Custom File Type

Files in the simulator are UObject classes based on UOperatingSystemFile. When the player double-clicks a file in Explorer, the OS spawns the file’s widget and/or launches the Target Program Class.

Bundled examples:

Class	Extension	Opens with
UOperatingSystemVideoFile	`.mp4`, etc.	Video Player
UOperatingSystemAudioFile	`.mp3`, etc.	Audio Player

flowchart TB
  subgraph row1[" "]
    direction LR
    File["UOperatingSystemFile subclass"] --> Ext["Extension + IconObject"] --> Prog["TargetProgramClass"]
  end
  subgraph row2[" "]
    direction LR
    Explorer["UOperatingSystemExplorer double-click"] --> Open["On Open → launch UOperatingSystemBaseProgram"]
  end
  Explorer --> File
  File --> Open

Blueprint file type

1. Create the file class

Content Browser → Blueprint Class → Operating System File
Name it BP_File_MyDoc
Set properties:

Property	Example
Name	`My Document` (display; instance name set at runtime)
Extension	`.mydoc`
Icon Object	Your texture or UI material
Target Program Class	Your program Blueprint
Icon Widget Class	`WBP_FileIcon` (duplicate from plugin)
Widget Class	Optional preview widget

2. Create file instances at runtime

Use Construct File on your program or OS static helpers from UOperatingSystemStatics to place files in a directory.

Blueprint pattern:

Get Operating System → Get Directory by Path
  → Construct File (Class: BP_File_MyDoc, Parent Directory: …)

3. Handle open

Override On Open on the file Blueprint to run custom logic before the target program launches.

C++ file type

UCLASS()
class UMyDocumentFile : public UOperatingSystemFile
{
    GENERATED_BODY()

public:
    UMyDocumentFile()
    {
        Extension = FText::FromString(TEXT(".mydoc"));
    }

protected:
    virtual void OnOpen() override;
};

File + program pairing

For programs that create files (like Mail or Video Player), also define:

A Data Class on the program (UOperatingSystemProgramData)
File construction in the program’s install or save logic

See Video Player file and Audio Player file for full examples.