Problem when rotating Android mobile screen

Should add the flag configChanges with the value keyboardHidden, orientation and screenSize in your Activity

No Shamarim

You can add the flags with Android.Content.PM.ConfigChanges more or less like this:

[Activity (Label = "@string/app_name", MainLauncher = true, Icon="@drawable/launcher",
    ConfigurationChanges = ConfigChanges.KeyboardHidden | ConfigChanges.ScreenSize | ConfigChanges.Orientation)]
public class MainActivity : ...

No Manifest.xml

I'm not sure if Xamarin provides control over Manifest.xml generated, but if available in the tag <activity> add android:configChanges="keyboardHidden|orientation|screenSize", for example:

<application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
    <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar"
            android:configChanges="keyboardHidden|orientation|screenSize">

Saving instances

I don't know if for Xamarin this is required (or if it depends on a newer version of Android), but if the previous configuration is not enough then save the instances:

If in CSharp

Add to methods (or create them) with override :

private WebView minhaWebView; //Se a sua webView nesta variável

protected override void OnCreate(Bundle savedInstanceState)
{
    base.OnCreate(savedInstanceState);
    ...
}

protected override void OnSaveInstanceState(Bundle outState)
{
    base.OnSaveInstanceState(outState); //Salva Activity
    minhaWebView.SaveState(outState);   //Salva WebView
}

protected override void OnRestoreInstanceState(Bundle savedInstanceState)
{
    base.OnRestoreSaveInstanceState(savedInstanceState); //Restaura o Activity
    minhaWebView.RestoreState(savedInstanceState);       //Restaura o WebView
}

If you are in Java

private WebView minhaWebView; //Defina a webView nesta variável

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    ...
}

@Override
protected void onSaveInstanceState(Bundle outState){
    super.onSaveInstanceState(outState); //Salva Activity
    minhaWebView.saveState(outState);    //Salva WebView
}

@Override
protected void onRestoreInstanceState(Bundle savedInstanceState){
    super.onRestoreInstanceState(savedInstanceState); //Restaura o Activity
    minhaWebView.restoreState(savedInstanceState);    //Restaura o WebView
}

Documentation Xamarin

• Android.App.Activity.OnCreate
• Android.App.Activity.OnSaveInstanceState
• Android.App.Activity.OnRestoreInstanceState