准备条件

{
"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"
        }
    ]
}

Build.cs中将Json模块导入

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

数据说明

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 )

读取 Json 数据

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&lt;TJsonReader&lt;&gt;&gt; JsonReader = TJsonReaderFactory&lt;&gt;::Create(JsonData);
    TSharedPtr&lt;FJsonObject&gt; RootJsonObj = MakeShareable(new FJsonObject);
    if (FJsonSerializer::Deserialize(JsonReader, RootJsonObj))
    {
        UE_LOG(LogTemp, Warning, TEXT("JsonData:%s"), *JsonData );
        const TArray&lt; TSharedPtr&lt;FJsonValue&gt; &gt;* members;
        if (RootJsonObj-&gt;TryGetArrayField(TEXT("Players"),members))
        {
            for (TSharedPtr&lt;FJsonValue&gt; item: * members)
            {
                TSharedPtr&lt;FJsonObject&gt;itemObjet = item-&gt;AsObject();
                UE_LOG(LogTemp, Warning, TEXT("name:%s health:%d"), *itemObjet-&gt;GetStringField(TEXT("Name")),itemObjet-&gt;GetIntegerField(TEXT("health")) );
            }
        }
    }
    else
        UKismetSystemLibrary::PrintString(GetWorld(), TEXT("FJsonSerializer::Deserialize Failed!"));
}</code></pre>


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

注意 Write 类型为 TSharedRef>，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 );

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

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准备条件

数据说明

读取 Json 数据

写入 Json 数据

参考

【UE4 C++】解析与构建 Json 数据