View source for UE4与WEB服务器交互(json)

[[Category:Tutorials]] 
[[Category:Code]]
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== 概述 ==
制作游戏在很多情况下需要和WEB服务器进行交互，最常见的是在做Demo时需要通过游戏向WEB服务器传递数据（登录/注册验请求），WEB服务器处理（操作数据库）之后返回结果并调用指定的方法。
该教程简单介绍了如何通过UE4向WEB服务器（PHP）发送json数据包及回调方法。


== 添加模块和头文件引用 ==
在代码编辑器中打开项目解决方案，在<Solution Name>/Source/<ProjectName>路径下，找到并打开<ProjectName>.Build.cs文件，添加HTTP模块：
<syntaxhighlight lang="cpp"> 
PrivateDependencyModuleNames.AddRange(new string[] {"HTTP"}); 
PrivateIncludePathModuleNames.AddRange(new string[] {"HTTP"});
</syntaxhighlight>
然后在需要实现该功能的类文件中添加如下的头文件引用:
<syntaxhighlight lang="cpp"> 
#include "Http.h"
#include "Json.h"
</syntaxhighlight>


== 创建json数据包 ==
数据内容为：
 { "user" : "StormUnited"}

创建：
<syntaxhighlight lang="cpp"> 
// Create a writer and hold it in this FString
FString JsonStr;
TSharedRef< TJsonWriter<TCHAR, TCondensedJsonPrintPolicy<TCHAR> > > JsonWriter = TJsonWriterFactory<TCHAR, TCondensedJsonPrintPolicy<TCHAR> >::Create(&JsonStr);
JsonWriter->WriteObjectStart();
JsonWriter->WriteValue(TEXT("user"), TEXT("StormUnited"));
JsonWriter->WriteObjectEnd();

// Close the writer and finalize the output such that JsonStr has what we want
JsonWriter->Close();
</syntaxhighlight>

至此，json数据包准备完成。


== 准备接收json数据包的PHP网页 ==
本示例中使用了PHP，你可以选择使用搭建动态网站或者服务器的开源软件，比如说wamp/lamp等在本机上建立一个WEB服务器来解析PHP页面。
创建mywebpage.php文件，并添加如下代码：
<syntaxhighlight lang="php">
<?php
     // 首先接收上传的数据
     $post_data = file_get_contents('php://input');
     // 解析json字符串
     $obj = json_decode($post_data);
     // 获取包含在Json字符串中的数据
     echo $obj->{'user'};
?>
</syntaxhighlight>


== POST数据 ==
将通过如下的代码将上面准备好的json数据包提交给 http://localhost/mywebpage.php

* SetHeader：可以设置POST数据的格式
* SetURL：可以指定用于处理上传数据的链接
* SetVerb：可以设置POST/PUT/GET
* SetContentAsString：用于填充上传的数据内容
* OnProcessRequestComplete().BindUObject 用于指定在发送请求之后的回调方法。

<syntaxhighlight lang="cpp">
TSharedRef<IHttpRequest> HttpRequest = FHttpModule::Get().CreateRequest();
HttpRequest->SetHeader(TEXT("Content-Type"), TEXT("application/json; charset=utf-8"));
HttpRequest->SetURL(TEXT("http://localhost/mywebpage.php"));
HttpRequest->SetVerb(TEXT("POST"));
HttpRequest->SetContentAsString(JsonStr);
HttpRequest->OnProcessRequestComplete().BindUObject(this, &ASUMiniGameMode::HttpCompleteCallback);
HttpRequest->ProcessRequest();
</syntaxhighlight>  


关于回调函数的结构：void HttpCompleteCallback(FHttpRequestPtr Request, FHttpResponsePtr Response, bool bWasSuccessful);
示例：
<syntaxhighlight lang="cpp">
void ASUMiniGameMode::HttpCompleteCallback(FHttpRequestPtr Request, FHttpResponsePtr Response, bool bWasSuccessful)
{
     FString MessageBody = "";

     // If HTTP fails client-side, this will still be called but with a NULL shared pointer!
     if (!Response.IsValid())
     {
          MessageBody = "{\"success\":\"Error: Unable to process HTTP Request!\"}";
     }
     else if (EHttpResponseCodes::IsOk(Response->GetResponseCode()))
     {
          MessageBody = Response->GetContentAsString();
     }
     else
     {
          MessageBody = FString::Printf(TEXT("{\"success\":\"HTTP Error: %d\"}"), Response->GetResponseCode());
     }
}
</syntaxhighlight>

一旦发送出请求后肯定会调用HttpCompleteCallback方法，WEB服务器处理的数据结果包含在Response参数中，可以通过Response->GetContentAsString()来获取返回的字符串，比如在本例中是StormUnited。

== 总结 ==
联系我：[[User:hexcola|hexcola]]

== 常见问题及参考 ==
* https://answers.unrealengine.com/questions/4383/sending-an-fstring-via-sockets.html
* https://answers.unrealengine.com/questions/4406/need-help-with-json-objects.html
* https://answers.unrealengine.com/questions/2830/best-way-to-perform-a-http-request.html
* https://answers.unrealengine.com/questions/3530/does-httprequest-use-httpmanager-by-default.html
* https://answers.unrealengine.com/questions/2830/best-way-to-perform-a-http-request.html
* https://answers.unrealengine.com/questions/23170/making-http-calls.html
* https://answers.unrealengine.com/questions/31079/http%E9%80%9A%E4%BF%A1%E3%81%AB%E3%81%A4%E3%81%84%E3%81%A6.html
* https://answers.unrealengine.com/questions/26704/trouble-deserializing-json.html
* https://answers.unrealengine.com/questions/2830/best-way-to-perform-a-http-request.html