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

原文链接: https://www.cnblogs.com/shiroe/p/14751769.html

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【UE4 C++】 解析与构建 Json 数据