【UE4 C++】 解析与构建 Json 数据

准备条件

Json 格式

{
"Players":[
		{
			"Name": "Player1",
			"health": 200,
			"icon": "Texture2D'/Game/FourEvilDragonsHP/Textures/DragonTheUsurper/BlueHPTex.BlueHPTex'"
		},
		{
			"Name": "Player2",
			"health": 90,
			"icon": "Texture2D'/Game/FourEvilDragonsHP/Textures/DragonTheSoulEater/BlueHPTex.BlueHPTex'"
		},
		{
			"Name": "Player3",
			"health": 150,
			"icon": "None"
		}
	]
}

UE4 添加Json模块

Build.cs中将Json模块导入

PublicDependencyModuleNames.AddRange(new string[] { "Core", "CoreUObject", "Engine", "InputCore", "UMG", "Json" });

数据说明

FJsonObject

• 表示一个Json对象，可以作为值 嵌套

• 读取数据相关节点

  TSharedPtr<FJsonValue> TryGetField( const FString& FieldName )
  
  bool HasField( const FString& FieldName)
  
  double GetNumberField(const FString& FieldName)
  int32 GetIntegerField(const FString& FieldName)
  
  bool TryGetNumberField(const FString& FieldName, double& OutNumber)
  bool TryGetNumberField(const FString& FieldName, int32& OutNumber)
  bool TryGetNumberField(const FString& FieldName, uint32& OutNumber)
  bool TryGetNumberField(const FString& FieldName, int64& OutNumber)
  
  FString GetStringField(const FString& FieldName)
  bool TryGetStringField(const FString& FieldName, FString& OutString)
  bool TryGetStringArrayField(const FString& FieldName, TArray<FString>& OutArray)
  
  bool TryGetEnumArrayField(const FString& FieldName, TArray<TEnum>& OutArray)
  
  bool GetBoolField(const FString& FieldName)
  bool TryGetBoolField(const FString& FieldName, bool& OutBool)
  
  const TArray< TSharedPtr<FJsonValue> >& GetArrayField(const FString& FieldName)
  bool TryGetArrayField(const FString& FieldName, const TArray< TSharedPtr<FJsonValue> >*& OutArray)
  
  const TSharedPtr<FJsonObject>& GetObjectField(const FString& FieldName)
  bool TryGetObjectField(const FString& FieldName, const TSharedPtr<FJsonObject>*& OutObject)
  

• 存储数据的节点

  void SetField( const FString& FieldName, const TSharedPtr<FJsonValue>& Value )
  
  void RemoveField(const FString& FieldName);
  
  void SetNumberField( const FString& FieldName, double Number )
  
  void SetStringField( const FString& FieldName, const FString& StringValue )
  
  void SetBoolField( const FString& FieldName, bool InValue )
  
  void SetArrayField( const FString& FieldName, const TArray< TSharedPtr<FJsonValue> >& Array )
  
  void SetObjectField( const FString& FieldName, const TSharedPtr<FJsonObject>& JsonObject )
  

FJsonValue

读取 Json 数据

本地读取

• 注意 JsonReader 的类型 TSharedRef<TJsonReader<>>，使用 TJsonReaderFactory<>::Create 创建

• 使用 FJsonSerializer::Deserialize 将 Json String 转成 JsonObject

• FJsonValue 可以再度转化城成FJsonObject，或者直接提取 基本类型数据

  FString JsonPath = FPaths::ProjectDir() + TEXT("DataDrive/UserInfo.json");
  	JsonPath = FPaths::ConvertRelativePathToFull(JsonPath);
  	if (FPlatformFileManager::Get().GetPlatformFile().FileExists(*JsonPath))
  	{
  		UKismetSystemLibrary::PrintString(GetWorld(), *JsonPath);
  		FString JsonData;
  		FFileHelper::LoadFileToString(JsonData, *JsonPath);
  
  		// FString 转 JsonObj
  		TSharedRef<TJsonReader<>> JsonReader = TJsonReaderFactory<>::Create(JsonData);
  		TSharedPtr<FJsonObject> RootJsonObj = MakeShareable(new FJsonObject);
  		if (FJsonSerializer::Deserialize(JsonReader, RootJsonObj))
  		{
  			UE_LOG(LogTemp, Warning, TEXT("JsonData:%s"), *JsonData );
  			const TArray< TSharedPtr<FJsonValue> >* members;
  			if (RootJsonObj->TryGetArrayField(TEXT("Players"),members))
  			{
  				for (TSharedPtr<FJsonValue> item: * members)
  				{
  					TSharedPtr<FJsonObject>itemObjet = item->AsObject();
  					UE_LOG(LogTemp, Warning, TEXT("name:%s health:%d"), *itemObjet->GetStringField(TEXT("Name")),itemObjet->GetIntegerField(TEXT("health")) );
  				}
  			}
  		}
  		else
  			UKismetSystemLibrary::PrintString(GetWorld(), TEXT("FJsonSerializer::Deserialize Failed!"));
  	}
  

  

  网络读取 Json

  • 与本地类似，但是通过 URL 获取 Json 数据
  • 可以使用 VaRest 插件，支持读写

写入 Json 数据

基本类型构造 Json 数据

• 注意 Write 类型为 TSharedRef<TJsonWriter<>>，使用 TJsonWriterFactory<>::Create() 创建

• 步骤

  • WriteObjectStart
  • WriteValue 普通字段
  • 数组字段
    • WriteArrayStart
    • WriteObjectStart
    • WriteValue (可以多个字段)
    • WriteObjectEnd
    • WriteArrayEnd
  • WriteObjectEnd
  • Close();

• 代码实现

  struct Info {
  	FString name;
  	int32 health;
  };
  
  FString InfoCategory = "Player State";
  TArray<Info> Players;
  struct Info info;
  
  info.name = TEXT("城主");	info.health = 30;	Players.Add(info);
  
  info.name = TEXT("白月魁");	info.health = 200;	Players.Add(info);
  
  info.name = TEXT("临渊者");	info.health = 999;	Players.Add(info);
  
  FString OutJsonData;
  TSharedRef<TJsonWriter<>> Writer = TJsonWriterFactory<>::Create(&OutJsonData);
  //TSharedRef<TJsonWriter<TCHAR, TCondensedJsonPrintPolicy<TCHAR>>> Writer = TJsonWriterFactory< TCHAR, TCondensedJsonPrintPolicy<TCHAR> >::Create(&OutJsonData);
  
  Writer->WriteObjectStart();						// JSON对象开始
  Writer->WriteValue(L"category", InfoCategory);  // 填充普通字段
  
  Writer->WriteArrayStart(L"players");			// Json 数组字段开始
  for (Info player : Players)
  {
  	Writer->WriteObjectStart();
  	Writer->WriteValue(L"name", player.name);		// 填充普通字段
  	Writer->WriteValue(L"health", player.health);	// 填充普通字段
  	Writer->WriteObjectEnd();
  }
  Writer->WriteArrayEnd();               // Json 数组字段结束
  Writer->WriteObjectEnd();              //JSON对象结束
  Writer->Close();
  
  UE_LOG(LogTemp, Warning, TEXT("JsonData:%s"), *OutJsonData );
  

  

FJsonObject 构造 Json 数据

• 主要 FJsonObject 转 JsonValue

• FJsonSerializer::Serialize 将 FJsonObject 转 FString

  TSharedPtr<FJsonObject> JsonObject = MakeShareable(new FJsonObject);
  TArray<TSharedPtr<FJsonValue>> PlayersData;
  
  TSharedPtr<FJsonObject> Player1 = MakeShareable(new FJsonObject);
  Player1->SetStringField(TEXT("name"), TEXT("城主"));
  Player1->SetNumberField(TEXT("health"), 30);
  Player1->SetStringField(TEXT("icon"), TEXT(""));
  PlayersData.Add(MakeShareable(new FJsonValueObject(Player1)));
  
  TSharedPtr<FJsonObject> Player2 = MakeShareable(new FJsonObject);
  Player2->SetStringField(TEXT("name"), TEXT("白月魁"));
  Player2->SetNumberField(TEXT("health"), 200);
  Player2->SetStringField(TEXT("icon"), TEXT(""));
  PlayersData.Add(MakeShareable(new FJsonValueObject(Player2)));
  
  TSharedPtr<FJsonObject> Player3 = MakeShareable(new FJsonObject);
  Player3->SetStringField(TEXT("name"), TEXT("临渊者"));
  Player3->SetNumberField(TEXT("health"), 999);
  Player3->SetStringField(TEXT("icon"), TEXT(""));
  PlayersData.Add(MakeShareable(new FJsonValueObject(Player3)));
  
  JsonObject->SetArrayField(TEXT("players"), PlayersData);
  
  FString OutJsonData;
  TSharedRef<TJsonWriter<>> Writer = TJsonWriterFactory<>::Create(&OutJsonData);
  FJsonSerializer::Serialize(JsonObject.ToSharedRef(), Writer);
  
  UE_LOG(LogTemp, Warning, TEXT("JsonData:%s"), *OutJsonData );
  

参考

• FJsonObject