OnUrlChange/onStateChange STOP tracking when moving from one webview to another webview instance in same app

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I Love this Plugin. I got everything I needed but one little issue. It may be a quick fix for you :)

I saw this issue description from @l-k22 in [issue](https://github.com/fluttercommunity/flutter_webview_plugin/issues/30#issuecomment-437330743) and thought it was well worded for my case(already developed but stuck) with some changes **in bold** as below

I can get the scaffold to work with a bottom navigation bar when it is returned directly in my build method. However, I have made some alterations to my app so I now have a

**listview of cards which each lead to a different website**. When the user clicks on card it opens the webview and I wrote an onUrlChange so that if a website brings them to an unsupported url_Scheme (like market:// or intent://) it will bring them out to URL launcher-like plugin.

Observation: It works when the first card is chosen and an unsupported link is clicked like to go to AppStore and play store

Issue: when a user goes out of webview card select and goes to another card (or even comes back to the same card) it doesn't work. Upon looking at the console, onUrlChange/OnStateChange both stop functioning when leaving webview :(

```
StreamSubscription _onDestroy;
StreamSubscription _onUrlChanged;
StreamSubscription _onHttpError;
StreamSubscription _onStateChanged;

@override
void dispose() {
_onUrlChanged.cancel();
_onHttpError.cancel();
_onDestroy.cancel();
_onStateChanged.cancel();
flutterWebViewPlugin.dispose();
super.dispose();
}

@override
void initState() {
super.initState();

flutterWebViewPlugin.close();

// Add a listener to on destroy WebView, so you can make came actions.
_onDestroy = flutterWebViewPlugin.onDestroy.listen((_) {
print("destroy");
});

_onStateChanged =
flutterWebViewPlugin.onStateChanged.listen((WebViewStateChanged state) {
print("onStateChanged: ${state.type} ${state.url}");
});

_onUrlChanged = flutterWebViewPlugin.onUrlChanged.listen((String url) {
print("OnUrlChange navigating to...$url");
if (mounted) {
setState(() {
if (!(url.startsWith("www") || url.startsWith("https") ||
url.startsWith("http") || !(url.contains("play.google.com")) ||
!(url.contains("apps.apple.com")))) {
FlutterWebBrowser.openWebPage(url: url,
androidToolbarColor: Colors.redAccent);
}
});
}
});
}
```

Commencez par le cycle de vie d’exemple de initState et dispose, en particulier les abonnements à onUrlChanged et onStateChanged ainsi que les appels à flutterWebViewPlugin.close()/dispose(). Reproduisez la séquence signalée : ouvrir une carte, quitter sa webview, puis en ouvrir une autre ; tracez ensuite la gestion native du cycle de vie de la webview par le plugin. C’est terminé lorsque les deux streams continuent de signaler la navigation et les changements d’état entre les instances de webview.

Rédigé par le modèle d'indexation à partir du texte de l'issue.