---
title: prepareWithDevice
framework: realitykit
role: symbol
role_heading: Instance Property
path: realitykit/arview/rendercallbacks-swift.struct/preparewithdevice
---

# prepareWithDevice

A callback function for doing initial setup work.

## Declaration

```swift
var prepareWithDevice: ((any MTLDevice) -> Void)?
```

## Mentioned in

Applying core image filters as a postprocess effect Implementing postprocess effects using Metal compute functions

## Discussion

Discussion If you assign a function to prepareWithDevice, RealityKit calls that function once, after it does its setup work, but before it renders the next frame. If you register a prepareWithDevice callback during app startup, RealityKit calls it before it renders the first frame. A callback function looks like this:     func myPostProcessSetupCallback(device: MTLDevice) {         // Handle setup work here.     } To register the function so RealityKit calls it, assign it to the prepareWithDevice property of the view’s renderCallbacks property. arView.renderCallbacks.prepareWithDevice = myPostProcessSetupCallback To remove the callback, assign nil. arView.renderCallbacks.prepareWithDevice = nil If you assign a new closure or function to the property after setting it to nil, RealityKit calls the new closure before it renders the next frame. In that case, avoid doing long-running tasks in the callback function to avoid rendering hitches.

## See Also

### Register callback closures

- [postProcess](realitykit/arview/rendercallbacks-swift.struct/postprocess.md)