UnityWebRequest是新的网络请求Api，分为LLApi和HLApi，其中LLApi为低级api，所谓低级api是指只是提供最基本的api接口，然后需要通过不同的参数来确定请求方式。为此unity提供了高级api（HLApi）即对不同的功能进行了封装，以下基于HLApi做了简单封装。

using System.Collections;
using System;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.Networking;
using System.Collections.Generic;
using System.IO;

public class WebRequestUtility : MonoBehaviour
{
public static WebRequestUtility Instance;

enum RequestType  
{  
    TEXT\_GET,  
    TEXTUREE\_GET,  
    ASSETBUNDEL,  
    POST  
}

public void Get(string url,Action<UnityWebRequest> action)  
{  
    StartCoroutine(Request(url,action,RequestType.TEXT\_GET));  
}

public void GetTexture(string url,Action<UnityWebRequest> action)  
{  
    StartCoroutine(Request(url, action, RequestType.TEXTUREE\_GET));  
}

public void GetAssetBundle(string url,Action<UnityWebRequest> action)  
{  
    StartCoroutine(Request(url, action, RequestType.ASSETBUNDEL));  
}

public void Post(string url, Action<UnityWebRequest> action, List<IMultipartFormSection> formData)  
{  
    StartCoroutine(Request(url, action, RequestType.POST, formData));  
}

IEnumerator Request(string url,Action<UnityWebRequest> action,RequestType type, List<IMultipartFormSection> formData=null)  
{  
    UnityWebRequest webRequest = null;

    switch (type)  
    {  
        case RequestType.TEXT\_GET:  
            webRequest = UnityWebRequest.Get(url);  
            break;  
        case RequestType.TEXTUREE\_GET:  
            webRequest = UnityWebRequestTexture.GetTexture(url);  
            break;  
        case RequestType.ASSETBUNDEL:  
            webRequest = UnityWebRequestAssetBundle.GetAssetBundle(url);  
            break;  
        case RequestType.POST:  
            webRequest = UnityWebRequest.Post(url, formData);  
            break;  
        default:  
            break;  
    }

    if(webRequest==null)  
    {  
        Debug.Log("WebRequest initialise error");  
        yield break;  
    }

    yield return webRequest.SendWebRequest();

    action?.Invoke(webRequest);

    webRequest.Dispose();  
    webRequest = null;  
    Resources.UnloadUnusedAssets();  
}

private void Awake()  
{  
    Instance = this;  
}  

}

调用Get方法

Get(texUrlGet, OnGetAction);

//OnGetAction回调

void OnGetAction(UnityWebRequest webRequest)  
{  
    if(webRequest.isHttpError || webRequest.isNetworkError)  
    {  
        Debug.Log("WebRequest error:"+webRequest.error);  
        return;  
    }

    //下载文本  
    Debug.Log(webRequest.downloadHandler.text);

    //下载图片  
    Texture2D t2d = new Texture2D(, );  
    t2d.LoadImage(webRequest.downloadHandler.data);

    rawImage.texture = t2d;  
}

调用Get方法只获取图片

GetTexture(texUrlGet, OnGetTextueAction);

void OnGetTextueAction(UnityWebRequest webRequest)  
{  
    if (webRequest.isHttpError || webRequest.isNetworkError)  
    {  
        Debug.Log("WebRequest error:" + webRequest.error);  
        return;  
    }

    DownloadHandlerTexture texHandler = (DownloadHandlerTexture)webRequest.downloadHandler;  
    rawImage.texture = ((DownloadHandlerTexture)webRequest.downloadHandler).texture;  
}

post方法

    string headPath = @"D:\\zzh.png";  
    byte\[\] bytes = File.ReadAllBytes(headPath);

    List<IMultipartFormSection> formData = new List<IMultipartFormSection>();  
    formData.Add(new MultipartFormDataSection("api\_key", "\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*"));  
    formData.Add(new MultipartFormDataSection("api\_secret", "\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*"));  
    //formData.Add(new MultipartFormDataSection("image\_url", texUrlGet));  
    formData.Add(new MultipartFormFileSection("image\_file", bytes, "zzh.png", "application/octet-stream"));

    Post("https://api-cn.faceplusplus.com/facepp/v3/detect", OnPostAction, formData);

void OnPostAction(UnityWebRequest webRequest)  
{  
    if (webRequest.isHttpError || webRequest.isNetworkError)  
    {  
        Debug.Log("WebRequest error:" + webRequest.error);  
        return;  
    }

    //下载文本  
    Debug.Log(webRequest.downloadHandler.text);  
}

//---------------------------------2018-1026------------------------------------------//更新

在post请求时根据需求分为四种模式,详细见https://www.cnblogs.com/llstart-new0201/p/6825058.html；所以此次更新增加了post模式，但新加的并未进行测试

using System.Collections;
using System;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.Networking;
using System.Collections.Generic;
using System.IO;

public class WebRequestUtility : MonoBehaviour
{
public RawImage rawImage;

public static WebRequestUtility Instance;

enum RequestType  
{  
    TEXT\_GET,  
    TEXTUREE\_GET,  
    ASSETBUNDEL,  
    POST\_FORM,  
    POST\_URLENCODED,  
    POST\_JSON,  
    POST\_XML  
}

class PostContent  
{  
    public WWWForm formData;  
    public string stringContent;

    public PostContent(WWWForm formData)  
    {  
        this.formData = formData;  
    }

    public PostContent(string text)  
    {  
        this.stringContent = text;  
    }  
}

public void Get(string url,Action<UnityWebRequest> action)  
{  
    StartCoroutine(Request(url,action,RequestType.TEXT\_GET));  
}

public void GetTexture(string url,Action<UnityWebRequest> action)  
{  
    StartCoroutine(Request(url, action, RequestType.TEXTUREE\_GET));  
}

public void GetAssetBundle(string url,Action<UnityWebRequest> action)  
{  
    StartCoroutine(Request(url, action, RequestType.ASSETBUNDEL));  
}

public void Post(string url, Action<UnityWebRequest> action, WWWForm formData)  
{  
    StartCoroutine(Request(url, action, RequestType.POST\_FORM, new PostContent(formData)));  
}

public void PostUrlEncoded(string url,Action<UnityWebRequest> action,string json)  
{  
    StartCoroutine(Request(url, action, RequestType.POST\_URLENCODED,new PostContent(json)));  
}

public void PostJson(string url, Action<UnityWebRequest> action, string json)  
{  
    StartCoroutine(Request(url, action, RequestType.POST\_JSON, new PostContent(json)));  
}

public void PostXml(string url, Action<UnityWebRequest> action, string json)  
{  
    StartCoroutine(Request(url, action, RequestType.POST\_XML, new PostContent(json)));  
}

IEnumerator Request(string url,Action<UnityWebRequest> action,RequestType type, PostContent postContent =null)  
{  
    UnityWebRequest webRequest = null;

    switch (type)  
    {  
        case RequestType.TEXT\_GET:  
            webRequest = UnityWebRequest.Get(url);  
            break;  
        case RequestType.TEXTUREE\_GET:  
            webRequest = UnityWebRequestTexture.GetTexture(url);  
            break;  
        case RequestType.ASSETBUNDEL:  
            webRequest = UnityWebRequestAssetBundle.GetAssetBundle(url);  
            break;  
        case RequestType.POST\_FORM:  
            webRequest = UnityWebRequest.Post(url, postContent.formData);  
            break;  
        case RequestType.POST\_URLENCODED:  
            webRequest = UnityWebRequest.Post(url, postContent.stringContent);  
            //可以不进行设置，此时默认为urlencoded  
            webRequest.SetRequestHeader("Content-Type", "application/x-www-form-urlencoded");  
            break;  
        case RequestType.POST\_JSON:  
            webRequest = UnityWebRequest.Post(url, postContent.stringContent);  
            webRequest.SetRequestHeader("Content-Type", "application/json");  
            break;  
        case RequestType.POST\_XML:  
            webRequest = UnityWebRequest.Post(url, postContent.stringContent);  
            webRequest.SetRequestHeader("Content-Type", "text/xml");//注:text/plain为纯文本  
            break;  
        default:  
            break;  
    }

    if(webRequest==null)  
    {  
        Debug.Log("WebRequest initialise error");  
        yield break;  
    }

    yield return webRequest.SendWebRequest();

    action?.Invoke(webRequest);

    action = null;  
    webRequest.Dispose();  
    webRequest = null;  
    Resources.UnloadUnusedAssets();  
}

private void Awake()  
{  
    Instance = this;  
}  

}

鉴于post请求可能存在的问题，如https://www.jianshu.com/p/0f1f24829db3所述，做如下代码，

//通过PUT方式构造HTTP请求
byte[] myData = System.Text.Encoding.UTF8.GetBytes("This is some test data");
UnityWebRequest www = UnityWebRequest.Put("http://www.my-server.com/upload", myData);

//构造好后，手动将请求方式更改为POST

www.method = UnityWebRequest.kHttpVerbPOST;

//常规的发送，接收操作

yield return www.Send();  
if(www.isError) {  
  Debug.Log(www.error);  
}  
else {  
  Debug.Log("Upload complete!");  
}

unityWebRequest  LLAPI

public IEnumerator PostUrl(string url, string postData)
{
using (UnityWebRequest www = new UnityWebRequest(url,"POST"))
{
byte[] postBytes = System.Text.Encoding.UTF8.GetBytes(postData);
www.uploadHandler = (UploadHandler)new UploadHandlerRaw(postBytes);
www.downloadHandler = (DownloadHandler)new DownloadHandlerBuffer();
www.SetRequestHeader("Content-Type", "application/json");
yield return www.Send();
if (www.isError)
{
Debug.Log(www.error);
}
else
{
// Show results as text
if (www.responseCode == )
{
Debug.Log(www.downloadHandler.text);
}
}
}
}