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fix(Android): don't block UI using ReadiumReaderWidget #216

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fix(Android): don't block UI using ReadiumReaderWidget
AndreasLymalmMTM Aug 30, 2026
b97073a
docs: add changelog notes
AndreasLymalmMTM Aug 30, 2026
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6 changes: 6 additions & 0 deletions flutter_readium/CHANGELOG.md
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Expand Up @@ -5,6 +5,12 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).

## Unreleased

### Fixed

- **Creating `ReadiumReaderWidget` could freeze the Android UI while the native reader
initialized.** Publication positions, which Readium's EPUB fragment constructor reads with a
blocking call, are now fetched and cached on the I/O dispatcher first.

## [0.4.2] - 2026-08-28

### Fixed
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9 changes: 9 additions & 0 deletions flutter_readium/android/src/main/kotlin/dk/nota/flutterreadium/ReadiumReader.kt
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Expand Up @@ -54,6 +54,7 @@ import org.readium.r2.shared.publication.Locator
import org.readium.r2.shared.publication.LocatorCollection
import org.readium.r2.shared.publication.Publication
import org.readium.r2.shared.publication.html.cssSelector
import org.readium.r2.shared.publication.services.positionsByReadingOrder
import org.readium.r2.shared.publication.services.content.DefaultContentService
import org.readium.r2.shared.publication.services.content.content
import org.readium.r2.shared.publication.services.content.contentServiceFactory
Expand Down Expand Up @@ -953,6 +954,14 @@ object ReadiumReader :
// already disables synchronization, start in manual mode.
narrationSyncEnabled = initialPreferences.disableSynchronization != true

// EpubNavigatorFragment 3.3.0 reads this position list with runBlocking from its
// constructor. For a streamed Web Publication that can be a network request, which would
// otherwise park Android's main thread for seconds or minutes. Populate the service cache
// first on the I/O dispatcher so the constructor's lookup is immediate.
withIOContext {
pub.positionsByReadingOrder()
}

withMainContext {
epubNavigator?.let {
attachEpubNavigator(fragmentManager, viewGroup)
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