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# QLPreviewControllerDataSource

The protocol that a data source for a preview controller needs to adopt to provide preview items to the controller.

```
@MainActor protocol QLPreviewControllerDataSource
```

## Overview

Besides providing a [`QLPreviewController`](/documentation/QuickLook/QLPreviewController) with items to preview, this protocol is responsible for telling the preview controller how many items it needs to include in a preview item navigation list.

## Topics

### Providing data to a preview controller

[`-  numberOfPreviewItemsInPreviewController:`](/documentation/QuickLook/QLPreviewControllerDataSource/numberOfPreviewItems(in:))

Returns the number of preview items to include in the preview navigation list.

[`-  previewController:previewItemAtIndex:`](/documentation/QuickLook/QLPreviewControllerDataSource/previewController(_:previewItemAt:))

Returns the preview item that the controller displays for the specified index.


---

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