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

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

其他回答

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"

这是另一种(可能是多余的:-])方法。

其概念与本页的《吠陀经》答案相同(请看这里)。

但是这个类更有效,因为它只迭代所有key一次:当调用ToString时。

格式化代码也进行了简化和改进。

希望对大家有所帮助。

public sealed class QueryStringBuilder
{
    public QueryStringBuilder()
    {
        this.inner = HttpUtility.ParseQueryString(string.Empty);
    }

    public QueryStringBuilder(string queryString)
    {
        this.inner = HttpUtility.ParseQueryString(queryString);
    }

    public QueryStringBuilder(string queryString, Encoding encoding)
    {
        this.inner = HttpUtility.ParseQueryString(queryString, encoding);
    }

    private readonly NameValueCollection inner;

    public QueryStringBuilder AddKey(string key, string value)
    {
        this.inner.Add(key, value);
        return this;
    }

    public QueryStringBuilder RemoveKey(string key)
    {
        this.inner.Remove(key);
        return this;
    }

    public QueryStringBuilder Clear()
    {
        this.inner.Clear();
        return this;
    }

    public override String ToString()
    {
        if (this.inner.Count == 0)
            return string.Empty;

        var builder = new StringBuilder();

        for (int i = 0; i < this.inner.Count; i++)
        {
            if (builder.Length > 0)
                builder.Append('&');

            var key = this.inner.GetKey(i);
            var values = this.inner.GetValues(i);

            if (key == null || values == null || values.Length == 0)
                continue;

            for (int j = 0; j < values.Length; j++)
            {
                if (j > 0)
                    builder.Append('&');

                builder.Append(HttpUtility.UrlEncode(key));
                builder.Append('=');
                builder.Append(HttpUtility.UrlEncode(values[j]));
            }
        }

        return builder.ToString();
    }
}

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();
    }
}

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]))));
}

只是想说说我的看法

public static class HttpClientExt
{
    public static Uri AddQueryParams(this Uri uri, string query)
    {
        var ub = new UriBuilder(uri);
        ub.Query = string.IsNullOrEmpty(uri.Query) ? query : string.Join("&", uri.Query.Substring(1), query);
        return ub.Uri;
    }

    public static Uri AddQueryParams(this Uri uri, IEnumerable<string> query)
    {
        return uri.AddQueryParams(string.Join("&", query));
    } 

    public static Uri AddQueryParams(this Uri uri, string key, string value)
    {
        return uri.AddQueryParams(string.Join("=", HttpUtility.UrlEncode(key), HttpUtility.UrlEncode(value)));
    }

    public static Uri AddQueryParams(this Uri uri, params KeyValuePair<string,string>[] kvps)
    {
        return uri.AddQueryParams(kvps.Select(kvp => string.Join("=", HttpUtility.UrlEncode(kvp.Key), HttpUtility.UrlEncode(kvp.Value))));
    }

    public static Uri AddQueryParams(this Uri uri, IDictionary<string, string> kvps)
    {
        return uri.AddQueryParams(kvps.Select(kvp => string.Join("=", HttpUtility.UrlEncode(kvp.Key), HttpUtility.UrlEncode(kvp.Value))));
    }

    public static Uri AddQueryParams(this Uri uri, NameValueCollection nvc)
    {
        return uri.AddQueryParams(nvc.AllKeys.SelectMany(nvc.GetValues, (key, value) => string.Join("=", HttpUtility.UrlEncode(key), HttpUtility.UrlEncode(value))));
    }
}

文档说uri。查询将以?如果它是非空的,如果你要修改它,你应该把它剪掉。

注意HttpUtility。UrlEncode可以在System.Web中找到。

用法:

var uri = new Uri("https://api.del.icio.us/v1/posts/suggest").AddQueryParam("url","http://stackoverflow.com")