vb.net写的windows应用程序如何调用webapi?

这个函数能帮到你

 Public Shared Function GetData(ByVal url As String, ByVal data As String) As String  
            Dim request As HttpWebRequest = WebRequest.Create(url + "?" + data)  
            request.Method = "GET"  
            Dim sr As StreamReader = New StreamReader(request.GetResponse().GetResponseStream)  
            Return sr.ReadToEnd  
    End Function 

WEB API 其实就是访问一个网页地址，参数一般通过URL方式提交，返回值根据该API的约定，或为JOSN或为XML，无非也就是一个字符串，解析一下就可以了。

楼主现在是卡在不会访问网页还是不会组织URL，或者是解析返回值？

MULTI/FORM-DATA相当于上传文件了。
参考下面的代码：

Imports System  
Imports System.Collections.Generic  
Imports System.Text  
Imports System.Net  
Imports System.IO  
Namespace SimpleWebRequest
Class Program  
static void Main(string() args)  
{  
Console.WriteLine( 
PostDataToUrl("test", "http://www.microsoft.com")  
)  
}  
'/<summary>  
'/ Post data到url  
'/</summary>  
'/<param name="data">要post的数据</param>  
'/<param name="url">目标url</param>  
'/<returns>服务器响应</returns>  
static String PostDataToUrl(String data, String url)  
{  
Dim encoding As Encoding =  Encoding.GetEncoding(sRequestEncoding) 
Dim bytesToPost() As Byte =  encoding.GetBytes(data) 
Return PostDataToUrl(bytesToPost,url)
}  
'/<summary>  
'/ Post data到url  
'/</summary>  
'/<param name="data">要post的数据</param>  
'/<param name="url">目标url</param>  
'/<returns>服务器响应</returns>  
static String PostDataToUrl(byte() data, String url)  
{  
#region 创建httpWebRequest对象  
Dim webRequest As WebRequest =  WebRequest.Create(url) 
Dim httpRequest As HttpWebRequest =  webRequest as HttpWebRequest 'as用于类型转换  
If httpRequest Is Nothing Then
Throw New ApplicationException( 
String.Format("Invalid url string: {0}", url)  
)
End If
#End Region  
#region 填充httpWebRequest的基本信息  
httpRequest.UserAgent = sUserAgent  
httpRequest.ContentType = sContentType  
httpRequest.Method = "POST"  
#End Region  
#region 填充要post的内容  
httpRequest.ContentLength = data.Length  
Dim requestStream As Stream =  httpRequest.GetRequestStream() 
requestStream.Write(data, 0, data.Length)  
requestStream.Close()  
#End Region  
#region 发送post请求到服务器并读取服务器返回信息  
Dim responseStream As Stream
Try
responseStream = httpRequest.GetResponse().GetResponseStream()
Catch e As Exception
' log error  
Console.WriteLine( 
String.Format("POST操作发生异常：{0}", e.Message)  
)  
Throw e
End Try
#End Region  
#region 读取服务器返回信息  
Dim stringResponse As String =  String.Empty 
using(StreamReader responseReader =  
New StreamReader(responseStream, Encoding.GetEncoding(sResponseEncoding)))  
{  
stringResponse = responseReader.ReadToEnd()  
}  
responseStream.Close()  
#End Region  
Return stringResponse
End Namespace
{  
Class Program  
static void Main(string() args)  
{  
Console.WriteLine( 
PostDataToUrl("test", "http://www.microsoft.com")  
)  
}  
'/<summary>  
'/ Post data到url  
'/</summary>  
'/<param name="data">要post的数据</param>  
'/<param name="url">目标url</param>  
'/<returns>服务器响应</returns>  
static String PostDataToUrl(String data, String url)  
{  
Dim encoding As Encoding =  Encoding.GetEncoding(sRequestEncoding) 
Dim bytesToPost() As Byte =  encoding.GetBytes(data) 
Return PostDataToUrl(bytesToPost,url)
}  
'/<summary>  
'/ Post data到url  
'/</summary>  
'/<param name="data">要post的数据</param>  
'/<param name="url">目标url</param>  
'/<returns>服务器响应</returns>  
static String PostDataToUrl(byte() data, String url)  
{  
#region 创建httpWebRequest对象  
Dim webRequest As WebRequest =  WebRequest.Create(url) 
Dim httpRequest As HttpWebRequest =  webRequest as HttpWebRequest 'as用于类型转换  
If httpRequest Is Nothing Then
Throw New ApplicationException( 
String.Format("Invalid url string: {0}", url)  
)
End If
#End Region  
#region 填充httpWebRequest的基本信息  
httpRequest.UserAgent = sUserAgent  
httpRequest.ContentType = sContentType  
httpRequest.Method = "POST"  
#End Region  
#region 填充要post的内容  
httpRequest.ContentLength = data.Length  
Dim requestStream As Stream =  httpRequest.GetRequestStream() 
requestStream.Write(data, 0, data.Length)  
requestStream.Close()  
#End Region  
#region 发送post请求到服务器并读取服务器返回信息  
Dim responseStream As Stream
Try
responseStream = httpRequest.GetResponse().GetResponseStream()
Catch e As Exception
' log error  
Console.WriteLine( 
String.Format("POST操作发生异常：{0}", e.Message)  
)  
Throw e
End Try
#End Region  
#region 读取服务器返回信息  
Dim stringResponse As String =  String.Empty 
using(StreamReader responseReader =  
New StreamReader(responseStream, Encoding.GetEncoding(sResponseEncoding)))  
{  
stringResponse = responseReader.ReadToEnd()  
}  
responseStream.Close()  
#End Region  
Return stringResponse
}  
const String sUserAgent =  
"Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.2; .NET CLR 1.1.4322; .NET CLR 2.0.50727)"  
const String sContentType =  
"application/x-www-form-urlencoded"  
const String sRequestEncoding = "ascii"  
const String sResponseEncoding = "gb2312"
End Class

@kafly
非常感谢您的回复。问题的关键应该在如何组织URL访问网页

对方给出的信息是这样的：
接口地址：http://192.168.1.1/webapi (例)
参数：paramters

上传图片接口
使用POST multipart/form-data形式上传，字段如下：
字段名 类型
project_id 字符串

enterprise__uscc_ 字符串

detecting_uscc 字符串

image_id 字符串
image_file 文件 图片文件内容

我需要用vb.net 写一段代码，上传字串和文件内容

http://www.cnblogs.com/developersupport/p/aspnet-webapi.html
看看这篇文章，希望能帮助你