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xamarin android中网络请求的框架非常多，在项目中使用的是第三方的一个网络请求框架restsharp，应该是github上.net网络请求最多star的框架，没有之一。这里就简单汇总了其他的一些网络请求的例子，主要还是分为android和.net两种平台。
下面就用.net中的httpwebrequest、httpclient、restsharp和android中的httpURLConnection、okhttp实现一个get方式获取图片、post方式提交表单，适合新手入门看看总结一下。
效果图如下：
1.HttpWebRquest、HttpWebResponse
命名空间: System.Net；程序集: System（位于 System.dll）
public class HttpWebRequestUtil
{
//发送get请求获取bytes
public static async System.Threading.Tasks.Task<byte[]> GetBytes(string path)
{
try
{
HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(path);
request.Method = "get";
request.Timeout = 500;
//request.Proxy设置代理
//path 中可添加querystring参数
//request.UserAgent 请求的代理
HttpWebResponse response = (HttpWebResponse)await request.GetResponseAsync();
if (response.StatusCode == HttpStatusCode.OK)
{
Stream responseStream = response.GetResponseStream();
//将流转成字节
byte[] bytes = StreamUtil.StreamToBytes(responseStream);
return bytes;
}
else
return null;
}
catch (Exception ex)
{
return null;
}
}
public static async System.Threading.Tasks.Task<bool> PostForm(string path, string name, string pwd)
{
try
{
string formData = "name=" + name +"&pwd=" +pwd ;
byte[] bytes = Encoding.UTF8.GetBytes(formData);
StringBuilder strBuilder = new StringBuilder();
HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(path);
request.Method = "get";
request.Timeout = 500;
request.ContentType = "application/x-www-form-urlencoded; charset=UTF-8";
request.ContentLength = bytes.Length;
request.Method = "Post";
Stream requestStream = request.GetRequestStream();
requestStream.Write(bytes, 0, bytes.Length);
requestStream.Close();
HttpWebResponse response = (HttpWebResponse)await request.GetResponseAsync();
if (response.StatusCode == HttpStatusCode.OK)
{
StreamReader streamReader = new StreamReader(response.GetResponseStream(), Encoding.UTF8);
string content = JsonConvert.DeserializeObject<string>(streamReader.ReadToEnd());
streamReader.Close();
if (content == "success")
{
return true;
}
else
return false;
}
return false;
}
catch (Exception ex)
{
return false;
}
}
}2.RestSharp .net常用的http网络请求库
当然重点还是说一下这个的。restsharp在github上的star应该是.net网络请求库最多的，（和第二名的差距比较大）。可以在nuget上直接添加引用restsharp。
github地址：https://github.com/restsharp/RestSharp
restSharp官网：http://restsharp.org/
stackoverflow上restsharp的相关问题汇总： https://stackoverflow.com/questions/tagged/RestSharp
restsharp有一下这么几个重要的有点：
- 轻量级的、基于HttpWebRequest的封装（不依赖任何第三方组件、支持.net 任何平台上）
- 支持异步操作、支持http的get、post、put、delete等操作
- 使用简单、易调试、request和response的类型齐全
- 功能齐全，支持oAuth 1, oAuth 2, Basic等授权验证、可上传文件
- 自定义序列化和反序列化、自动检测返回的内容类型
public class RestSharpUtil
{
internal static RestClient Instance(string url)
{
var restClient = new RestClient(url)
{
Timeout = 5000,
ReadWriteTimeout = 5000
};
return restClient;
}
public static async System.Threading.Tasks.Task<bool> Post(string url, User user)
{
RestClient restClient = Instance(url);
RestRequest request = new RestRequest();
//request.AddQueryParameter("id","") 添加url的参数(AddUrlSegment)
//request.AddHeader("Authorization","token");添加请求头参数
// request.AddHeader("content-type", "application/x-www-form-urlencoded; charset=UTF-8");
request.AddJsonBody(user);
//request.AddParameter("application/x-www-form-urlencoded; charset=UTF-8", user, ParameterType.RequestBody);
var response = await restClient.ExecutePostTaskAsync(request);
//var response = await restClient.ExecutePostTaskAsync<string>(request); 自动序列化
if (response.StatusCode == System.Net.HttpStatusCode.OK)
{
var result = JsonConvert.DeserializeObject<string>(response.Content);
if (result == "success")
{
return true;
}
return false;
}
else
{
return false;
}
}
public static async System.Threading.Tasks.Task<byte[]> Get(string url)
{
RestClient restClient = Instance(url);
RestRequest request = new RestRequest();
var response = await restClient.ExecuteGetTaskAsync(request);
if (response.StatusCode == System.Net.HttpStatusCode.OK)
{
var bytes = response.RawBytes;
return bytes;
}
return null;
}
}post请求和get请求在编码类型不同，get：仅一种 application/x-www-form-urlencoded，post：application/x-www-form-urlencoded 或 multipart/form-data……等多种编码方式。
restsharp在发送post请求方式时必须设置header的content-type解码方式。
request.AddJsonBody(user);等同于：
request.AddParameter(“application/x-www-form-urlencoded; charset=UTF-8”, user, ParameterType.RequestBody);等同于：
request.RequestFormat =DataFormat.Json;
request.AddBody(user);
这里备注一下以前犯的一个错误，用了AddBody方法必须添加 request.RequestFormat =DataFormat.Json; ，不然会出异常
我们看看下面的AddBody的源码可以知道，除restsharp，.net第三方的网络请求框架还有flurl.http。
/// <summary>
/// Serializes obj to format specified by RequestFormat, but passes xmlNamespace if using the default XmlSerializer
/// The default format is XML. Change RequestFormat if you wish to use a different serialization format.
/// </summary>
/// <param name="obj">The object to serialize</param>
/// <param name="xmlNamespace">The XML namespace to use when serializing</param>
/// <returns>This request</returns>
public IRestRequest AddBody(object obj, string xmlNamespace)
{
string serialized;
string contentType;
// TODO: Make it possible to change the serialiser
switch (RequestFormat)
{
case DataFormat.Json:
serialized = JsonSerializer.Serialize(obj);
contentType = JsonSerializer.ContentType;
break;
case DataFormat.Xml:
XmlSerializer.Namespace = xmlNamespace;
serialized = XmlSerializer.Serialize(obj);
contentType = XmlSerializer.ContentType;
break;
default:
serialized = "";
contentType = "";
break;
}
// passing the content type as the parameter name because there can only be
// one parameter with ParameterType.RequestBody so name isn't used otherwise
// it's a hack, but it works :)
return AddParameter(contentType, serialized, ParameterType.RequestBody);
}
/// <summary>
/// Serializes obj to data format specified by RequestFormat and adds it to the request body.
/// The default format is XML. Change RequestFormat if you wish to use a different serialization format.
/// </summary>
/// <param name="obj">The object to serialize</param>
/// <returns>This request</returns>
public IRestRequest AddBody(object obj)
{
return AddBody(obj, "");
}
/// <summary>
/// Serializes obj to JSON format and adds it to the request body.
/// </summary>
/// <param name="obj">The object to serialize</param>
/// <returns>This request</returns>
public IRestRequest AddJsonBody(object obj)
{
RequestFormat = DataFormat.Json;
return AddBody(obj, "");
}3.HttpClient
性能上不如httpwebrequest，用的非常少，据说使用的时候要注意不少，这里只是写一个简单的例子，不喜勿喷。
需要添加引用System.Http.Http
public class HttpClientUtil
{
public static async System.Threading.Tasks.Task<byte[]> GetBytes(string path)
{
HttpClient client = new HttpClient();
try
{
HttpResponseMessage response = await client.GetAsync(path);
if (response.StatusCode == System.Net.HttpStatusCode.OK)
{
byte[] bytes = await response.Content.ReadAsByteArrayAsync();
return bytes;
}
return null;
}
catch (Exception ex)
{
return null;
}
finally
{
client.Dispose();
}
}
public static async System.Threading.Tasks.Task<bool> PostForm(string path, Dictionary<string,string> _params)
{
var handler = new HttpClientHandler() { AutomaticDecompression = System.Net.DecompressionMethods.GZip };
HttpClient client = new HttpClient();
try
{
client.Timeout = TimeSpan.FromSeconds(5);
//HttpContent httpContent = new StringContent(postData);
//httpContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/x-www-form-urlencoded");
HttpContent httpContent = new FormUrlEncodedContent(_params);
var response = await client.PostAsync(path, httpContent);
if (response.StatusCode == System.Net.HttpStatusCode.OK)
{
string result = await response.Content.ReadAsStringAsync();
result = JsonConvert.DeserializeObject<string>(result);
if (result == "success")
return true;
return false;
}
return false;
}
catch (Exception ex)
{
return false;
}
finally
{
client.Dispose();
}
}
}上面介绍了三种.net方面的网络请求的方法，下面就来说说android方面的网络请求HttpUrlConnection、第三方okhttp。
4.HttpURLConnection
httpURLConnection和HttpWebRequest很相似，是java平台上的一种多用途、轻量级的http客户端，提供的api都非常简单，这一点也是好处，可以使得我们非常方便去拓展他。下面我们简单看下如何使用HttpURLConnection。
引用来自：Java.Net
- HttpURLConnection conn = (HttpURLConnection)url.OpenConnection();创建一个URL对象
- conn.ConnectTimeout = 5000; conn.RequestMethod = “get”;设置请求方式和连接超时的时间
- inputStream = conn.InputStream;获取服务器返回的输入流
- conn.Disconnect();最后调用disconnect方法将http连接关掉
public class HttpUrlConnecUtil
{
/// <summary>
/// get方式获取byte 数组
/// </summary>
/// <param name="path"></param>
/// <returns></returns>
public static byte[] getImage(string path)
{
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection)url.OpenConnection();
conn.ConnectTimeout = 5000;
conn.RequestMethod = "GET";//小写会报错
System.IO.Stream inputStream=null;
try
{
if (conn.ResponseCode == HttpStatus.Ok)
{
inputStream = conn.InputStream;
return StreamUtil.StreamToBytes(inputStream);
}
return null;
}
catch (Exception ex)
{
return null;
}
finally
{
inputStream.Close();
conn.Disconnect();
}
}
public static string post(string path,string name,string pwd)
{
string result = string.Empty;
HttpURLConnection conn = (HttpURLConnection)new URL(path).OpenConnection();
conn.RequestMethod = "POST";
conn.ReadTimeout = 5000;
conn.ConnectTimeout = 5000;
//设置运行输入、输出
conn.DoOutput = true;
conn.DoInput = true;
//post 方式不能缓存，需要手动设置false
conn.UseCaches = false;
string data = "name=" + URLEncoder.Encode(name, "UTF-8") + "&pwd=" + URLEncoder.Encode(pwd,"UTF-8");
Stream outSteam=null;
//获取输出流
try
{
outSteam = conn.OutputStream;
outSteam.Write(Encoding.UTF8.GetBytes(data), 0, data.Length);
outSteam.Flush();
if (conn.ResponseCode == HttpStatus.Ok)
{
Stream input = conn.InputStream;
byte[] bytes = StreamUtil.StreamToBytes(input);
result = bytes.ToString();
}
return result;
}
catch (Exception ex)
{
return "";
}
finally {
outSteam.Close();
conn.Disconnect();
}
}
}
/// <summary>
/// 将流转成byte数组
/// </summary>
/// <param name="stream"></param>
/// <param name="bytes"></param>
public static byte[] StreamToBytes(Stream stream)
{
MemoryStream memoryStream = new MemoryStream();
byte[] buffer = new byte[64 * 1024];
int i;
try
{
while ((i = stream.Read(buffer, 0, buffer.Length)) > 0)
{
memoryStream.Write(buffer, 0, i);
}
var bytes = memoryStream.ToArray();
return bytes;
}
catch (Exception ex)
{
return null;
}
finally {
memoryStream.Close();
stream.Close();
}
}5.OkHttp 最火的android网络请求框架
okhttp是一个第三方的网络请求框架，被广泛适用于android中请求网络数据，是一个一个轻量级的框架，有移动支付Square公司贡献（Picasso和LeakCanary），和HttpURLConnection和api是一致的。在xamarin android中使用的时候需要在nuget中添加引用OkHttp，命名空间：using Square.OkHttp3;
okhttp官网：http://square.github.io/okhttp/
github地址：https://github.com/square/okhttp
除了okhttp外，android中比较流行的网络请求框架还有
retrofit，retrofit2依赖于okhttp；github地址：http://square.github.io/retrofit/，拓展性比较强
volley：google在2013年推出的android异步网络请求框架和图片加载框架
下面看看，如何在xamarin android中使用okhttp发送get，post请求吧。
public class OkHttpClientUtil
{
private OkHttpClient httpClient;
public OkHttpClientUtil()
{
httpClient = new OkHttpClient.Builder()
.ConnectTimeout(5, TimeUnit.Seconds)//连接超时5秒
.WriteTimeout(5, TimeUnit.Seconds)//写入数据超时5秒
.ReadTimeout(5, TimeUnit.Seconds)//读取数据超时5秒
.Build();
}
public static OkHttpClientUtil Instance()
{
return new OkHttpClientUtil();
}
public async System.Threading.Tasks.Task<bool> Post(string url, User user)
{
FormBody.Builder formBody = new FormBody.Builder(); //创建表单请求体
formBody.Add("name", user.Name);
formBody.Add("pwd", user.Pwd);
Request request = new Request.Builder().AddHeader("Content-Type", "application/x-www-form-urlencoded; charset=UTF-8").Url(url).Post(formBody.Build()).Build();
var response = await httpClient.NewCall(request).ExecuteAsync();
if (response.Code() == 200)
{
var result =JsonConvert.DeserializeObject<string>(response.Body().String());
if (result == "success")
{
return true;
}
return false;
}
return false;
}
public async System.Threading.Tasks.Task<byte[]> Get(string url)
{
Request request = new Request.Builder().Url(url).Build();
Response response = await httpClient.NewCall(request).ExecuteAsync();
if (response.Code() == 200)
{
var stream = response.Body().ByteStream();
var bytes = StreamUtil.StreamToBytes(stream);
return bytes;
}
return null;
}
}