ue4 C++ json数据的读写

这是改变恢复机制的json文件的例子 

//写入

TSharedPtr<FJsonObject> RootObject = MakeShareable(newFJsonObject);

TArray< TSharedPtr<FJsonValue> > PackagesThatCanBeRestored;

TSharedPtr<FJsonObject> EntryObject = MakeShareable(new FJsonObject);

EntryObject->SetStringField(TEXT("PackagePathName"), TEXT("Temp/Untitled_1"));

EntryObject->SetStringField(TEXT("AutoSavePath"), TEXT("Temp/Untitled_1_Auto1.umap"));

TSharedPtr<FJsonValue> EntryValue = MakeShareable(new FJsonValueObject(EntryObject));

PackagesThatCanBeRestored.Add(EntryValue);

RootObject->SetBoolField(TEXT("RestoreEnabled"), true);

RootObject->SetArrayField(TEXT("Packages"), PackagesThatCanBeRestored);

constFStringFilename = FPaths::GameSavedDir() /TEXT("Autosaves") /TEXT("PackageRestoreData.json");

FArchive* constFileAr = IFileManager::Get().CreateFileWriter(*Filename, FILEWRITE_EvenIfReadOnly);

if (FileAr)

{

     TSharedRef<TJsonWriter< TCHAR, TPrettyJsonPrintPolicy<TCHAR> >> Writer = TJsonWriterFactory< TCHAR, TPrettyJsonPrintPolicy<TCHAR> >::Create(FileAr);  

     FJsonSerializer::Serialize(RootObject.ToSharedRef(), Writer);

     FileAr->Close();

}

// 读取本地json文件

       const FString Filename = FPaths::GameSavedDir() / TEXT("Autosaves") / TEXT("PackageRestoreData.json");

       FArchive* const FileAr = IFileManager::Get().CreateFileReader(*Filename);

       bool bJsonLoaded = false;

       TSharedPtr<FJsonObject> RootObject = MakeShareable(new FJsonObject);

       {

              TSharedRef<TJsonReader<TCHAR>> Reader = TJsonReaderFactory<TCHAR>::Create(FileAr);

              bJsonLoaded = FJsonSerializer::Deserialize(Reader, RootObject);

              FileAr->Close();

       }

       TMap<FString, FString> PackagesThatCanBeRestored;

       TArray< TSharedPtr<FJsonValue> > PackagesThatCanBeRestoredArray = RootObject->GetArrayField(TEXT("Packages"));

       int32 TiRen = RootObject->GetIntegerField(TEXT("TiRen"));

       for (auto It = PackagesThatCanBeRestoredArray.CreateConstIterator(); It; ++It)

       {

              TSharedPtr<FJsonObject> EntryObject = (*It)->AsObject();

              const FString PackagePathName = EntryObject->GetStringField(TEXT("PackagePathName"));

              const FString AutoSavePath = EntryObject->GetStringField(TEXT("AutoSavePath"));

              PackagesThatCanBeRestored.Add(PackagePathName, AutoSavePath);

       }

       for (auto It = PackagesThatCanBeRestored.CreateConstIterator(); It; ++It)

       {

              if (TiRen == 1)

              {

                     EditorStartupMap = FPaths::GameContentDir() / TEXT("Autosaves") / It->Value;

              }

              else

              {

                     EditorStartupMap = AutoSaveUtils::GetAutoSaveDir() / It->Value;

              }

       }