From c7f180f67bfc636a52b7d39442451de0475d0c1c Mon Sep 17 00:00:00 2001
From: Jakob Felix Julius Sudau <jakob.sudau@icloud.com>
Date: Thu, 23 Jul 2026 21:01:04 +0200
Subject: [PATCH] fix(android): restore zoom and scroll offset when the view is
 re-attached to the window
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The base PDFView calls recycle() in onDetachedFromWindow, resetting zoom,
currentXOffset and currentYOffset. PdfView.onAttachedToWindow then reloads
via drawPdf(), landing at the top of defaultPage — so any detach without
unmount (a react-navigation screen stacked on top, a tab switch, a device
rotation) loses the user's reading position and zoom.

Snapshot the viewport before the base class recycles and restore it in
loadComplete after the re-attach reload. The restore is post()-ed because
the internal loadComplete fires the onLoad callback before
jumpTo(defaultPage); a synchronous restore would be overwritten. The saved
path guards against the source changing between detach and re-attach.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 .../src/main/java/org/wonday/pdf/PdfView.java | 40 +++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/android/src/main/java/org/wonday/pdf/PdfView.java b/android/src/main/java/org/wonday/pdf/PdfView.java
index e9a1d16c..c3d32451 100644
--- a/android/src/main/java/org/wonday/pdf/PdfView.java
+++ b/android/src/main/java/org/wonday/pdf/PdfView.java
@@ -90,6 +90,15 @@ public class PdfView extends PDFView implements OnPageChangeListener,OnLoadCompl
     private float lastPageWidth = 0;
     private float lastPageHeight = 0;
 
+    // Viewport snapshot taken in onDetachedFromWindow so the reload triggered by
+    // onAttachedToWindow can restore zoom and scroll offset (restorePath doubles
+    // as the "snapshot valid" flag and guards against the source changing between
+    // detach and re-attach).
+    private String restorePath = null;
+    private float restoreZoom = 1;
+    private float restoreXOffset = 0;
+    private float restoreYOffset = 0;
+
     // used to store the parameters for `super.onSizeChanged`
     private int oldW = 0;
     private int oldH = 0;
@@ -155,6 +164,22 @@ public void loadComplete(int numberOfPages) {
         float height = pageSize.getHeight();
 
         this.zoomTo(this.scale);
+
+        // Restore the viewport saved in onDetachedFromWindow. The base class jumps
+        // to defaultPage right after this callback returns, so the restore must be
+        // posted to run after that jump or it would be overwritten.
+        if (this.restorePath != null && this.restorePath.equals(this.path)) {
+            final float zoom = this.restoreZoom;
+            final float xOffset = this.restoreXOffset;
+            final float yOffset = this.restoreYOffset;
+            this.restorePath = null;
+            this.post(() -> {
+                this.zoomTo(zoom);
+                this.moveTo(xOffset, yOffset);
+                this.loadPages();
+            });
+        }
+
         WritableMap event = Arguments.createMap();
 
         //create a new json Object for the TableOfContents
@@ -289,6 +314,21 @@ protected void onAttachedToWindow() {
             this.drawPdf();
     }
 
+    // The base PDFView recycles the document (zoom, offset, render state) whenever
+    // the view leaves the window — e.g. while another screen is stacked over this
+    // one on Android. Snapshot the viewport before that happens; loadComplete
+    // restores it after the re-attach reload.
+    @Override
+    protected void onDetachedFromWindow() {
+        if (!this.isRecycled() && this.path != null) {
+            this.restorePath = this.path;
+            this.restoreZoom = this.getZoom();
+            this.restoreXOffset = this.getCurrentXOffset();
+            this.restoreYOffset = this.getCurrentYOffset();
+        }
+        super.onDetachedFromWindow();
+    }
+
     private int getPdfPageCount(File pdfFile) throws IOException {
         ParcelFileDescriptor fileDescriptor =
                 ParcelFileDescriptor.open(pdfFile, ParcelFileDescriptor.MODE_READ_ONLY);