[mono-android] WebView Javascript Interface and exposing methods through JNI

[Tomasz Cielecki]

Oooooh nice! I will try this out. I really appreciate the help and
time you put into this!

On Tue, Jan 10, 2012 at 5:08 PM, Jonathan Pryor <jonp at xamarin.com> wrote:
> One of these days we'll get the JNI doc published which discusses many of these issues.
>
> In the meantime...
>
> On Jan 10, 2012, at 4:58 AM, Tomasz Cielecki wrote:
>> My guess it has something to do with my implementation of my GetNotifyHandler.
>
> Not GetNotifyHandler(), but n_Notify():
>
>>        static void n_Notify(IntPtr jnienv, IntPtr lrefThis, String a)
>
> What's going on is a "reverse P/Invoke": you're creating a delegate (`cb_notify`), which is passed to native code (Dalvik), and the delegate is invoked. This means that you need to stick to types that the P/Invoke marshaler knows about.
>
> In this case, the P/Invoke marshaler will see a `string` parameter, assume that it's a UTF-8 `const char*` value, and behaves accordingly. However, that's not what the parameter will be, it'll be a java.lang.String instance, which the P/Invoke marshaler knows nothing about.
>
> The solution is to manually marshal things:
>
>        static void n_Notify(IntPtr jnienv, IntPtr lrefThis, IntPtr native_a)
>        {
>                ManagedAccessControlJavascriptNotify __this = Java.Lang.Object.GetObject<ManagedAccessControlJavascriptNotify>(
>                                lrefThis, JniHandleOwnership.DoNotTransfer);
>                Java.Lang.String a = Java.Lang.Object.GetObject<Java.Lang.String>(
>                                a, JniHandleOwnership.DoNotTransfer);
>                __this.Notify (a);
>        }
>
>> What happens if the Javascript interface wants to pass a Java.Lang.String to the managed code and the Action there has the type System.String.
>
> Convert the Java.Lang.String to a System.String by using Java.Lang.String.ToString(). :-)
>
>  - Jon
>
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-- 
Med Venlig Hilsen / With Best Regards
Tomasz Cielecki
http://ostebaronen.dk