Object reference variable is empty at runtime

Why: Your code reads from a '{ref}' reference, but nothing was assigned to it. UE5 doesn't error at compile time, but warns that the runtime access will crash with null-pointer. Fix: Wherever this BP spawns, set the reference via Spawn Actor From Class → Set Reference. If it should be set from outside, expose the variable (eye-icon = Instance Editable) so it's set in the level editor. Add an Is Valid? Branch before each read to gracefully handle null.

CreateDynamicMaterialInstance — create runtime modifiable material

UPrimitiveComponent method. Store result in variable and reuse. Create once in BeginPlay.

CreateDynamicMaterialInstance — create a runtime-editable material copy

Must call this before SetScalarParameterValue/SetVectorParameterValue. Store the result in a variable for reuse.

Blueprint

A visual scripting asset (.uasset) that defines runtime behavior without C++. Compiles to bytecode the engine executes.

Create dynamic material and animate a parameter at runtime

Pattern: EventBeginPlay → GetMesh → CreateDynamicMaterialInstance(ElementIndex=0) → SetVariable(DynMat=ReturnValue). Then on Tick or timer: SetScalarParameterValue(ParameterName='Opacity', Value=SinWave). Or for color: SetVectorParameterValue(ParameterName='Color', Value=MakeLinearColor). Key: CreateDynamicMaterialInstance is called on the COMPONENT (GetMesh), not the actor. Must store the result before using Set*ParameterValue. ParameterName MUST match the name in the Material asset exactly.

Instance

A live, runtime object of a class. Properties on an instance can differ from defaults set in the class.

Change material color at runtime using dynamic material instance

Pattern: BeginPlay → CreateDynamicMaterialInstance(MeshComponent, 0) → store as variable DynMat. On trigger → SetVectorParameterValue(DynMat, 'BaseColor', LinearColor). Create MID once in BeginPlay, reuse variable. Parameter name must match Material parameter exactly (case-sensitive).

SetTextureParameterValue on dynamic material — change texture parameter at runtime

SetText (widget) — update Text block content at runtime

Call on a TextBlock widget variable from your Widget BP. Use 'Format Text' or 'Conv_StringToText' to build the Text value.

Health and damage system with ApplyDamage and EventAnyDamage

Dealing damage: Event → ApplyDamage(TargetActor, BaseDamage, InstigatorController, DamageCauser, DamageTypeClass). Receiving: EventAnyDamage → Damage output → Subtract_FloatFloat(CurrentHealth, Damage) → FClamp(Result, 0, MaxHealth) → SET CurrentHealth → Branch(CurrentHealth <= 0) → True: DestroyActor. Initialize CurrentHealth=MaxHealth in BeginPlay.