Add page persistence by ggtlvkma356 · Pull Request #598 · GrapheneOS/PdfViewer

ggtlvkma356 · 2026-03-03T19:36:10Z

Added the following functionalities:

Re-open last opened document when cold starting PdfViewer
Automatically jump to last opened page of the corresponding document
- Last page is remembered based on file hash, thus will survive move/copy
- Up to 50 pairs of last opened page of their corresponding document are saved
A simple setting dialog to toggle this behavior on or off

There is an edge case when a document is opened from ACTION_VIEW (e.g. from Files) and then the app is killed, then it cannot re-open last document. This is due to a security limitation of Android system.

closes #280

app/src/main/java/app/grapheneos/pdfviewer/PdfViewer.java

app/src/main/java/app/grapheneos/pdfviewer/KtUtils.kt

app/src/main/java/app/grapheneos/pdfviewer/preferences/PdfPreferencesRepository.kt

app/src/main/java/app/grapheneos/pdfviewer/KtUtils.kt

app/src/main/java/app/grapheneos/pdfviewer/viewModel/PdfViewModel.kt

app/src/main/java/app/grapheneos/pdfviewer/PdfViewer.java

app/src/main/java/app/grapheneos/pdfviewer/viewModel/PdfViewModel.kt

app/src/main/java/app/grapheneos/pdfviewer/PdfViewer.java

app/src/main/java/app/grapheneos/pdfviewer/KtUtils.kt

muhomorr · 2026-03-09T17:37:04Z

app/src/main/java/app/grapheneos/pdfviewer/fragment/SettingsDialog.kt

+
+class SettingsDialog : DialogFragment() {
+
+    private var _binding: DialogSettingsBinding? = null


This property is redundant, it's used only inside onCreate()

I removed the property.

muhomorr · 2026-03-09T17:37:50Z

app/src/main/java/app/grapheneos/pdfviewer/fragment/SettingsDialog.kt

+    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
+        _binding = DialogSettingsBinding.inflate(layoutInflater)
+
+        val prefs = requireContext().getSharedPreferences("app_prefs", Context.MODE_PRIVATE)


PreferenceHelper.PREF_NAME

muhomorr · 2026-03-09T17:39:53Z

app/src/main/java/app/grapheneos/pdfviewer/hashing/FileHash.kt

+object FileHash {
+
+    private const val HASH_BUFFER_SIZE = 8192
+    private const val MAX_HASH_BYTES = 16 * 1024  // 16KB


Why size limit is this low? Are first 16 KiB of a PDF file guaranteed to be distinct for all PDF files?

~~I expand it to 10 MB. I looked it up and on modern mobile devices this shall take at most 1 second, which sounds fine to me.~~

The hash is removed. It now uses fingerprint from pdf.js directly, which reads ID from a pdf file first, and if that fails, computes MD5 hash for the first 1KB.

muhomorr · 2026-03-09T17:40:16Z

app/src/main/java/app/grapheneos/pdfviewer/hashing/FileHash.kt

+                    totalBytesRead += bytesToHash
+                }
+
+                digest.digest().joinToString("") { "%02x".format(it) }


Need to use kotlin.text.HexFormat for such conversions, the current approach is very inefficient

muhomorr · 2026-03-09T17:49:49Z

app/src/main/java/app/grapheneos/pdfviewer/viewModel/PdfViewModel.kt

+
+        hashCalculationDeferred = viewModelScope.async {
+            val hash = FileHash.calculateFileHash(uri, contentResolver)
+            currentFileHash = hash


There is a race condition: currentFileHash write is not guaranteed to be cancelled when hashCalculationDeferred is cancelled

I moved the assignment to when the Deferred is actually used.

muhomorr · 2026-03-09T17:56:11Z

app/src/main/java/app/grapheneos/pdfviewer/preferences/PdfPreferencesRepository.kt

+        return pdfStateFlow.first().filePagePositions[fileHash]
+    }
+
+    suspend fun clearAll() {


Why is this function unused?

muhomorr · 2026-03-09T17:58:52Z

app/src/main/java/app/grapheneos/pdfviewer/preferences/PdfPreferencesRepository.kt

+                    put(key, jsonObject.getInt(key))
+                }
+            }
+        } catch (e: Exception) {


This conversion should never fail, it's a bug if it does fail. We shouldn't hide potential bugs by swallowing exceptions

I removed the try..catch block.

muhomorr · 2026-03-09T18:01:41Z

app/src/main/java/app/grapheneos/pdfviewer/viewModel/PdfViewModel.kt

+
+    fun hasUriPermission(uri: Uri?): Boolean {
+        return contentResolver.persistedUriPermissions
+            .stream()


Why are you using Java stream in Kotlin code?

It was moved from the Java main class. I changed it to use Kotlin any.

muhomorr · 2026-03-09T18:04:47Z

app/src/main/java/app/grapheneos/pdfviewer/PdfViewer.java

+                    Uri uri = Uri.parse(state.getLastOpenedUri());
+                    if (viewModel.hasUriPermission(uri)) {
+                        try {
+                            getContentResolver().openInputStream(uri).close();


Opening a Uri is an expensive operation, especially for some third-party content providers. Content resolver result should be reused

I changed it to just rely on the permission check, so no need to open the actual uri.

muhomorr · 2026-03-09T18:09:40Z

app/src/main/java/app/grapheneos/pdfviewer/viewModel/PdfViewModel.kt

+    private fun releaseUriPermissionIfHeld(uri: Uri) {
+        try {
+            // Find if we have persisted permission for this URI
+            val persistedPermissions = contentResolver.persistedUriPermissions


It's unnecessary and slow to obtain all persisted Uri permissions.

This entire code block can be replaced with

try { contentResolver.releasePersistableUriPermission(uri, Intent.FLAG_GRANT_READ_URI_PERMISSION or Intent.FLAG_GRANT_WRITE_URI_PERMISSION) } catch (e: SecurityException) { Log.w(TAG, "permission release failed", e) }

inthewaves · 2026-03-11T07:43:57Z

app/src/main/java/app/grapheneos/pdfviewer/preferences/PdfPreferencesRepository.kt

+private val Context.dataStore: DataStore<Preferences> by preferencesDataStore(
+    name = "pdf_preferences"
+)


I think we should also handle data format corruption here (corruptionHandler) to explicitly replace it with empty preferences. We can keep the .catch in the flow for other errors like actual IO issues during reading

Yes, it is a good idea. I added a ReplaceFileCorruptionHandler to clear the preferences when there is a corruption. The exception handler for reading can be kept the same for IOException.

- Saving last opened file uri - Saving last opened page for each file - Hashing files (first 64 KB) to resume regardless of file path - Add setting to toggle resume behavior on/off - Bug fix: mNumPages not cleared when opening new document

inthewaves suggested changes Mar 3, 2026

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inthewaves suggested changes Mar 5, 2026

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inthewaves approved these changes Mar 5, 2026

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quh4gko8 reviewed Mar 6, 2026

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app/src/main/java/app/grapheneos/pdfviewer/KtUtils.kt Outdated Show resolved Hide resolved

ggtlvkma356 force-pushed the add-page-persistence branch 2 times, most recently from 8bd6c4b to 128b255 Compare March 6, 2026 23:48

muhomorr requested changes Mar 9, 2026

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ggtlvkma356 force-pushed the add-page-persistence branch 6 times, most recently from dd73508 to f4be0c6 Compare March 10, 2026 22:09

inthewaves suggested changes Mar 11, 2026

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Add open document and page persistence

ffc40ce

- Saving last opened file uri - Saving last opened page for each file - Hashing files (first 64 KB) to resume regardless of file path - Add setting to toggle resume behavior on/off - Bug fix: mNumPages not cleared when opening new document

ggtlvkma356 force-pushed the add-page-persistence branch from f4be0c6 to ffc40ce Compare March 11, 2026 20:18

ggtlvkma356 requested a review from muhomorr March 13, 2026 21:56

ggtlvkma356 added 2 commits March 18, 2026 21:20

Merge branch 'GrapheneOS:main' into add-page-persistence

6b7cb08

Merge branch 'GrapheneOS:main' into add-page-persistence

06b8562


		class SettingsDialog : DialogFragment() {

		private var _binding: DialogSettingsBinding? = null

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ggtlvkma356 commented Mar 3, 2026

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ggtlvkma356 Mar 9, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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ggtlvkma356 Mar 9, 2026 •

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