Working with Blueprint (BP) in Unreal Engine

Compile Blueprint asset with C++

/**
 * Editor Only - Will not work in packaged build.
 *
 * <mark>Compile a blueprint asset</mark>
 *
 * @param BlueprintPath	Path of the blueprint: "/Game/Folder/MyBp"
 * @param OutInfoMsg	More information about the action's result
 * @param return If the action was a success or not
 */
UFUNCTION(BlueprintCallable, Category = "<a href="https://www.youtube.com/watch?v=WNSLXtrfSns" target="_blank">Alex Quevillon | Compile Blueprint</a>")
static void CompileBlueprint(FString BlueprintPath, FString& OutInfoMsg);

#include "Kismet2/KismetEditorUtilities.h" // UnrealEd (Editor Only)
#include "Kismet2/CompilerResultsLog.h" // UnrealEd (Editor Only)

bool UExampleClass::CompileBlueprint(FString BlueprintPath, FString& OutInfoMsg)
{
  // Load blueprint asset
  UBlueprint* Blueprint = Cast<UBlueprint>(StaticLoadObject(UBlueprint::StaticClass(), nullptr, *BlueprintPath));
	
  if (Blueprint == nullptr)
  {
    OutInfoMsg = FString::Printf(TEXT("Compile Blueprint Failed - Path doesn't lead to a valid Blueprint. '%s'"), *BlueprintPath);
    return false;
  }
	
  // Compile blueprint
  FCompilerResultsLog Result;
  FKismetEditorUtilities::CompileBlueprint(Blueprint, EBlueprintCompileOptions::SkipSave, &Result);

  // Format the result
  FString Logs = Result.Messages.Num() > Result.NumWarnings + Result.NumErrors ? "
--- Logs ---" : "";
  FString Warnings = Result.NumWarnings > 0 ? "
--- Warnings ---" : "";
  FString Errors = Result.NumErrors > 0 ? "
--- Errors ---" : "";

  for (TSharedRef<FTokenizedMessage> Message : Result.Messages)
  {
    switch (Message.Get().GetSeverity())
    {
    default:
    case EMessageSeverity::Type::Info:
      Logs += "
" + Message.Get().ToText().ToString();
      break;
    case EMessageSeverity::Type::Warning:
    case EMessageSeverity::Type::PerformanceWarning:
    	Warnings += "
" + Message.Get().ToText().ToString();
    	break;
    case EMessageSeverity::Type::Error:
    	Errors += "
" + Message.Get().ToText().ToString();
    	break;
    }
  }

  // Return the result
  bool bSuccess = Result.NumErrors == 0;
  FString SucceededOrFailed = bSuccess ? "Succeeded" : "Failed";
  FString Messages = Logs + Warnings + Errors;
  OutInfoMsg = FString::Printf(TEXT("Compile Blueprint %s - '%s' %s"), *SucceededOrFailed, *BlueprintPath, *Messages);
  <strong>return bSuccess</strong>;
}

PrivateDependencyModuleNames.AddRange
(
  new string[] 
  { 
    // Default Modules
    "Core", 
    "CoreUObject", 
    "Engine", 

    // New Modules - Editor Only
    <mark>"UnrealEd"</mark>,
  }
);

Spawn Actor to any Blueprint

AddNodeToBlueprint defined below will be used by functions adding various kind of actors into any blueprint based on its BlueprintPath.

This way of adding any Actor to any Blueprint comes in handy if we need to extend 1 or more Bluperint actors from one place - e.g. during automatization process. If we code a C++ class, from which a blueprint asset is inherited, adding actors to blueprint is easy to do through the common way.

Add a component node to a blueprint asset (Help function)

/**
 * Editor Only - Will not work in packaged build.
 *
 * Add a component node to a blueprint asset
 *
 * @param BlueprintPath Path of the blueprint: "/Game/Folder/MyBp"
 * @param ComponentTemplate The component to use as a template when creating the node
 * @param ParentNodeName  The name of the desired parent node
 * @param bOutSuccess If the action was a success or not
 * @param OutInfoMsg  More information about the action's result
 * 
 * @return The node that was created
 */
UFUNCTION(BlueprintCallable, Category = "<a href="https://www.youtube.com/watch?v=KpQYzYwJJQ0" target="_blank">Add Components To Blueprint</a>")
static class USCS_Node* AddNodeToBlueprint(FString BlueprintPath, class USceneComponent* ComponentTemplate, FString ParentNodeName, bool& bOutSuccess, FString& OutInfoMsg);

#include "Engine/SCS_Node.h" // Engine
#include "Kismet2/BlueprintEditorUtils.h" // UnrealEd (Editor Only)

USCS_Node* UExampleClass::AddNodeToBlueprint(FString BlueprintPath, USceneComponent* ComponentTemplate, FString ParentNodeName, bool& bOutSuccess, FString& OutInfoMsg)
{
 // Load blueprint asset
 UBlueprint* Blueprint = Cast<UBlueprint>(StaticLoadObject(UBlueprint::StaticClass(), nullptr, *BlueprintPath));

 if (Blueprint == nullptr)
 {
		bOutSuccess = false;
		OutInfoMsg = FString::Printf(TEXT("Add Node To Blueprint Failed - Path doesn't lead to a valid Blueprint. '%s'"), *BlueprintPath);
		return nullptr;
 }

 // Create new node in blueprint asset
 USCS_Node* NewNode = <mark>Blueprint-&gt;SimpleConstructionScript</mark>-&gt;CreateNode(ComponentTemplate-&gt;GetClass(), *ComponentTemplate-&gt;GetName());

 // Parent node
 USCS_Node* ParentNode = Blueprint-&gt;SimpleConstructionScript-&gt;FindSCSNode(*ParentNodeName);
 if (ParentNode != nullptr) {
   ParentNode-&gt;AddChildNode(NewNode);
 } else {
   TArray&lt;USCS_Node*&gt; AllNodes = Blueprint-&gt;SimpleConstructionScript-&gt;GetAllNodes();
   // If there are no nodes in the blueprint or if the root node is still the default node
   if (AllNodes.Num() == 0 || AllNodes[0] == Blueprint-&gt;SimpleConstructionScript-&gt;GetDefaultSceneRootNode()) {
   	// Use this component as root node
   	Blueprint-&gt;SimpleConstructionScript-&gt;AddNode(NewNode);
   } else {
   	// Use the first node as parent (root node)
   	AllNodes[0]-&gt;AddChildNode(NewNode);
   }
 }

 // Copy component's settings onto node
 UEditorEngine::CopyPropertiesForUnrelatedObjects(ComponentTemplate, NewNode-&gt;ComponentTemplate);

 // Notify the engine we modified the blueprint components
 FBlueprintEditorUtils::MarkBlueprintAsStructurallyModified(Blueprint);

 // Return new node
 bOutSuccess = true;
 OutInfoMsg = FString::Printf(TEXT("Add Node To Blueprint Succeeded - '%s'"), *BlueprintPath);
 <strong>return NewNode;</strong>
}

PrivateDependencyModuleNames.AddRange
(
  new string[] 
  { 
    // Default Modules
    "Core", 
    "CoreUObject", 
    "Engine", 

    // New Modules - Editor Only
    <mark>"UnrealEd"</mark>,
  }
);

• Add a scene component to a blueprint asset

  .h

  /**
   * Editor Only - Will not work in packaged build.
   *
   * Add a scene component to a blueprint asset
   *
   * @param BlueprintPath Path of the blueprint: "/Game/Folder/MyBp"
   * @param bOutSuccess If the action was a success or not
   * @param OutInfoMsg  More information about the action's result
   * 
   * @return The node that was created
   */
  UFUNCTION(BlueprintCallable, Category = "<a href="https://www.youtube.com/watch?v=KpQYzYwJJQ0" target="_blank">Add Components To Blueprint</a>")
  static class USCS_Node* AddSceneComponentToBlueprint(FString BlueprintPath, bool& bOutSuccess, FString& OutInfoMsg);

  .cpp

  .Build.cs

• Add a point light component to a blueprint asset

  .h

  	/**
   * Editor Only - Will not work in packaged build.
   *
   * Add a point light component to a blueprint asset
   *
   * @param BlueprintPath Path of the blueprint: "/Game/Folder/MyBp"
   * @param bOutSuccess If the action was a success or not
   * @param OutInfoMsg  More information about the action's result
   * 
   * @return The node that was created
   */
  UFUNCTION(BlueprintCallable, Category = "<a href="https://www.youtube.com/watch?v=KpQYzYwJJQ0" target="_blank">Add Components To Blueprint</a>")
  static class USCS_Node* AddPointLightComponentToBlueprint(FString BlueprintPath, bool& bOutSuccess, FString& OutInfoMsg);

  .cpp

  .Build.cs

• Add a camera component to a blueprint asset

  .h

  /**
   * Editor Only - Will not work in packaged build.
   *
   * Add a camera component to a blueprint asset
   *
   * @param BlueprintPath Path of the blueprint: "/Game/Folder/MyBp"
   * @param bOutSuccess If the action was a success or not
   * @param OutInfoMsg  More information about the action's result
   * 
   * @return The node that was created
   */
  UFUNCTION(BlueprintCallable, Category = "<a href="https://www.youtube.com/watch?v=KpQYzYwJJQ0" target="_blank">Add Components To Blueprint</a>")
  static class USCS_Node* AddCameraComponentToBlueprint(FString BlueprintPath, bool& bOutSuccess, FString& OutInfoMsg);

  .cpp

  .Build.cs