
.ToArray());
}
Edit: null支持，不过您可能需要根据您的特定情况对其进行调整
public static string ToQueryString(this NameValueCollection source, bool removeEmptyEntries)
{
return source != null ? String.Join("&", source.AllKeys
.Where(key => !removeEmptyEntries || source.GetValues(key)
.Where(value => !String.IsNullOrEmpty(value))
.Any())
.SelectMany(key => source.GetValues(key)
.Where(value => !removeEmptyEntries || !String.IsNullOrEmpty(value))
.Select(value => String.Format("{0}={1}", HttpUtility.UrlEncode(key), value != null ? HttpUtility.UrlEncode(value) : string.Empty)))
.ToArray())
: string.Empty;
}
