UE4 蓝图Structure与Json的读写

蓝图创建Structure

测试读JSON：

测试写JSON

结果：

因为代码比较长，所以先解释一下，最后在放完整代码。

代码解析：

一、把蓝图Structure暴露到C++

UFUNCTION(BlueprintCallable, Category = "Json", CustomThunk, meta = (CustomStructureParam = "AnyStruct"))
static bool ReadJson(const FString& JsonStr, UStructProperty* AnyStruct);

DECLARE_FUNCTION(execReadJson) {
       P_GET_PROPERTY(UStrProperty, JsonStr);
       Stack.Step(Stack.Object, NULL);
       UStructProperty* StructProperty = ExactCast<UStructProperty>(Stack.MostRecentProperty);
       void* StructPtr = Stack.MostRecentPropertyAddress;
       P_FINISH;

*(bool*)RESULT_PARAM = JsonStrToStruct(StructProperty, StructPtr, JsonStr);

}

官方文档的说明：

CustomThunk

UnrealHeaderTool 代码生成器将不为此函数生成thunk，用户需要提供一个thunk。

CustomStructureParam="Parameter1, Parameter2, ..")

列出的参数都会被视为通配符。此说明符需要 UFUNCTION-level specifier、CustomThunk，而它们又需要用户提供自定义的 exec 函数。在此函数中，可对参数类型进行检查，可基于这些参数类型执行合适的函数调用。永不应调用基础 UFUNCTION，出现错误时应进行断言或记录。

要声明自定义 exec 函数，使用语法 DECLARE_FUNCTION(execMyFunctionName)，MyFunctionName 为原函数命名。

这样，我们就能在自己C++代码里解析蓝图的结构体了。

二、UStruct与JSON的转换

JsonUtilities模块的FJsonObjectConverter类里有接口进行UStruct到Json的互相转换，但是只能是C++类，不能是蓝图结构体。原因其实很简单。

下面这个是FJsonObjectConverter类的JsonAttributesToUStructWithContainer函数：

bool JsonAttributesToUStructWithContainer(const TMap< FString, TSharedPtr<FJsonValue> >& JsonAttributes, const UStruct* StructDefinition, void* OutStruct, const UStruct* ContainerStruct, void* Container, int64 CheckFlags, int64 SkipFlags)
   {
       if (StructDefinition == FJsonObjectWrapper::StaticStruct())
       {
           // Just copy it into the object
           FJsonObjectWrapper* ProxyObject = (FJsonObjectWrapper *)OutStruct;
           ProxyObject->JsonObject = MakeShared<FJsonObject>();
           ProxyObject->JsonObject->Values = JsonAttributes;
           return true;
       }

int32 NumUnclaimedProperties = JsonAttributes.Num();
       if (NumUnclaimedProperties <= 0)
       {
           return true;
       }

// iterate over the struct properties
       for (TFieldIterator<UProperty> PropIt(StructDefinition); PropIt; ++PropIt)
       {
           UProperty* Property = *PropIt;

// Check to see if we should ignore this property
           if (CheckFlags != 0 && !Property->HasAnyPropertyFlags(CheckFlags))
           {
               continue;
           }
           if (Property->HasAnyPropertyFlags(SkipFlags))
           {
               continue;
           }

// find a json value matching this property name
           const TSharedPtr<FJsonValue>* JsonValue = JsonAttributes.Find(Property->GetName());
           if (!JsonValue)
           {
               // we allow values to not be found since this mirrors the typical UObject mantra that all the fields are optional when deserializing
               continue;
           }

if (JsonValue->IsValid() && !(*JsonValue)->IsNull())
           {
               void* Value = Property->ContainerPtrToValuePtr<uint8>(OutStruct);
               if (!JsonValueToUPropertyWithContainer(*JsonValue, Property, Value, ContainerStruct, Container, CheckFlags, SkipFlags))
               {
                   UE_LOG(LogJson, Error, TEXT("JsonObjectToUStruct - Unable to parse %s.%s from JSON"), *StructDefinition->GetName(), *Property->GetName());
                   return false;
               }
           }

if (--NumUnclaimedProperties <= 0)
           {
               // If we found all properties that were in the JsonAttributes map, there is no reason to keep looking for more.
               break;
           }
       }

return true;
}

当传入的是蓝图的结构体时，Property->GetName()这个其实是返回变量名加后缀的，也就是因为多了后缀JsonAttributes.Find找不到同名的参数，所以把改成去掉后缀的名字就能够找到。在源码里把这些改了就会发现可以读到了。

不过我懒得改源码。所以把相关的都复制黏贴到自己的类里修改后直接调用自己类里的。

所以其实主要功能就是复制FJsonObjectConverter里改的，而且就是把Property->GetName()的地方改下而已。

即以下函数

JsonAttributesToUStructWithContainer

UStructToJsonAttributes

JsonValueToUPropertyWithContainer

ConvertScalarJsonValueToUPropertyWithContainer

UPropertyToJsonValue

ConvertScalarUPropertyToJsonValue

C++代码

头文件：

#pragma once#include "CoreMinimal.h"
#include "Kismet/BlueprintFunctionLibrary.h"
#include "JsonOperateLibrary.generated.h"class FJsonValue;/*** */
UCLASS()
class MY_API UJsonOperateLibrary :public UBlueprintFunctionLibrary
{GENERATED_BODY()public:UFUNCTION(BlueprintCallable, Category = "Json", CustomThunk, meta = (CustomStructureParam = "AnyStruct"))static bool ReadJson(const FString& JsonStr, UStructProperty* AnyStruct);DECLARE_FUNCTION(execReadJson) {P_GET_PROPERTY(UStrProperty, JsonStr);Stack.Step(Stack.Object, NULL);UStructProperty* StructProperty = ExactCast<UStructProperty>(Stack.MostRecentProperty);void* StructPtr = Stack.MostRecentPropertyAddress;P_FINISH;*(bool*)RESULT_PARAM = JsonStrToStruct(StructProperty, StructPtr, JsonStr);}UFUNCTION(BlueprintCallable, Category = "Json", CustomThunk, meta = (CustomStructureParam = "AnyStruct"))static bool WriteJson( UStructProperty* AnyStruct,FString& JsonStr);DECLARE_FUNCTION(execWriteJson) {Stack.Step(Stack.Object, NULL);UStructProperty* StructProperty = ExactCast<UStructProperty>(Stack.MostRecentProperty);void* StructPtr = Stack.MostRecentPropertyAddress;P_GET_PROPERTY_REF(UStrProperty, JsonStr);P_FINISH;*(bool*)RESULT_PARAM = StructToJsonStr(StructProperty, StructPtr,JsonStr);}static bool JsonStrToStruct(UStructProperty* StructProperty, void* StructPtr, const FString& InString);static bool StructToJsonStr(UStructProperty* StructProperty, void* StructPtr, FString& InString);private:static FString GetShortName(UProperty* Property);static bool JsonAttributesToUStructWithContainer(const TMap< FString, TSharedPtr<FJsonValue> >& JsonAttributes, const UStruct* StructDefinition, void* OutStruct, const UStruct* ContainerStruct, void* Container, int64 CheckFlags, int64 SkipFlags);static bool UStructToJsonAttributes(const UStruct* StructDefinition, const void* Struct, TMap< FString, TSharedPtr<FJsonValue> >& OutJsonAttributes, int64 CheckFlags, int64 SkipFlags);static bool JsonValueToUPropertyWithContainer(const TSharedPtr<FJsonValue>& JsonValue, UProperty* Property, void* OutValue, const UStruct* ContainerStruct, void* Container, int64 CheckFlags, int64 SkipFlags);static bool ConvertScalarJsonValueToUPropertyWithContainer(const TSharedPtr<FJsonValue>& JsonValue, UProperty* Property, void* OutValue, const UStruct* ContainerStruct, void* Container, int64 CheckFlags, int64 SkipFlags);static TSharedPtr<FJsonValue> UPropertyToJsonValue(UProperty* Property, const void* Value, int64 CheckFlags, int64 SkipFlags);static TSharedPtr<FJsonValue> ConvertScalarUPropertyToJsonValue(UProperty* Property, const void* Value, int64 CheckFlags, int64 SkipFlags);
};

cpp文件：

// Fill out your copyright notice in the Description page of Project Settings.#include "JsonOperateLibrary.h"
#include "Json.h"
#include "JsonUtilities.h"
#include "UObject/EnumProperty.h"
#include "UObject/TextProperty.h"
#include "UObject/Package.h"
#include "UObject/ObjectMacros.h"
#include "JsonObjectConverter.h"bool UJsonOperateLibrary::JsonStrToStruct(UStructProperty* StructProperty, void* StructPtr, const FString& InString)
{UScriptStruct* Struct = StructProperty->Struct;TSharedPtr<FJsonObject> JsonObject;TSharedRef<TJsonReader<> > JsonReader = TJsonReaderFactory<>::Create(InString);if (FJsonSerializer::Deserialize(JsonReader, JsonObject) || !JsonObject.IsValid()){return JsonAttributesToUStructWithContainer(JsonObject->Values, Struct, StructPtr, Struct, StructPtr, 1, 0);}return false;
}bool UJsonOperateLibrary::StructToJsonStr(UStructProperty* StructProperty, void* StructPtr, FString& InString)
{UScriptStruct* Struct = StructProperty->Struct;TSharedRef<FJsonObject> JsonObject = MakeShared<FJsonObject>();if (UStructToJsonAttributes(Struct, StructPtr, JsonObject->Values, 1, 0)){bool bSuccess = false;TSharedRef<TJsonWriter<TCHAR, TPrettyJsonPrintPolicy<TCHAR>> > JsonWriter = TJsonWriterFactory<TCHAR, TPrettyJsonPrintPolicy<TCHAR>>::Create(&InString, 0);bSuccess = FJsonSerializer::Serialize(JsonObject, JsonWriter);JsonWriter->Close();if (bSuccess){return true;}else{UE_LOG(LogJson, Warning, TEXT("UStructToJsonObjectString - Unable to write out json"));}}return false;}FString UJsonOperateLibrary::GetShortName(UProperty* Property)
{FString PropertyName = Property->GetName();FString Left;FString Right;if (PropertyName.Split("_", &Left, &Right)){return Left;}return PropertyName;
}bool UJsonOperateLibrary::JsonAttributesToUStructWithContainer(const TMap< FString, TSharedPtr<FJsonValue> >& JsonAttributes, const UStruct* StructDefinition, void* OutStruct, const UStruct* ContainerStruct, void* Container, int64 CheckFlags, int64 SkipFlags)
{if (StructDefinition == FJsonObjectWrapper::StaticStruct()){// Just copy it into the objectFJsonObjectWrapper* ProxyObject = (FJsonObjectWrapper*)OutStruct;ProxyObject->JsonObject = MakeShared<FJsonObject>();ProxyObject->JsonObject->Values = JsonAttributes;return true;}int32 NumUnclaimedProperties = JsonAttributes.Num();if (NumUnclaimedProperties <= 0){return true;}// iterate over the struct propertiesfor (TFieldIterator<UProperty> PropIt(StructDefinition); PropIt; ++PropIt){UProperty* Property = *PropIt;// Check to see if we should ignore this propertyif (CheckFlags != 0 && !Property->HasAnyPropertyFlags(CheckFlags)){continue;}if (Property->HasAnyPropertyFlags(SkipFlags)){continue;}// find a json value matching this property nameconst TSharedPtr<FJsonValue>* JsonValue = JsonAttributes.Find(GetShortName(Property));if (!JsonValue){// we allow values to not be found since this mirrors the typical UObject mantra that all the fields are optional when deserializingcontinue;}if (JsonValue->IsValid() && !(*JsonValue)->IsNull()){void* Value = Property->ContainerPtrToValuePtr<uint8>(OutStruct);if (!JsonValueToUPropertyWithContainer(*JsonValue, Property, Value, nullptr, nullptr, CheckFlags, SkipFlags)){UE_LOG(LogJson, Error, TEXT("JsonObjectToUStruct - Unable to parse %s.%s from JSON"), *StructDefinition->GetName(), *Property->GetName());return false;}}if (--NumUnclaimedProperties <= 0){// If we found all properties that were in the JsonAttributes map, there is no reason to keep looking for more.break;}}return true;
}/** Convert JSON to property, assuming either the property is not an array or the value is an individual array element */
bool UJsonOperateLibrary::JsonValueToUPropertyWithContainer(const TSharedPtr<FJsonValue>& JsonValue, UProperty* Property, void* OutValue, const UStruct* ContainerStruct, void* Container, int64 CheckFlags, int64 SkipFlags)
{if (!JsonValue.IsValid()){UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - Invalid value JSON key"));return false;}bool bArrayOrSetProperty = Property->IsA<UArrayProperty>() || Property->IsA<USetProperty>();bool bJsonArray = JsonValue->Type == EJson::Array;if (!bJsonArray){if (bArrayOrSetProperty){UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - Attempted to import TArray from non-array JSON key"));return false;}if (Property->ArrayDim != 1){UE_LOG(LogJson, Warning, TEXT("Ignoring excess properties when deserializing %s"), *Property->GetName());}return ConvertScalarJsonValueToUPropertyWithContainer(JsonValue, Property, OutValue, ContainerStruct, Container, CheckFlags, SkipFlags);}// In practice, the ArrayDim == 1 check ought to be redundant, since nested arrays of UPropertys are not supportedif (bArrayOrSetProperty && Property->ArrayDim == 1){// Read into TArrayreturn ConvertScalarJsonValueToUPropertyWithContainer(JsonValue, Property, OutValue, ContainerStruct, Container, CheckFlags, SkipFlags);}// We're deserializing a JSON arrayconst auto& ArrayValue = JsonValue->AsArray();if (Property->ArrayDim < ArrayValue.Num()){UE_LOG(LogJson, Warning, TEXT("Ignoring excess properties when deserializing %s"), *Property->GetName());}// Read into native arrayint ItemsToRead = FMath::Clamp(ArrayValue.Num(), 0, Property->ArrayDim);for (int Index = 0; Index != ItemsToRead; ++Index){if (!ConvertScalarJsonValueToUPropertyWithContainer(ArrayValue[Index], Property, (char*)OutValue + Index * Property->ElementSize, ContainerStruct, Container, CheckFlags, SkipFlags)){return false;}}return true;
}bool UJsonOperateLibrary::ConvertScalarJsonValueToUPropertyWithContainer(const TSharedPtr<FJsonValue>& JsonValue, UProperty* Property, void* OutValue, const UStruct* ContainerStruct, void* Container, int64 CheckFlags, int64 SkipFlags)
{if (UEnumProperty * EnumProperty = Cast<UEnumProperty>(Property)){if (JsonValue->Type == EJson::String){// see if we were passed a string for the enumconst UEnum* Enum = EnumProperty->GetEnum();check(Enum);FString StrValue = JsonValue->AsString();int64 IntValue = Enum->GetValueByName(FName(*StrValue));if (IntValue == INDEX_NONE){UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - Unable import enum %s from string value %s for property %s"), *Enum->CppType, *StrValue, *Property->GetNameCPP());return false;}EnumProperty->GetUnderlyingProperty()->SetIntPropertyValue(OutValue, IntValue);}else{// AsNumber will log an error for completely inappropriate types (then give us a default)EnumProperty->GetUnderlyingProperty()->SetIntPropertyValue(OutValue, (int64)JsonValue->AsNumber());}}else if (UNumericProperty * NumericProperty = Cast<UNumericProperty>(Property)){if (NumericProperty->IsEnum() && JsonValue->Type == EJson::String){// see if we were passed a string for the enumconst UEnum* Enum = NumericProperty->GetIntPropertyEnum();check(Enum); // should be assured by IsEnum()FString StrValue = JsonValue->AsString();int64 IntValue = Enum->GetValueByName(FName(*StrValue));if (IntValue == INDEX_NONE){UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - Unable import enum %s from string value %s for property %s"), *Enum->CppType, *StrValue, *Property->GetNameCPP());return false;}NumericProperty->SetIntPropertyValue(OutValue, IntValue);}else if (NumericProperty->IsFloatingPoint()){// AsNumber will log an error for completely inappropriate types (then give us a default)NumericProperty->SetFloatingPointPropertyValue(OutValue, JsonValue->AsNumber());}else if (NumericProperty->IsInteger()){if (JsonValue->Type == EJson::String){// parse string -> int64 ourselves so we don't lose any precision going through AsNumber (aka double)NumericProperty->SetIntPropertyValue(OutValue, FCString::Atoi64(*JsonValue->AsString()));}else{// AsNumber will log an error for completely inappropriate types (then give us a default)NumericProperty->SetIntPropertyValue(OutValue, (int64)JsonValue->AsNumber());}}else{UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - Unable to set numeric property type %s for property %s"), *Property->GetClass()->GetName(), *Property->GetNameCPP());return false;}}else if (UBoolProperty * BoolProperty = Cast<UBoolProperty>(Property)){// AsBool will log an error for completely inappropriate types (then give us a default)BoolProperty->SetPropertyValue(OutValue, JsonValue->AsBool());}else if (UStrProperty * StringProperty = Cast<UStrProperty>(Property)){// AsString will log an error for completely inappropriate types (then give us a default)StringProperty->SetPropertyValue(OutValue, JsonValue->AsString());}else if (UArrayProperty * ArrayProperty = Cast<UArrayProperty>(Property)){if (JsonValue->Type == EJson::Array){TArray< TSharedPtr<FJsonValue> > ArrayValue = JsonValue->AsArray();int32 ArrLen = ArrayValue.Num();// make the output array size matchFScriptArrayHelper Helper(ArrayProperty, OutValue);Helper.Resize(ArrLen);// set the property valuesfor (int32 i = 0; i < ArrLen; ++i){const TSharedPtr<FJsonValue>& ArrayValueItem = ArrayValue[i];if (ArrayValueItem.IsValid() && !ArrayValueItem->IsNull()){if (!JsonValueToUPropertyWithContainer(ArrayValueItem, ArrayProperty->Inner, Helper.GetRawPtr(i), ContainerStruct, Container, CheckFlags & (~CPF_ParmFlags), SkipFlags)){UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - Unable to deserialize array element [%d] for property %s"), i, *Property->GetNameCPP());return false;}}}}else{UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - Attempted to import TArray from non-array JSON key for property %s"), *Property->GetNameCPP());return false;}}else if (UMapProperty * MapProperty = Cast<UMapProperty>(Property)){if (JsonValue->Type == EJson::Object){TSharedPtr<FJsonObject> ObjectValue = JsonValue->AsObject();FScriptMapHelper Helper(MapProperty, OutValue);check(ObjectValue);int32 MapSize = ObjectValue->Values.Num();Helper.EmptyValues(MapSize);// set the property valuesfor (const auto& Entry : ObjectValue->Values){if (Entry.Value.IsValid() && !Entry.Value->IsNull()){int32 NewIndex = Helper.AddDefaultValue_Invalid_NeedsRehash();TSharedPtr<FJsonValueString> TempKeyValue = MakeShared<FJsonValueString>(Entry.Key);const bool bKeySuccess = JsonValueToUPropertyWithContainer(TempKeyValue, MapProperty->KeyProp, Helper.GetKeyPtr(NewIndex), ContainerStruct, Container, CheckFlags & (~CPF_ParmFlags), SkipFlags);const bool bValueSuccess = JsonValueToUPropertyWithContainer(Entry.Value, MapProperty->ValueProp, Helper.GetValuePtr(NewIndex), ContainerStruct, Container, CheckFlags & (~CPF_ParmFlags), SkipFlags);if (!(bKeySuccess && bValueSuccess)){UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - Unable to deserialize map element [key: %s] for property %s"), *Entry.Key, *Property->GetNameCPP());return false;}}}Helper.Rehash();}else{UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - Attempted to import TMap from non-object JSON key for property %s"), *Property->GetNameCPP());return false;}}else if (USetProperty * SetProperty = Cast<USetProperty>(Property)){if (JsonValue->Type == EJson::Array){TArray< TSharedPtr<FJsonValue> > ArrayValue = JsonValue->AsArray();int32 ArrLen = ArrayValue.Num();FScriptSetHelper Helper(SetProperty, OutValue);// set the property valuesfor (int32 i = 0; i < ArrLen; ++i){const TSharedPtr<FJsonValue>& ArrayValueItem = ArrayValue[i];if (ArrayValueItem.IsValid() && !ArrayValueItem->IsNull()){int32 NewIndex = Helper.AddDefaultValue_Invalid_NeedsRehash();if (!JsonValueToUPropertyWithContainer(ArrayValueItem, SetProperty->ElementProp, Helper.GetElementPtr(NewIndex), ContainerStruct, Container, CheckFlags & (~CPF_ParmFlags), SkipFlags)){UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - Unable to deserialize set element [%d] for property %s"), i, *Property->GetNameCPP());return false;}}}Helper.Rehash();}else{UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - Attempted to import TSet from non-array JSON key for property %s"), *Property->GetNameCPP());return false;}}else if (UTextProperty * TextProperty = Cast<UTextProperty>(Property)){if (JsonValue->Type == EJson::String){// assume this string is already localized, so import as invariantTextProperty->SetPropertyValue(OutValue, FText::FromString(JsonValue->AsString()));}else if (JsonValue->Type == EJson::Object){TSharedPtr<FJsonObject> Obj = JsonValue->AsObject();check(Obj.IsValid()); // should not fail if Type == EJson::Object// import the subvalue as a culture invariant stringFText Text;if (!FJsonObjectConverter::GetTextFromObject(Obj.ToSharedRef(), Text)){UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - Attempted to import FText from JSON object with invalid keys for property %s"), *Property->GetNameCPP());return false;}TextProperty->SetPropertyValue(OutValue, Text);}else{UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - Attempted to import FText from JSON that was neither string nor object for property %s"), *Property->GetNameCPP());return false;}}else if (UStructProperty * StructProperty = Cast<UStructProperty>(Property)){static const FName NAME_DateTime(TEXT("DateTime"));static const FName NAME_Color(TEXT("Color"));static const FName NAME_LinearColor(TEXT("LinearColor"));if (JsonValue->Type == EJson::Object){TSharedPtr<FJsonObject> Obj = JsonValue->AsObject();check(Obj.IsValid()); // should not fail if Type == EJson::Objectif (!JsonAttributesToUStructWithContainer(Obj->Values, StructProperty->Struct, OutValue, ContainerStruct, Container, CheckFlags & (~CPF_ParmFlags), SkipFlags)){UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - FJsonObjectConverter::JsonObjectToUStruct failed for property %s"), *Property->GetNameCPP());return false;}}else if (JsonValue->Type == EJson::String && StructProperty->Struct->GetFName() == NAME_LinearColor){FLinearColor& ColorOut = *(FLinearColor*)OutValue;FString ColorString = JsonValue->AsString();FColor IntermediateColor;IntermediateColor = FColor::FromHex(ColorString);ColorOut = IntermediateColor;}else if (JsonValue->Type == EJson::String && StructProperty->Struct->GetFName() == NAME_Color){FColor& ColorOut = *(FColor*)OutValue;FString ColorString = JsonValue->AsString();ColorOut = FColor::FromHex(ColorString);}else if (JsonValue->Type == EJson::String && StructProperty->Struct->GetFName() == NAME_DateTime){FString DateString = JsonValue->AsString();FDateTime& DateTimeOut = *(FDateTime*)OutValue;if (DateString == TEXT("min")){// min representable value for our date struct. Actual date may vary by platform (this is used for sorting)DateTimeOut = FDateTime::MinValue();}else if (DateString == TEXT("max")){// max representable value for our date struct. Actual date may vary by platform (this is used for sorting)DateTimeOut = FDateTime::MaxValue();}else if (DateString == TEXT("now")){// this value's not really meaningful from json serialization (since we don't know timezone) but handle it anyway since we're handling the other keywordsDateTimeOut = FDateTime::UtcNow();}else if (FDateTime::ParseIso8601(*DateString, DateTimeOut)){// ok}else if (FDateTime::Parse(DateString, DateTimeOut)){// ok}else{UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - Unable to import FDateTime for property %s"), *Property->GetNameCPP());return false;}}else if (JsonValue->Type == EJson::String && StructProperty->Struct->GetCppStructOps() && StructProperty->Struct->GetCppStructOps()->HasImportTextItem()){UScriptStruct::ICppStructOps* TheCppStructOps = StructProperty->Struct->GetCppStructOps();FString ImportTextString = JsonValue->AsString();const TCHAR* ImportTextPtr = *ImportTextString;if (!TheCppStructOps->ImportTextItem(ImportTextPtr, OutValue, 0x00000000, nullptr, (FOutputDevice*)GWarn)){// Fall back to trying the tagged property approach if custom ImportTextItem couldn't get it doneProperty->ImportText(ImportTextPtr, OutValue, 0x00000000, nullptr);}}else if (JsonValue->Type == EJson::String){FString ImportTextString = JsonValue->AsString();const TCHAR* ImportTextPtr = *ImportTextString;Property->ImportText(ImportTextPtr, OutValue, 0x00000000, nullptr);}else{UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - Attempted to import UStruct from non-object JSON key for property %s"), *Property->GetNameCPP());return false;}}else if (UObjectProperty * ObjectProperty = Cast<UObjectProperty>(Property)){if (JsonValue->Type == EJson::Object){UObject* Outer = GetTransientPackage();if (ContainerStruct->IsChildOf(UObject::StaticClass())){Outer = (UObject*)Container;}UClass* PropertyClass = ObjectProperty->PropertyClass;UObject* createdObj = StaticAllocateObject(PropertyClass, Outer, NAME_None, EObjectFlags::RF_NoFlags, EInternalObjectFlags::None, false);(*PropertyClass->ClassConstructor)(FObjectInitializer(createdObj, PropertyClass->ClassDefaultObject, false, false));ObjectProperty->SetObjectPropertyValue(OutValue, createdObj);TSharedPtr<FJsonObject> Obj = JsonValue->AsObject();check(Obj.IsValid()); // should not fail if Type == EJson::Objectif (!JsonAttributesToUStructWithContainer(Obj->Values, ObjectProperty->PropertyClass, createdObj, ObjectProperty->PropertyClass, createdObj, CheckFlags & (~CPF_ParmFlags), SkipFlags)){UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - FJsonObjectConverter::JsonObjectToUStruct failed for property %s"), *Property->GetNameCPP());return false;}}else if (JsonValue->Type == EJson::String){// Default to expect a string for everything elseif (Property->ImportText(*JsonValue->AsString(), OutValue, 0, NULL) == NULL){UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - Unable import property type %s from string value for property %s"), *Property->GetClass()->GetName(), *Property->GetNameCPP());return false;}}}else{// Default to expect a string for everything elseif (Property->ImportText(*JsonValue->AsString(), OutValue, 0, NULL) == NULL){UE_LOG(LogJson, Error, TEXT("JsonValueToUProperty - Unable import property type %s from string value for property %s"), *Property->GetClass()->GetName(), *Property->GetNameCPP());return false;}}return true;
}bool UJsonOperateLibrary::UStructToJsonAttributes(const UStruct* StructDefinition, const void* Struct, TMap< FString, TSharedPtr<FJsonValue> >& OutJsonAttributes, int64 CheckFlags, int64 SkipFlags)
{if (SkipFlags == 0){// If we have no specified skip flags, skip deprecated, transient and skip serialization by default when writingSkipFlags |= CPF_Deprecated | CPF_Transient;}if (StructDefinition == FJsonObjectWrapper::StaticStruct()){// Just copy it into the objectconst FJsonObjectWrapper* ProxyObject = (const FJsonObjectWrapper*)Struct;if (ProxyObject->JsonObject.IsValid()){OutJsonAttributes = ProxyObject->JsonObject->Values;}return true;}for (TFieldIterator<UProperty> It(StructDefinition); It; ++It){UProperty* Property = *It;// Check to see if we should ignore this propertyif (CheckFlags != 0 && !Property->HasAnyPropertyFlags(CheckFlags)){continue;}if (Property->HasAnyPropertyFlags(SkipFlags)){continue;}FString VariableName = FJsonObjectConverter::StandardizeCase(GetShortName(Property));const void* Value = Property->ContainerPtrToValuePtr<uint8>(Struct);// convert the property to a FJsonValueTSharedPtr<FJsonValue> JsonValue = UPropertyToJsonValue(Property, Value, CheckFlags, SkipFlags);if (!JsonValue.IsValid()){UClass* PropClass = Property->GetClass();UE_LOG(LogJson, Error, TEXT("UStructToJsonObject - Unhandled property type '%s': %s"), *PropClass->GetName(), *Property->GetPathName());return false;}// set the value on the output objectOutJsonAttributes.Add(VariableName, JsonValue);}return true;
}TSharedPtr<FJsonValue> UJsonOperateLibrary::UPropertyToJsonValue(UProperty* Property, const void* Value, int64 CheckFlags, int64 SkipFlags)
{if (Property->ArrayDim == 1){return ConvertScalarUPropertyToJsonValue(Property, Value, CheckFlags, SkipFlags);}TArray< TSharedPtr<FJsonValue> > Array;for (int Index = 0; Index != Property->ArrayDim; ++Index){Array.Add(ConvertScalarUPropertyToJsonValue(Property, (char*)Value + Index * Property->ElementSize, CheckFlags, SkipFlags));}return MakeShared<FJsonValueArray>(Array);
}/** Convert property to JSON, assuming either the property is not an array or the value is an individual array element */
TSharedPtr<FJsonValue> UJsonOperateLibrary::ConvertScalarUPropertyToJsonValue(UProperty* Property, const void* Value, int64 CheckFlags, int64 SkipFlags)
{if (UEnumProperty * EnumProperty = Cast<UEnumProperty>(Property)){// export enums as stringsUEnum* EnumDef = EnumProperty->GetEnum();FString StringValue = EnumDef->GetNameStringByValue(EnumProperty->GetUnderlyingProperty()->GetSignedIntPropertyValue(Value));return MakeShared<FJsonValueString>(StringValue);}else if (UNumericProperty * NumericProperty = Cast<UNumericProperty>(Property)){// see if it's an enumUEnum* EnumDef = NumericProperty->GetIntPropertyEnum();if (EnumDef != NULL){// export enums as stringsFString StringValue = EnumDef->GetNameStringByValue(NumericProperty->GetSignedIntPropertyValue(Value));return MakeShared<FJsonValueString>(StringValue);}// We want to export numbers as numbersif (NumericProperty->IsFloatingPoint()){return MakeShared<FJsonValueNumber>(NumericProperty->GetFloatingPointPropertyValue(Value));}else if (NumericProperty->IsInteger()){return MakeShared<FJsonValueNumber>(NumericProperty->GetSignedIntPropertyValue(Value));}// fall through to default}else if (UBoolProperty * BoolProperty = Cast<UBoolProperty>(Property)){// Export bools as boolsreturn MakeShared<FJsonValueBoolean>(BoolProperty->GetPropertyValue(Value));}else if (UStrProperty * StringProperty = Cast<UStrProperty>(Property)){return MakeShared<FJsonValueString>(StringProperty->GetPropertyValue(Value));}else if (UTextProperty * TextProperty = Cast<UTextProperty>(Property)){return MakeShared<FJsonValueString>(TextProperty->GetPropertyValue(Value).ToString());}else if (UArrayProperty * ArrayProperty = Cast<UArrayProperty>(Property)){TArray< TSharedPtr<FJsonValue> > Out;FScriptArrayHelper Helper(ArrayProperty, Value);for (int32 i = 0, n = Helper.Num(); i < n; ++i){TSharedPtr<FJsonValue> Elem = UPropertyToJsonValue(ArrayProperty->Inner, Helper.GetRawPtr(i), CheckFlags & (~CPF_ParmFlags), SkipFlags);if (Elem.IsValid()){// add to the arrayOut.Push(Elem);}}return MakeShared<FJsonValueArray>(Out);}else if (USetProperty * SetProperty = Cast<USetProperty>(Property)){TArray< TSharedPtr<FJsonValue> > Out;FScriptSetHelper Helper(SetProperty, Value);for (int32 i = 0, n = Helper.Num(); n; ++i){if (Helper.IsValidIndex(i)){TSharedPtr<FJsonValue> Elem = UPropertyToJsonValue(SetProperty->ElementProp, Helper.GetElementPtr(i), CheckFlags & (~CPF_ParmFlags), SkipFlags);if (Elem.IsValid()){// add to the arrayOut.Push(Elem);}--n;}}return MakeShared<FJsonValueArray>(Out);}else if (UMapProperty * MapProperty = Cast<UMapProperty>(Property)){TSharedRef<FJsonObject> Out = MakeShared<FJsonObject>();FScriptMapHelper Helper(MapProperty, Value);for (int32 i = 0, n = Helper.Num(); n; ++i){if (Helper.IsValidIndex(i)){TSharedPtr<FJsonValue> KeyElement = UPropertyToJsonValue(MapProperty->KeyProp, Helper.GetKeyPtr(i), CheckFlags & (~CPF_ParmFlags), SkipFlags);TSharedPtr<FJsonValue> ValueElement = UPropertyToJsonValue(MapProperty->ValueProp, Helper.GetValuePtr(i), CheckFlags & (~CPF_ParmFlags), SkipFlags);if (KeyElement.IsValid() && ValueElement.IsValid()){FString KeyString;if (!KeyElement->TryGetString(KeyString)){MapProperty->KeyProp->ExportTextItem(KeyString, Helper.GetKeyPtr(i), nullptr, nullptr, 0);if (KeyString.IsEmpty()){UE_LOG(LogJson, Error, TEXT("Unable to convert key to string for property %s."), *MapProperty->GetName())KeyString = FString::Printf(TEXT("Unparsed Key %d"), i);}}Out->SetField(KeyString, ValueElement);}--n;}}return MakeShared<FJsonValueObject>(Out);}else if (UStructProperty * StructProperty = Cast<UStructProperty>(Property)){UScriptStruct::ICppStructOps* TheCppStructOps = StructProperty->Struct->GetCppStructOps();// Intentionally exclude the JSON Object wrapper, which specifically needs to export JSON in an object representation instead of a stringif (StructProperty->Struct != FJsonObjectWrapper::StaticStruct() && TheCppStructOps && TheCppStructOps->HasExportTextItem()){FString OutValueStr;TheCppStructOps->ExportTextItem(OutValueStr, Value, nullptr, nullptr, 0x00000000, nullptr);return MakeShared<FJsonValueString>(OutValueStr);}TSharedRef<FJsonObject> Out = MakeShared<FJsonObject>();if (UStructToJsonAttributes(StructProperty->Struct, Value, Out->Values, CheckFlags & (~CPF_ParmFlags), SkipFlags)){return MakeShared<FJsonValueObject>(Out);}// fall through to default}else{// Default to export as string for everything elseFString StringValue;Property->ExportTextItem(StringValue, Value, NULL, NULL, 0x00000000);return MakeShared<FJsonValueString>(StringValue);}// invalidreturn TSharedPtr<FJsonValue>();
}

参考：

https://blog.csdn.net/justtestlike/article/details/84300154

https://docs.unrealengine.com/en-US/API/Runtime/JsonUtilities/FJsonObjectConverter/index.html

https://blog.csdn.net/u012999985/article/details/52902065

https://docs.unrealengine.com/zh-CN/Programming/UnrealArchitecture/Reference/Functions/Specifiers/index.html

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