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fix(android): restore zoom and scroll offset when the view is re-attached to the window #1028

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fix(android): restore zoom and scroll offset when the view is re-attached to the window #1028

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40 changes: 40 additions & 0 deletions android/src/main/java/org/wonday/pdf/PdfView.java
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -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);
Expand Down