WebView history is wrong when second page is loaded using Ajax and the UserAgent has been modified

[czuck]

Steps to Reproduce

1. Run the attached BackButtonTest app on a physical device running Android 5.0 or higher, which loads the JQueryMobile Navigation page . Scroll down and tap the link "To the homepage, with Ajax"
2. Tap the hardware back button. You will see an alert that shows the history.length. It is 1, it should be 2. clear the alert. The page does not change back to the initial page. Quit the app.
3. Run the app a second time, this time scroll down and tap the link "To the homepage, no Ajax". Tap the hardware back button. This time the alert displays 2, and upon clearing it the page will change back.
4. Scroll to the "with Ajax" link and tap it, then tap the hardware back button. Now the history shows 2 and the page will change back.
5. Stop the app and edit \BackButtonTest.Droid\CustomWebViewRenderer.cs and comment out line 41 which adds to the UserAgentString. Repeat steps 1 & 2, this time the history.length is 2 and the page does change back

BackButtonTest.zip

Expected Behavior

The back button should work the same in all cases.

Actual Behavior

The back button does not work when the UserAgentString is modified AND the page is loaded with Ajax.

Version Information

This works on a device running Android 4.4.2, but does not work on devices running Android 5.0 and above. According to the documentation, the Android Webview User Agent was changed for KitKat (4.4.4). I can not recreate the issue using my emulators, only physical devices. The version of Xamarin does not appear to affect the issue

[JonDouglas]

After looking at this issue, it seems better suited for a place such as Stack Overflow given the context of:

"Why does my Android WebView back navigation code behave differently when running 4.4 vs. 5.0+?".

If you believe it's a bug not caused by your source code, but rather by the Xamarin.Forms source code, this would be a Xamarin.Forms Issue.

Given there's an OnBackPressed() override in your app, I would suspect that this issue is caused by a combination of overriding the default Android implementation when using Xamarin.Forms which also maintains it's own navigation stack. Given the context of a WebView, this is typically a special scenario where you need to manually specify your own back navigation.

I did find a note on the documentation for this item that might help explain the behavior:

Note that starting from KITKAT Android version, changing the user-agent while loading a web page causes WebView to initiate loading once again.

https://developer.android.com/reference/android/webkit/WebSettings.html#setUserAgentString(java.lang.String)

Since this issue seems better suited for Stack Overflow or as an issue in the Xamarin.Forms repository, I am closing this issue. Please feel free to re-open or file a new issue if you suspect an issue with the Xamarin.Android source code.