---
title: "handle(_:forProperties:handler:)"
framework: scenekit
role: symbol
role_heading: Instance Method
path: "scenekit/scnparticlesystem/handle(_:forproperties:handler:)"
---

# handle(_:forProperties:handler:)

Adds a block that modifies particle properties, to be executed at a specified event in the lifetimes of particles in the system.

## Declaration

```swift
func handle(_ event: SCNParticleEvent, forProperties properties: [SCNParticleSystem.ParticleProperty], handler block: @escaping SCNParticleEventBlock)
```

## Parameters

- `event`: The event at which to call the block. See doc://com.apple.scenekit/documentation/SceneKit/SCNParticleEvent for allowed values.
- `properties`: An array containing one or more of the constants listed in Particle Property Keys, each of which specifies a property of the appearance or behaviors of particles in the particle system.
- `block`: A doc://com.apple.scenekit/documentation/SceneKit/SCNParticleEventBlock block to be called every time SceneKit renders a frame. In this block you can modify the properties of particles in the system.

## Discussion

Discussion By associating a block with one or more particle properties, you can run arbitrary code that modifies those properties when a significant event in the particle simulation occurs for one or more particles. For example, you can use the following code with a confetti effect to randomly switch between two distinct colors for each spawned particle: [system handleEvent:SCNParticleEventBirth       forProperties:@[SCNParticlePropertyColor]           withBlock:^(void **data, size_t *dataStride, uint32_t *indices , NSInteger count) {               for (NSInteger i = 0; i < count; ++i) {                   float *color = (float *)((char *)data[0] + dataStride[0] * i);                   if (rand() & 0x1) { // Switch the green and red color components.                       color[0] = color[1];                       color[1] = 0;                   }               }           }];

## See Also

### Modifying Particles in Response to Particle System Events

- [SCNParticleEvent](scenekit/scnparticleevent.md)
- [SCNParticleEventBlock](scenekit/scnparticleeventblock.md)