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[webview_flutter_wkwebview] Prevents NSObject.removeObserver from being called without calling addObserver first #5975

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fluttergithubbot merged 3 commits into from
Jun 15, 2022
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[webview_flutter_wkwebview] Prevents NSObject.removeObserver from being called without calling addObserver first #5975

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286a6f1
fix error call to remove observer
bparrishMines Jun 14, 2022
c054497
Merge branch 'main' of github.com:flutter/plugins into progress_tracking
bparrishMines Jun 14, 2022
57d7cb6
remove _dispose
bparrishMines Jun 15, 2022
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fix error call to remove observer
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@bparrishMines
bparrishMines committed Jun 14, 2022
commit 286a6f1c4eb1531187ab54c4100f900037533c8f
28 changes: 24 additions & 4 deletions packages/webview_flutter/webview_flutter_wkwebview/lib/src/web_kit_webview_widget.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -69,6 +69,12 @@ class _WebKitWebViewWidgetState extends State<WebKitWebViewWidget> {
);
}

@override
void dispose() {
super.dispose();
controller._dispose();
}

@override
Widget build(BuildContext context) {
return widget.onBuildWidget(controller);
Expand All @@ -93,6 +99,7 @@ class WebKitWebViewPlatformController extends WebViewPlatformController {

bool _zoomEnabled = true;
bool _hasNavigationDelegate = false;
bool _progressObserverSet = false;

final Map<String, WKScriptMessageHandler> _scriptMessageHandlers =
<String, WKScriptMessageHandler>{};
Expand Down Expand Up @@ -452,17 +459,20 @@ class WebKitWebViewPlatformController extends WebViewPlatformController {
await _resetUserScripts(removedJavaScriptChannels: javascriptChannelNames);
}

Future<void> _setHasProgressTracking(bool hasProgressTracking) {
Future<void> _setHasProgressTracking(bool hasProgressTracking) async {
if (hasProgressTracking) {
return webView.addObserver(
_progressObserverSet = true;
await webView.addObserver(
webView,
keyPath: 'estimatedProgress',
options: <NSKeyValueObservingOptions>{
NSKeyValueObservingOptions.newValue,
},
);
} else {
return webView.removeObserver(webView, keyPath: 'estimatedProgress');
} else if (_progressObserverSet) {
// Calls to removeObserver before addObserver causes a crash.
_progressObserverSet = false;
await webView.removeObserver(webView, keyPath: 'estimatedProgress');
}
}

Expand Down Expand Up @@ -593,6 +603,16 @@ class WebKitWebViewPlatformController extends WebViewPlatformController {

return value.toString();
}

void _dispose() {
if (_progressObserverSet) {
_progressObserverSet = false;
// It is recommended by Apple's documentation that this should be called
// before the WebView is deallocated:
// https://developer.apple.com/documentation/objectivec/nsobject/1408054-removeobserver?language=objc
webView.removeObserver(webView, keyPath: 'estimatedProgress');
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@stuartmorgan-g stuartmorgan-g Jun 14, 2022

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I'm confused; the webview is its own observer?

If so I'm not clear what removing the observer here would accomplish, since there can't be a call to a dangling pointer if it's the same object.

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@bparrishMines bparrishMines Jun 15, 2022

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I just tested it and you are correct. There is no error when the WebView is deallocated. I went ahead and removed the dispose method.

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@bparrishMines bparrishMines Jun 15, 2022

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Ah, I think I originally misunderstood the documentation. It was recommending to remove the object that was added as an observer because notifications would still be sent to it if the observed object was still accessible. I understand it now.

}
}
}

/// Handles constructing objects and calling static methods.
Expand Down
10 changes: 10 additions & 0 deletions packages/webview_flutter/webview_flutter_wkwebview/test/src/web_kit_webview_widget_test.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -1151,6 +1151,16 @@ void main() {

verify(mockCallbacksHandler.onProgress(32));
});

testWidgets('progress observer is not removed without being set first',
(WidgetTester tester) async {
await buildWidget(tester, hasProgressTracking: false);

verifyNever(mockWebView.removeObserver(
mockWebView,
keyPath: 'estimatedProgress',
));
});
});

group('JavascriptChannelRegistry', () {
Expand Down