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feat: add maxZoom support for iOS and Android #326

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ef85778
Add maxZoom parameter to control maximum zoom level
mbp27 Sep 24, 2025
713cde5
docs(android): clarify why maxZoom is multiplied by 2
mbp27 Sep 25, 2025
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9 changes: 9 additions & 0 deletions android/src/main/java/io/endigo/plugins/pdfviewflutter/FlutterPDFView.java
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Original file line number Diff line number Diff line change
Expand Up @@ -54,6 +54,15 @@ public class FlutterPDFView implements PlatformView, MethodCallHandler {
pdfView.setBackgroundColor(color);
}

Object maxZoom = params.get("maxZoom");
if (maxZoom != null) {
float max = ((Number) maxZoom).floatValue();
// NOTE: Android's PDFView zoom scaling is about half of iOS PDFKit.
// Multiply by 2 to normalize so that a Dart value like maxZoom = 3.0
// results in ~300% zoom on both iOS and Android.
pdfView.setMaxZoom(max * 2);
}
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@cursor cursor bot Sep 24, 2025

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Bug: Android Zoom Bug Causes Inconsistency

Android's maxZoom parameter is multiplied by 2, leading to inconsistent maximum zoom levels compared to iOS. The implementation also casts maxZoom to Number without a type check, which could cause a ClassCastException at runtime.

Fix in Cursor Fix in Web

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@mbp27 mbp27 Sep 25, 2025

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Note on Android maxZoom implementation

On Android, the underlying PDFView (from android-pdf-viewer) uses a different internal scaling model compared to iOS PDFKit.
If we pass the same numeric value for maxZoom directly, the perceived zoom level on Android will look significantly smaller than on iOS.

To make the behavior consistent across platforms, the Android implementation multiplies maxZoom by 2.
This way, when developers pass the same maxZoom value in Dart, the visual zoom level on Android and iOS appears similar.


if (config != null) {
config
.enableSwipe(getBoolean(params, "enableSwipe"))
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6 changes: 5 additions & 1 deletion ios/flutter_pdfview/Sources/flutter_pdfview/FlutterPDFView.m
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Original file line number Diff line number Diff line change
Expand Up @@ -165,7 +165,11 @@ - (instancetype)initWithFrame:(CGRect)frame
}
_pdfView.document = document;

_pdfView.maxScaleFactor = [args[@"maxZoom"] doubleValue];
NSNumber *maxZoom = args[@"maxZoom"];
if (maxZoom != nil && [maxZoom isKindOfClass:[NSNumber class]]) {
_pdfView.maxScaleFactor = [maxZoom doubleValue];
}

Comment on lines +168 to +172
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@coderabbitai coderabbitai bot Sep 24, 2025

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⚠️ Potential issue

iOS: maxZoom should be relative to fit and not get overwritten on layout; clamp double‑tap to max.

  • Current code sets maxScaleFactor to the raw number, then layout sets it back to 4.0, breaking the new API.
  • Implement “relative to fit” semantics consistently and clamp double‑tap to respect max.

Apply this diff in the changed block to compute max relative to fit and remember the multiple:

-        NSNumber *maxZoom = args[@"maxZoom"];
-        if (maxZoom != nil && [maxZoom isKindOfClass:[NSNumber class]]) {
-            _pdfView.maxScaleFactor = [maxZoom doubleValue];
-        }
+        NSNumber *maxZoom = args[@"maxZoom"];
+        if ([maxZoom isKindOfClass:[NSNumber class]]) {
+            _maxZoomMultiple = MAX(1.0, [maxZoom doubleValue]); // store the multiple
+            _pdfView.maxScaleFactor = _pdfView.scaleFactorForSizeToFit * _maxZoomMultiple;
+        }

Add an ivar and a sensible default (outside the changed lines):

// Near other ivars
double _maxZoomMultiple;

// In -initWithFrame:... before using it
_maxZoomMultiple = 3.0;

Update layout to recompute absolute max from the current fit scale and clamp the current zoom (outside the changed lines):

// In -layoutSubviews (replace the hard-coded 4.0)
_pdfView.maxScaleFactor = _pdfView.scaleFactorForSizeToFit * (_maxZoomMultiple > 1.0 ? _maxZoomMultiple : 3.0);
if (_pdfView.scaleFactor > _pdfView.maxScaleFactor) {
    _pdfView.scaleFactor = _pdfView.maxScaleFactor;
}

Respect max on double‑tap zoom (outside the changed lines):

// Where scaleFactor is set to scaleFactorForSizeToFit * 2
CGFloat target = MIN(self->_pdfView.scaleFactorForSizeToFit * 2.0, self->_pdfView.maxScaleFactor);
self->_pdfView.scaleFactor = target;

Also applies to: 257-264, 341-348

🤖 Prompt for AI Agents 
In ios/flutter_pdfview/Sources/flutter_pdfview/FlutterPDFView.m around lines
168-172, the code currently assigns maxScaleFactor directly from the raw maxZoom
number which gets overwritten on layout; change it to store a relative multiple
(add a double _maxZoomMultiple ivar near other ivars and initialize it to 3.0 in
initWithFrame:), when handling args compute and save the multiple (e.g.
_maxZoomMultiple = maxZoomValue; do not set absolute max here), update
layoutSubviews to recompute the absolute max as scaleFactorForSizeToFit *
(_maxZoomMultiple > 1.0 ? _maxZoomMultiple : 3.0) and clamp current scaleFactor
to that max, and update the double-tap zoom logic to cap the target zoom with
the recomputed maxScaleFactor so double-tap respects the configured max; apply
the same pattern to the other mentioned blocks (lines 257-264, 341-348).

_pdfView.minScaleFactor = _pdfView.scaleFactorForSizeToFit;

NSString* password = args[@"password"];
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9 changes: 9 additions & 0 deletions lib/flutter_pdfview.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -39,7 +39,9 @@ class PDFView extends StatefulWidget {
this.fitPolicy = FitPolicy.WIDTH,
this.preventLinkNavigation = false,
this.backgroundColor,
this.maxZoom = 3.0,
}) : assert(filePath != null || pdfData != null),
assert(maxZoom > 1.0, 'maxZoom must be greater than 1.0'),
super(key: key);

@override
Expand Down Expand Up @@ -119,6 +121,9 @@ class PDFView extends StatefulWidget {

/// Use to change the background color. ex : "#FF0000" => red
final Color? backgroundColor;

/// Use to change the maximal zoom. Must be greater than 1.0, default 3.0.
final double maxZoom;
}

class _PDFViewState extends State<PDFView> {
Expand Down Expand Up @@ -237,6 +242,7 @@ class _PDFViewSettings {
this.fitPolicy,
this.preventLinkNavigation,
this.backgroundColor,
this.maxZoom,
});

static _PDFViewSettings fromWidget(PDFView widget) {
Expand All @@ -252,6 +258,7 @@ class _PDFViewSettings {
fitPolicy: widget.fitPolicy,
preventLinkNavigation: widget.preventLinkNavigation,
backgroundColor: widget.backgroundColor,
maxZoom: widget.maxZoom,
);
}

Expand All @@ -267,6 +274,7 @@ class _PDFViewSettings {
final bool? preventLinkNavigation;

final Color? backgroundColor;
final double? maxZoom;

Map<String, dynamic> toMap() {
return <String, dynamic>{
Expand All @@ -281,6 +289,7 @@ class _PDFViewSettings {
'fitPolicy': fitPolicy.toString(),
'preventLinkNavigation': preventLinkNavigation,
'backgroundColor': backgroundColor?.value,
'maxZoom': maxZoom,
};
}

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