--- title: "Lazy load PDF annotations in Swift for iOS" canonical_url: "https://www.nutrient.io/guides/ios/samples/lazy-load-pdf-annotations/" md_url: "https://www.nutrient.io/guides/ios/samples/lazy-load-pdf-annotations.md" last_updated: "2026-05-25T12:14:42.940Z" description: "Discover how to create a custom annotation provider that lazily loads annotations from PDFs. Explore our guide for embedding annotations in iOS." --- # Lazy load PDF annotations in Swift for iOS A custom annotation provider that lazily loads its annotations and combines them with annotations from the PDF document. Get additional resources by visiting our guide on [embedding annotations in PDF in iOS](/guides/ios/annotations/save/embed-into-pdf.md). [Get Started](https://www.nutrient.io/sdk/ios/getting-started.md) [All Samples](https://www.nutrient.io/guides/ios/samples.md) [Download](https://www.nutrient.io/guides/ios/downloads.md) [Launch Demo](https://www.nutrient.io/demo/) --- ```swift // // Copyright © 2021-2026 PSPDFKit GmbH. All rights reserved. // // The Nutrient sample applications are licensed with a modified BSD license. // Please see License for details. This notice may not be removed from this file. // import PSPDFKit import PSPDFKitUI class CompoundAnnotationProviderExample: Example { override init() { super.init() contentDescription = "A custom annotation provider that lazily loads its annotations and combines them with annotations from the PDF document." category =.annotationProviders } override func invoke(with delegate: ExampleRunnerDelegate) -> UIViewController? { let document = AssetLoader.writableDocument(for:.welcome, overrideIfExists: true) document.didCreateDocumentProviderBlock = { documentProvider in if let fileAnnotationProvider = documentProvider.annotationManager.fileAnnotationProvider { documentProvider.annotationManager.annotationProviders = [ CompoundAnnotationProvider(documentProvider: documentProvider, fileAnnotationProvider: fileAnnotationProvider), ] } } return AdaptivePDFViewController(document: document) } } private class CompoundAnnotationProvider: PDFContainerAnnotationProvider { init(documentProvider: PDFDocumentProvider, fileAnnotationProvider: PDFFileAnnotationProvider) { self.fileAnnotationProvider = fileAnnotationProvider super.init(documentProvider: documentProvider) } /// Reference to the original file annotation provider. let fileAnnotationProvider: PDFFileAnnotationProvider /// Page indices for which we have lazily loaded the annotations. var loadedPageIndices: Set = [] override func annotationsForPage(at pageIndex: PageIndex) -> [Annotation]? { // First, fetch the annotations from the file annotation provider. Use // `annotationsForPage(at:)` because this is the function that actually // loads the annotations. let fileAnnotations = fileAnnotationProvider.annotationsForPage(at: pageIndex)?? [] // Then, merge them with the custom annotations. let customAnnotations = customAnnotationsForPage(at: pageIndex) return fileAnnotations + customAnnotations } private func customAnnotationsForPage(at pageIndex: PageIndex) -> [Annotation] { // If we loaded our custom annotations into the cache, ask `super` to // retrieve them from cache within the same critical region for reading // to achieve atomicity. let cachedCustomAnnotations = performRead { loadedPageIndices.contains(pageIndex)? super.annotationsForPage(at: pageIndex) : nil } if let cachedCustomAnnotations { return cachedCustomAnnotations } // Otherwise, we need to load the custom annotations and load them // into the cache. We need to do all that within a critical region. return performWriteAndWait { // Because we had to leave the critical region from reading to // writing, another thread could have raced here before us. In order // to prevent caching the same custom annotations multiple times, we // must check our bookkeeping first. Reads can be nested in writes, // so calling `super` here is fine. if loadedPageIndices.contains(pageIndex) { let cachedCustomAnnotations = super.annotationsForPage(at: pageIndex)?? [] return cachedCustomAnnotations } // For the sake of this example, we simulate loading annotations by // generating random squares. let loadedCustomAnnotations = makeSquares(at: pageIndex) // Because adding annotations to the cache can fail and the return // value can differ, we need to account for that when doing our // bookkeeping. guard let addedCustomAnnotations = super.add(loadedCustomAnnotations, options: nil) else { return [] } // Now that we know caching succeeded, do the bookkeeping and return // the added custom annotations. loadedPageIndices.insert(pageIndex) return addedCustomAnnotations } } override func add(_ annotations: [Annotation], options: [AnnotationManager.ChangeBehaviorKey: Any]? = nil) -> [Annotation]? { // For each annotation being added here, make sure we have loaded the // custom annotations at the page they're supposed to be on. for annotation in annotations { _ = customAnnotationsForPage(at: annotation.pageIndex) } return super.add(annotations, options: options) } override var allowAnnotationZIndexMoves: Bool { // Because this annotation provider merges annotations from two sources, // z-index moves could have unreliable results. It's better to disable // them altogether. false } override func insert(_ annotation: Annotation, atZIndex destinationIndex: UInt, options: [AnnotationManager.ChangeBehaviorKey: Any]? = nil) throws { // Since z-index moves are disabled, we should always throw here. throw PSPDFKitError(.cannotModifyAnnotationZIndices) } override var shouldSaveAnnotations: Bool { // Because this implementation doesn't actually load annotations from // any store, we don't support saving. false } override func saveAnnotations(options: [String: Any]? = nil) throws { // Since saving is disabled, we should always throw here. throw PSPDFKitError(.annotationSavingDisabled) // If your custom annotation store supports wtiting on a per-page basis, // and you don't do that immediately when adding annotations, you will // have to make sure that the custom annotations for all pages have been // cached before. In any case, any actual saving operation would need to // be wrapped in its entirety in a critical region for writing, using // `performWriteAndWait`. } } private func makeSquares(at pageIndex: PageIndex) -> [SquareAnnotation] { let left = SquareAnnotation() left.color =.systemRed left.fillColor =.systemTeal left.boundingBox = CGRect(x: 50, y: 50, width: 100, height: 100) left.pageIndex = pageIndex let right = SquareAnnotation() right.color =.systemGreen right.fillColor =.systemPink right.boundingBox = CGRect(x: 200, y: 50, width: 100, height: 100) right.pageIndex = pageIndex return [left, right] } ``` This code sample is an example that illustrates how to use our SDK. Please adapt it to your specific use case. --- ## Related pages - [Implement a Document Picker sidebar in Swift for iOS](/guides/ios/samples/document-picker-sidebar.md) - [Add file annotation to PDF in Swift for iOS](/guides/ios/samples/add-file-annotation-with-embedded-file.md) - [Add a custom cloudy rectangle annotation to a PDF in Swift for iOS](/guides/ios/samples/add-custom-cloudy-rectangle.md) - [Create an always-dark annotation toolbar in Swift for iOS](/guides/ios/samples/always-dark-annotation-toolbar.md) - [Add an image signature to PDF in Swift for iOS](/guides/ios/samples/add-image-signature-to-pdf-programmatically.md) - [Add an Apple Maps widget to a PDF page in Swift for iOS](/guides/ios/samples/add-map-widget-to-pdf.md) - [Add image gallery to PDF in Swift for iOS](/guides/ios/samples/add-image-gallery-to-pdf.md) - [Add video annotation to PDF in Swift for iOS](/guides/ios/samples/add-video-annotation-to-pdf.md) - [Customize blend modes in stamp annotations in Swift for iOS](/guides/ios/samples/annotation-inspector-stamp-blend-mode.md) - [Maintain annotation aspect ratio in Swift](/guides/ios/samples/aspect-ratio-conserving-resizing.md) - [Add analytics to PDF components in Swift for iOS](/guides/ios/samples/analytics.md) - [Image annotations in Swift for iOS](/guides/ios/samples/annotate-images.md) - [Enable auto-save in PDF using Swift for iOS](/guides/ios/samples/auto-saving-pdf.md) - [Blur PDF page in Swift for iOS](/guides/ios/samples/blur-pdf-pages.md) - [Embed Nutrient as a child view controller in Swift for iOS](/guides/ios/samples/child-view-controller-using-parent-navigation-bar.md) - [Present a confirmation sheet for iOS annotations](/guides/ios/samples/confirm-annotation-deletion.md) - [Write PDF annotations to XFDF in Swift for iOS](/guides/ios/samples/annotations-to-xfdf.md) - [Add annotation buttons to PDF toolbar in Swift for iOS](/guides/ios/samples/annotation-buttons-in-navigation-bar.md) - [Select PDF text and create a note in Swift for iOS](/guides/ios/samples/create-note-from-selection.md) - [Creating effective link annotations on iOS](/guides/ios/samples/annotations.md) - 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[Customize PDF annotation toolbar in Swift for iOS](/guides/ios/samples/customize-pdf-annotation-toolbar.md) - [Customized note annotation view controller in Swift for iOS](/guides/ios/samples/customized-note-annotation-view-controller.md) - [Custom thumbnail PDF view filter in Swift for iOS](/guides/ios/samples/custom-thumbnail-view-controller-filter.md) - [Custom Comments Ui](/guides/ios/samples/custom-comments-ui.md) - [Disable annotations reviews in PDF using Swift for iOS](/guides/ios/samples/disable-annotation-reviews.md) - [Customize PDF outline in Swift for iOS](/guides/ios/samples/custom-pdf-outline-controller.md) - [Customize pencil interactions on PDF using Swift for iOS](/guides/ios/samples/custom-pencil-interaction-action.md) - [Custom Thumbnail Page Label](/guides/ios/samples/custom-thumbnail-page-label.md) - [Customize PDF sharing options in Swift for iOS](/guides/ios/samples/custom-pdf-sharing-options.md) - [How to disable digital signature removal in PDFs](/guides/ios/samples/disable-removing-digital-signature.md) - 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[Customize PDF view margins using Swift for iOS](/guides/ios/samples/dynamic-margins.md) - [Add text annotation to PDF in Swift for iOS](/guides/ios/samples/add-text-annotation-to-pdf.md) - [Embed, flatten, or remove PDF annotations in Swift for iOS](/guides/ios/samples/annotation-processing.md) - [Using a custom annotation provider in Swift for iOS](/guides/ios/samples/annotation-provider-with-rotation.md) - [Add copyright watermark to PDF in Swift for iOS](/guides/ios/samples/add-copyright-watermark-to-pdf.md) - [Prepare PDF to capture digital signature in Swift for iOS](/guides/ios/samples/contained-digital-signatures.md) - [Prepare PDF to embed PAdES digital signature in Swift for iOS](/guides/ios/samples/contained-pades-digital-signature.md) - [Custom annotation provider in Swift for iOS](/guides/ios/samples/custom-annotation-provider.md) - [Customize vertical annotation toolbar in Swift for iOS](/guides/ios/samples/custom-vertical-annotation-toolbar.md) - [Customize the annotations list in Swift for iOS](/guides/ios/samples/customizing-annotation-list.md) - [Customize PDF form appearance in Swift for iOS](/guides/ios/samples/customizing-pdf-form-appearance.md) - [Customize the annotation selection knobs in Swift for iOS](/guides/ios/samples/custom-selection-knobs.md) - [Custom PDF bookmark provider in Swift for iOS](/guides/ios/samples/custom-pdf-bookmark-provider.md) - [Draw all PDF annotations as overlays in Swift for iOS](/guides/ios/samples/draw-annotations-as-overlay.md) - [Asynchronously sign PDF in Swift for iOS](/guides/ios/samples/asynchronous-digital-signature-in-pdf.md) - [LMS example: Take and grade an exam using Swift for iOS](/guides/ios/samples/e-learning.md) - [Collaborating on PDFs in board meetings using Swift for iOS](/guides/ios/samples/board-meeting.md) - [Programatically create PDF annotations in Swift for iOS](/guides/ios/samples/add-annotations-to-pdf-programmatically.md) - [Customize annotation link border color in Swift for iOS](/guides/ios/samples/custom-link-border-color.md) - [Customize PDF tab titles in Swift for iOS](/guides/ios/samples/custom-tabbed-bar-title.md) - [Save reading position in PDF using Swift for iOS](/guides/ios/samples/document-view-state-restoration.md) - [Use a custom image picker controller in Swift for iOS](/guides/ios/samples/custom-image-picker-controller.md) - [Create password-protected PDF in Swift for iOS](/guides/ios/samples/create-password-protected-pdf.md) - [Disable bookmark editing in PDF using Swift for iOS](/guides/ios/samples/disable-bookmark-editing.md) - [Continiously create free text annotations in Swift for iOS](/guides/ios/samples/create-free-text-annotations-continuously.md) - [Clear all PDF annotations with a button in Swift for iOS](/guides/ios/samples/custom-button-in-annotation-toolbar.md) - [Embed PDFViewController as a child in iOS](/guides/ios/samples/child-view-controller.md) - [Display building floor plans in iOS with Swift](/guides/ios/samples/construction.md) - [Apply XFDF annotations and save it as new PDF in Swift for iOS](/guides/ios/samples/embedded-xfdf-annotation-provider.md) - [Fixed-sized PDF stamp annotations in Swift for iOS](/guides/ios/samples/floating-pdf-stamp-annotation.md) - [PDF highlight annotation blend mode menu in Swift for iOS](/guides/ios/samples/highlight-annotation-blend-mode-menu.md) - [Insert page into PDF from another document in Swift for iOS](/guides/ios/samples/insert-pdf-page-from-document.md) - [Exit PDF drawing mode automatically in Swift for iOS](/guides/ios/samples/exit-drawing-mode-automatically.md) - [Initialize a PDF with data in Swift for iOS](/guides/ios/samples/document-data-provider-pdf-from-data.md) - [Add a bottom inset to the user interface in Swift for iOS](/guides/ios/samples/inset-user-interface.md) - [Add video, audio, image annotation to PDF in Swift for iOS](/guides/ios/samples/gallery.md) - [Convert HTML to PDF using Swift for iOS](/guides/ios/samples/html-to-pdf.md) - [Customize comment font size in PDF using Swift for iOS](/guides/ios/samples/large-font-for-comments.md) - [Configuring multiline titles in PDF using Swift for iOS](/guides/ios/samples/multiline-pdf-title.md) - [Open AES-encrypted PDF in Swift for iOS](/guides/ios/samples/open-aes-encrypted-pdf.md) - [Link annotation view customization in Swift for iOS](/guides/ios/samples/link-annotation-view-customization.md) - [Monitor UI touches using Swift for iOS](/guides/ios/samples/monitor-touches.md) - [Encrypt and decrypt a PDF using Swift for iOS](/guides/ios/samples/encrypt-decrypt-pdf.md) - [Add overlay views to PDF in Swift for iOS](/guides/ios/samples/overlay-views.md) - [Encrypted Xfdf Annotation Provider](/guides/ios/samples/encrypted-xfdf-annotation-provider.md) - [Face redaction in document using Swift for iOS](/guides/ios/samples/face-redaction-in-pdf.md) - [Configure PDF annotation toolbar using Swift for iOS](/guides/ios/samples/manual-toolbar-setup.md) - [OCR PDF using Swift for iOS](/guides/ios/samples/ocr-pdf.md) - [Password Not Preset](/guides/ios/samples/password-not-preset.md) - [Customize PDF editor toolbar using Swift for iOS](/guides/ios/samples/pdf-editor-toolbar-customization.md) - [Custom PDF page labels in the sharing UI in Swift for iOS](/guides/ios/samples/page-labels-in-sharing-ui.md) - [Allow freeform image annotation resizing in Swift for iOS](/guides/ios/samples/freeform-image-resize.md) - [Custom saving options after editing PDF in Swift for iOS](/guides/ios/samples/pdf-editor-custom-saving-confirmation.md) - [Create email snippet when sharing PDF in Swift for iOS](/guides/ios/samples/predefined-email-body.md) - [Create PDF teleprompter using Swift for iOS](/guides/ios/samples/pdf-teleprompter.md) - [Persist view settings using Swift for iOS](/guides/ios/samples/persist-view-settings.md) - [Programmatically edit PDFs using Swift for iOS](/guides/ios/samples/programmatic-pdf-editing.md) - [PDF reflow with Reader View in Swift for iOS](/guides/ios/samples/pdf-reader-view.md) - [Display PDFViewController in popover using Swift for iOS](/guides/ios/samples/popover-presentation.md) - [Toggle PDF form field highlight color in Swift for iOS](/guides/ios/samples/pdf-form-highlight-color.md) - [Printer defaults for PDF annotations in Swift for iOS](/guides/ios/samples/printer-defaults.md) - [Rotate PDF pages with Swift](/guides/ios/samples/rotate-page-temporarily.md) - [Download PDF from URL using Swift for iOS](/guides/ios/samples/remote-document-url.md) - [Rotate PDF page using Swift for iOS](/guides/ios/samples/rotate-pdf-page.md) - [Open PDF with preset password using Swift for iOS](/guides/ios/samples/preset-pdf-passwords.md) - [Remove password from PDF using Swift for iOS](/guides/ios/samples/remove-pdf-password.md) - [Custom page template in PDF editor using Swift for iOS](/guides/ios/samples/pdf-editor-custom-templates.md) - [Select free text annotation in PDF using Swift for iOS](/guides/ios/samples/select-free-text-annotations.md) - [Simplifying the font picker for text annotation using Swift for iOS](/guides/ios/samples/simple-font-picker.md) - [Customize iOS annotation inspector color presets](/guides/ios/samples/preset-customization.md) - [Enable saving confirmation when exiting PDF in Swift for iOS](/guides/ios/samples/save-confirmation.md) - [Customize scrubber bar with buttons using Swift for iOS](/guides/ios/samples/scrubber-bar-with-buttons.md) - [Redact text in PDF using Swift for iOS](/guides/ios/samples/pdf-redaction.md) - [Search multiple PDF files using Swift for iOS](/guides/ios/samples/search-multiple-pdf-files.md) - [Customize view controller for screen mirroring in Swift for iOS](/guides/ios/samples/screen-mirroring.md) - [Convert stamp into a PDF button in Swift for iOS](/guides/ios/samples/stamp-button.md) - [Select all text in a PDF using Swift for iOS](/guides/ios/samples/select-all-pdf-text.md) - [Simplifying the annotation inspector using Swift for iOS](/guides/ios/samples/simple-annotation-inspector.md) - [Generate a PDF report using Swift for iOS](/guides/ios/samples/generate-pdf-report.md) - [Hide or reveal an area in a PDF using Swift for iOS](/guides/ios/samples/hide-reveal-area-in-pdf.md) - [Multi-user PDF collaboration using Swift for iOS](/guides/ios/samples/multi-user-pdf-collaboration.md) - [Display measurements on PDF pages or spreads in Swift for iOS](/guides/ios/samples/measurements-on-pages-spreads.md) - [Using Instant JSON to collaborate on PDFs in Swift for iOS](/guides/ios/samples/instant-json.md) - [Show PDF download progress in Swift for iOS](/guides/ios/samples/pdf-download-progress.md) - [Compare PDF documents using Swift for iOS](/guides/ios/samples/pdf-document-comparison.md) - [PDF page scale and resize using Swift for iOS](/guides/ios/samples/pdf-page-scaling.md) - [PDF collaboration using Swift for iOS](/guides/ios/samples/pdf-collaboration.md) - [Highlight text in PDF using Swift for iOS](/guides/ios/samples/highlight-text-in-pdf.md) - [Cycle through PDF documents using Swift for iOS](/guides/ios/samples/page-view-controller.md) - [PDF text redaction using regex in Swift for iOS](/guides/ios/samples/redact-pdf-text-using-regex.md) - [PDF magazine reader using Swift for iOS](/guides/ios/samples/pdf-magazine-reader.md) - [Search and redact text in a PDF using Swift for iOS](/guides/ios/samples/search-and-redact-pdf-text.md) - [Programmatically add a signature to all PDF pages using Swift for iOS](/guides/ios/samples/sign-all-pdf-pages.md) - [Store PDF annotations for multiple users in Swift for iOS](/guides/ios/samples/store-multiple-user-annotations.md) - [Show author name on annotation selection in Swift for iOS](/guides/ios/samples/show-author-name-on-annotation-selection.md) - [Customize PDF view settings in Swift for iOS](/guides/ios/samples/pdf-view-settings.md) - [Auto-save PDF annotation changes in Swift for iOS](/guides/ios/samples/save-as-pdf.md) - [Show note controller for highlights in Swift for iOS](/guides/ios/samples/show-note-controller-for-highlights.md) - [Swiftui Sharing](/guides/ios/samples/swiftui-sharing.md) - [Embed a SwiftUI view inside a page view on iOS](/guides/ios/samples/swiftui-on-page-view.md) - [Programmatically go to PDF outline in Swift for iOS](/guides/ios/samples/programmatically-go-to-outline.md) - [Show or hide PDF annotations using Swift for iOS](/guides/ios/samples/toggle-annotation-visibility.md) - [Enable fixed PDF toolbar position in Swift for iOS](/guides/ios/samples/top-toolbar-position.md) - [Encrypt disk cache when rendering PDF in Swift for iOS](/guides/ios/samples/encrypted-cache.md) - [Show multiple files as a single PDF using Swift for iOS](/guides/ios/samples/show-multiple-files-in-pdf.md) - [Use PDFViewController with SwiftUI for iOS](/guides/ios/samples/swiftui.md) - [Create a custom PDF navigation bar with SwiftUI for iOS](/guides/ios/samples/swiftui-custom-navigation-bar.md) - [SwiftUI split screen: Display two PDF views side by side on iOS](/guides/ios/samples/swiftui-split-screen.md) - [Programtically search a PDF using Swift for iOS](/guides/ios/samples/search-without-controller.md) - [Update configuration when rotating PDF in Swift for iOS](/guides/ios/samples/update-configuration-when-rotating.md) - [Render drawings on PDF pages using Swift for iOS](/guides/ios/samples/pdf-page-drawing.md) - [Convert MS Office (DOCX, XLSX, PPTX) to PDF in Swift for iOS](/guides/ios/samples/office-to-pdf-conversion.md) - [Show multiple PDFs with tabbed UI using Swift for iOS](/guides/ios/samples/tabbed-bar.md) - [Add SwiftUI sidebar next to PDF view on iOS](/guides/ios/samples/swiftui-sidebar.md) - [PDF streaming with SwiftUI for iOS](/guides/ios/samples/streaming-pdf-swiftui.md) - [Import and export annotations in XFDF using Swift for iOS](/guides/ios/samples/xfdf-annotation-provider.md) - [Customize PDF annotation toolbar with SwiftUI for iOS](/guides/ios/samples/swiftui-annotationt-toolbar.md) - [Custom annotation inspector with SwiftUI for iOS](/guides/ios/samples/swiftui-custom-annotation-inspector.md) - [Sticky header for PDF thumbnail view in Swift for iOS](/guides/ios/samples/sticky-header.md) - [PDF streaming using Swift for iOS](/guides/ios/samples/streaming-pdf.md) - [Create a custom PDF page setting view in SwiftUI for iOS](/guides/ios/samples/swiftui-settings.md) - [Add a snake game inside a PDF in Swift for iOS](/guides/ios/samples/snake.md) - [Integrate UIStoryboard with PDFViewController in Swift for iOS](/guides/ios/samples/storyboard.md) - [PDF form examples using Swift for iOS](/guides/ios/samples/pdf-forms.md) - [Display PDF annotations on layers in Swift for iOS](/guides/ios/samples/pdf-annotation-layers.md) - [Aviation example: Displaying flight plan PDF in Swift for iOS](/guides/ios/samples/aviation.md) - [Getting started with iOS playground](/guides/ios/samples/playground.md)