与罗斯托夫的帖子一样，如果你不想包含对系统的引用。在你的项目中，你可以使用System.Net.Http.Formatting中的FormDataCollection，然后做如下的事情:

使用System.Net.Http.Formatting.FormDataCollection

var parameters = new Dictionary<string, string>()
{
    { "ham", "Glaced?" },
    { "x-men", "Wolverine + Logan" },
    { "Time", DateTime.UtcNow.ToString() },
}; 
var query = new FormDataCollection(parameters).ReadAsNameValueCollection().ToString();

对于那些不想包括系统。Web在项目中还没有使用它，你可以使用System.Net.Http的FormUrlEncodedContent，并做如下的事情:

keyvaluepair版本

string query;
using(var content = new FormUrlEncodedContent(new KeyValuePair<string, string>[]{
    new KeyValuePair<string, string>("ham", "Glazed?"),
    new KeyValuePair<string, string>("x-men", "Wolverine + Logan"),
    new KeyValuePair<string, string>("Time", DateTime.UtcNow.ToString()),
})) {
    query = content.ReadAsStringAsync().Result;
}

字典的版本

string query;
using(var content = new FormUrlEncodedContent(new Dictionary<string, string>()
{
    { "ham", "Glaced?"},
    { "x-men", "Wolverine + Logan"},
    { "Time", DateTime.UtcNow.ToString() },
})) {
    query = content.ReadAsStringAsync().Result;
}

如果我想使用System.Net.HttpClient提交一个http get请求 似乎没有API来添加参数，这是正确的吗?

Yes.

是否有任何简单的api可用来构建查询字符串 不涉及构建名称值集合和url编码 然后最后把它们连接起来?

肯定的:

var query = HttpUtility.ParseQueryString(string.Empty);
query["foo"] = "bar<>&-baz";
query["bar"] = "bazinga";
string queryString = query.ToString();

会给你预期的结果:

foo=bar%3c%3e%26-baz&bar=bazinga

你可能还会发现UriBuilder类很有用:

var builder = new UriBuilder("http://example.com");
builder.Port = -1;
var query = HttpUtility.ParseQueryString(builder.Query);
query["foo"] = "bar<>&-baz";
query["bar"] = "bazinga";
builder.Query = query.ToString();
string url = builder.ToString();

会给你预期的结果:

http://example.com/?foo=bar%3c%3e%26-baz&bar=bazinga

你可以非常安全地将它提供给HttpClient。GetAsync方法。

HttpClient client = new HttpClient();
var uri = Environment.GetEnvironmentVariable("URL of Api");
                
var requesturi = QueryHelpers.AddQueryString(uri, "parameter_name",parameter_value);
client.BaseAddress = new Uri(requesturi);

然后你也可以添加请求头例如:

client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
client.DefaultRequestHeaders.Add("x-api-key", secretValue);

响应语法eg:

HttpResponseMessage response = client.GetAsync(requesturi).Result;

希望它对你有用。

Darin提供了一个有趣而聪明的解决方案，这里有一些可能是另一个选择:

public class ParameterCollection
{
    private Dictionary<string, string> _parms = new Dictionary<string, string>();

    public void Add(string key, string val)
    {
        if (_parms.ContainsKey(key))
        {
            throw new InvalidOperationException(string.Format("The key {0} already exists.", key));
        }
        _parms.Add(key, val);
    }

    public override string ToString()
    {
        var server = HttpContext.Current.Server;
        var sb = new StringBuilder();
        foreach (var kvp in _parms)
        {
            if (sb.Length > 0) { sb.Append("&"); }
            sb.AppendFormat("{0}={1}",
                server.UrlEncode(kvp.Key),
                server.UrlEncode(kvp.Value));
        }
        return sb.ToString();
    }
}

所以当你使用它时，你可以这样做:

var parms = new ParameterCollection();
parms.Add("key", "value");

var url = ...
url += "?" + parms;

或者简单地使用我的Uri扩展

Code

public static Uri AttachParameters(this Uri uri, NameValueCollection parameters)
{
    var stringBuilder = new StringBuilder();
    string str = "?";
    for (int index = 0; index < parameters.Count; ++index)
    {
        stringBuilder.Append(str + parameters.AllKeys[index] + "=" + parameters[index]);
        str = "&";
    }
    return new Uri(uri + stringBuilder.ToString());
}

使用

Uri uri = new Uri("http://www.example.com/index.php").AttachParameters(new NameValueCollection
                                                                           {
                                                                               {"Bill", "Gates"},
                                                                               {"Steve", "Jobs"}
                                                                           });

结果

http://www.example.com/index.php?Bill=Gates&Steve=Jobs