(android)How to Define List<> in JNI

leagor · April 14, 2016, 11:52pm

I want to implete below Java code in JNI.

List services = gatt.getServices();

I try below C code.

jmethodID mid = (*env)->GetMethodID(env, gatt, “getServices”,
"()[Landroid.bluetooth.BluetoothGattService;");

or

jmethodID mid = (*env)->GetMethodID(env, gatt, “getServices”,
"()Landroid.bluetooth.BluetoothGattService;");

or

jmethodID = (*env)->GetMethodID(env, gatt, “getServices”,
"()Ljava.util.List;");

They seems to have failed, what is the correct code?

hardcoredaniel · April 15, 2016, 6:54am

I’m not 100% sure, but I think your 3rd line should be correct:

jmethodID = (*env)->GetMethodID(env, gatt, “getServices”, “()Ljava.util.
List;”);

But IIRC, “gatt” should be a valid “jclass” reference, not a “jobject”. You
need to do sth. like

jclass cls = env->GetObjectClass(env, gatt);

(from my memory, not correct code) and then use “cls” instead of “gatt”.

Hope it helps,

Regards,

Daniel

---------- P?vodn? zpr?va ----------
Od: ancientcc
Komu: SDL
Datum: 15. 4. 2016 1:53:18
P?edm?t: [SDL] (android)How to Define List<> in JNI

"

I want to implete below Java code in JNI.

List services = gatt.getServices();

?

I try below C code.

jmethodID mid = (*env)->GetMethodID(env, gatt, “getServices”, “()[Landroid.
bluetooth.BluetoothGattService;”);

or

jmethodID mid = (*env)->GetMethodID(env, gatt, “getServices”, “()Landroid.
bluetooth.BluetoothGattService;”);

or

jmethodID = (*env)->GetMethodID(env, gatt, “getServices”, “()Ljava.util.
List;”);

?

They seems to have failed, what is the correct code?_______________________________________________
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Artem_Metra · April 15, 2016, 9:15pm

Hallo everybody,
I have a question. Will there be OnScreenKeyboard support in SDL2 for
WINRT (Windows 10, XBOX, Windows Phone) in the near future?
Best regards
Artem

David_Ludwig · April 15, 2016, 10:17pm

I’d guess ‘probably not’. SDL’s WinRT/UWP support is limited to ‘CoreWindow’, ‘Direct3D’ apps, minus support for XAML interoperability. As far as I’ve been able to tell, there’s no way to display a keyboard in that type of WinRT/UWP app.

It’s been a while since I’ve checked though. If someone wanted to do some research into that, it’d be a very big help on my end.

– David L.

Sik_the_hedgehog · April 16, 2016, 12:40am

2016-04-15 19:17 GMT-03:00, DLudwig :

It’s been a while since I’ve checked though. If someone wanted to do some
research into that, it’d be a very big help on my end.

I recall the problem being the app doesn’t really have control over
the keyboard - it only appears when some sort of text input control
gets focus. It sounds like it should be possible to take the ugly way
and create a dummy control just to show/hide the virtual keyboard, but
dunno if anybody wants to do that.

leagor · April 16, 2016, 1:56am

I correct code based your suggest.

JNIEXPORT void JNICALL Java_org_libsdl_app_xxx(JNIEnv* env, jclass jcls, jobject gatt)

{

          jclass cls = (*env)->GetObjectClass(env, gatt);

          jmethodID mid = (*env)->GetMethodID(env, cls, "getServices", "()Ljava/util/List;");

          // Q1: In below call, second parameter require cls or gatt?

          jobject services_object = (*env)->CallObjectMethod(env, cls, mid);

          jclass services_cls = (*env)->GetObjectClass(env, services_object);



          // Above code looks like no error. services_cls is a valid pointer.

          // Q2: Below code hope to call list.size(). but returned mid is NULL! failed.

          mid = (*env)->GetMethodID(env, services_cls, "size", "()I");

          ......

}

Now I have two questions.

Q1: In the code motion, when get services_object, second parameter require cls or gatt?

Q2: How to call list.size()?

Artem_Metra · April 17, 2016, 9:36am

Thanks for the answers.Gesendet: Samstag, 16. April 2016 um 02:40 Uhr
Von: "Sik the hedgehog"
An: sdl@lists.libsdl.org
Betreff: Re: [SDL] [SDL2][WINRT]OnScreenKeyboard
2016-04-15 19:17 GMT-03:00, DLudwig :

It’s been a while since I’ve checked though. If someone wanted to do
some
research into that, it’d be a very big help on my end.

I recall the problem being the app doesn’t really have control over
the keyboard - it only appears when some sort of text input control
gets focus. It sounds like it should be possible to take the ugly way
and create a dummy control just to show/hide the virtual keyboard, but
dunno if anybody wants to do that.

SDL mailing list
SDL@lists.libsdl.org
http://lists.libsdl.org/listinfo.cgi/sdl-libsdl.org

hardcoredaniel · April 17, 2016, 9:52am

Hi,

your method declaration looks strange, it should be more like this:

JNIEXPORT void JNICALL Java_org_libsdl_app_xxx(JNIEnv* env, jobject jcls,
jobject gatt)

but that’s probably not relevant in your case, because you do not use the 2
nd argument.

“CallObjectMethod” needs the object, not the class:

? jobject services_object = (*env)->CallObjectMethod(env, gatt, mid);

I assume that once you have corrected this, then you should get a valid
method ID for List.size().

Regards,

Daniel

---------- P?vodn? zpr?va ----------
Od: ancientcc
Komu: ‘SDL Development List’
Datum: 16. 4. 2016 3:56:21
P?edm?t: Re: [SDL] (android)How to Define List<> in JNI

"

I correct code based your suggest.

JNIEXPORT void JNICALL Java_org_libsdl_app_xxx(JNIEnv* env, jclass jcls,
jobject gatt)

{

??? jclass cls = (*env)->GetObjectClass(env, gatt);

??? jmethodID mid = (*env)->GetMethodID(env, cls, “getServices”, “
()Ljava/util/List;”);

??? // Q1: In below call, second parameter require cls or gatt?

??? jobject services_object = (*env)->CallObjectMethod(env, cls,
mid);

??? jclass services_cls = (*env)->GetObjectClass(env, services_
object);

?

??? // Above code looks like no error. services_cls is a valid
pointer.

??? // Q2: Below code hope to call list.size(). but returned mid
is NULL! failed.

??? mid = (*env)->GetMethodID(env, services_cls, “size”, “()I”);

??? …

}

Now I have two questions.

Q1: In the code motion, when get services_object, second parameter require
cls or gatt?

Q2: How to call list.size()?

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leagor · April 17, 2016, 11:58pm

Thanks! I have called List.size() successfully. But have new problem, can not get “get” method of List.

Below is Java code of hope.

{

        List<BluetoothGattService> services = gatt.getServices();

        int count = services.size();

        for (int i = 0; i < count; i ++) {

                    BluetoothGattService service = services.get(i);

        }

}

The following is corresponding JNI code.

{

        jmethodID mid = (*env)->GetMethodID(env, (*env)->GetObjectClass(env, gatt), "getServices", "()Ljava/util/List;");

        jobject services = (*env)->CallObjectMethod(env, gatt, mid);

        mid = (*env)->GetMethodID(env, (*env)->GetObjectClass(env, services), "size", "()I");

        int count = (*env)->CallIntMethod(env, services, mid);

        int at;

        for (at = 0; at < count; at ++) {

                    mid = (*env)->GetMethodID(env, (*env)->GetObjectClass(env, services), "get", "(I)Landroid/bluetooth/BluetoothGattService;");

                    // Q: the got mid is null!

        }

}

Q: In the code motion, how to get “get” method of List?

On the other hand, why I use jclass to 2nd argument when declaration Java_org_libsdl_app_xxx? Because SDL code is so used, for example native functions in src/core/android/SDL_android.c.

hardcoredaniel · April 18, 2016, 7:42am

Hi,

until your JNI code is working, I suggest to have one JNI call per line only
and always check the results. This will imediately tell you where the error
occurred, e.g. if it was jclass == NULL or jobject == NULL and so on. You
can combine it later, once you know your code is working. Also the stack
trace in the android log is more helpful then. Its also better readable.
Plus in your for() - loop, you save the call to “GetObjectClass”, because
that can be done outside the loop.

As for your real problem, I don’t really have a clue. Some answers at SO
(like http://stackoverflow.com/questions/2228275/java-generics-and-jni) seem
to explain a little more, but I have not fully understood it yet.

My best guess is that you can’t ask for the class type you exect here:

mid = (*env)->GetMethodID(env, (*env)->GetObjectClass(env, services), “get”,
"(I)Landroid/bluetooth/BluetoothGattService;");

but that you have to ask for Object instead:

mid = (*env)->GetMethodID(env, (*env)->GetObjectClass(env, services), “get”,
"(I)Ljava/lang/Object;");

The object that you will receive after “CallObjectMethod” should still be of
class android.bluetooth.BluetoothGattService.

Let me know if that works, I’m curious because it’s just a guess.

Regards,

Daniel

---------- P?vodn? zpr?va ----------
Od: ancientcc
Komu: ‘SDL Development List’
Datum: 18. 4. 2016 1:58:54
P?edm?t: Re: [SDL] (android)How to Define List<> in JNI

"

Thanks! I have called List.size() successfully. But have new problem, can
not get “get” method of List.

?

Below is Java code of hope.

{

??? List services = gatt.getServices();

??? int count = services.size();

??? for (int i = 0; i < count; i ++) {

??? BluetoothGattService service = services.get(i);

??? }

}

?

The following is corresponding JNI code.

{

??? jmethodID mid = (*env)->GetMethodID(env, (*env)->GetObjectClass
(env, gatt), “getServices”, “()Ljava/util/List;”);

??? jobject services = (*env)->CallObjectMethod(env, gatt, mid);

??? mid = (*env)->GetMethodID(env, (*env)->GetObjectClass(env,
services), “size”, “()I”);

??? int count = (*env)->CallIntMethod(env, services, mid);

??? int at;

??? for (at = 0; at < count; at ++) {

??? mid = (*env)->GetMethodID(env, (*env)->
GetObjectClass(env, services), “get”, “(I)Landroid/bluetooth/
BluetoothGattService;”);

??? // Q: the got mid is null!

??? }

}

Q: In the code motion, how to get “get” method of List?

?

On the other hand, why I use jclass to 2nd argument when declaration Java_
org_libsdl_app_xxx? Because SDL code is so used, for example native
functions in src/core/android/SDL_android.c._______________________________________________
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David_Ludwig · April 18, 2016, 10:39pm

On second look, it looks like Microsoft might’ve added an API for this to Windows 10 (via the Windows::UI::ViewManagement::InputPane class), one that seems like it allows the OS’ on-screen keyboard to be displayed in CoreWindow/Direct3D apps.

I can plan on seeing if this works at some point over the next few weeks, but make no guarantees.

– David L.

leagor · April 18, 2016, 11:44pm

A Ha! I am glade to say that your guess is right! I have got “get” method of List using “Ljava/lang/Object”. Next, calling methods of BluetoothGattService on it are also successful.

Function Java_org_libsdl_app_SDLActivity_nativeServicesDiscovered in https://github.com/freeors/SDL/blob/master/SDL2-2.0.4/src/peripheral/android/SDL_sysble.c is relative code, now it work. In this functon, there are tow list, List and List.

If possible, want you to help me check whether there are problem in SDL_sysble.c, for example memory leak, grammar that not conform to the JNI specification.

David_Ludwig · May 8, 2016, 2:05am

ArtemMetra wrote:

Will there be OnScreenKeyboard support in SDL2 for WINRT (Windows 10, XBOX, Windows Phone) in the near future?

On-screen keyboard is now in SDL2/HG, as of a change pushed out earlier today ( https://hg.libsdl.org/SDL/rev/0f89301aae00 ).

Support is limited to apps built for Windows 10 (i.e. UWP apps). It uses Win10’s InputPane class ( https://msdn.microsoft.com/library/windows/apps/br242255 ), behind the scenes.

Cheers!
– David L.