Native android code with QT

sierdzio

You do need to provide type information. If you removed the context from your Java file, then that info would read (V;)Ljava/lang/String (no arguments + return string).

One more nitpick: you're calling callStaticMethod but your Java method is not static.

ashajg

ok sir
@sierdzio

Now I have made following changes

package com.amin.QtAndroidToastJava;

import org.qtproject.qt5.android.bindings.QtApplication;
import org.qtproject.qt5.android.bindings.QtActivity;
import android.net.NetworkInfo.DetailedState;
import android.net.wifi.WifiInfo;
import android.net.wifi.WifiManager;
import android.app.Activity;
import android.content.Context;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;



public class QtAndroidToastJava extends QtActivity
{



public static String getWifiName(Context context) {
    WifiManager manager = (WifiManager) context.getSystemService(Context.WIFI_SERVICE);
    if (manager.isWifiEnabled()) {
       WifiInfo wifiInfo = manager.getConnectionInfo();
       if (wifiInfo != null) {
          DetailedState state = WifiInfo.getDetailedStateOf(wifiInfo.getSupplicantState());
          if (state == DetailedState.CONNECTED || state == DetailedState.OBTAINING_IPADDR) {
              return wifiInfo.getSSID();
          }
       }
    }
    return null;
}

/////////////////////////////////////

#include "wificlass.h"
#include <QtAndroid>
#include <QDebug>
WIFICLASS::WIFICLASS(QObject *parent) : QObject(parent)
{

}

void WIFICLASS::updateAndroidNotification()
{



   auto returnString = QAndroidJniObject::callStaticMethod <jstring>("com/amin/QtAndroidToastJava/QtAndroidToastJava",
                                                "getWifiName","(V;)Ljava/lang/String");

   //QString user = juser.toString();


   qDebug()<<returnString;

}

After running I am getting this error

..\Wifipoc/wificlass.cpp:23: error: undefined reference to '_jstring QAndroidJniObject::callStaticMethod<_jstring>(char const*, char const*, char const*, ...)'
collect2.exe: error: ld returned 1 exit status
make: *** [libWifipoc.so] Error 1
17:34:55: The process "C:\ASHISH\android-ndk-r15c\prebuilt\windows-x86_64\bin\make.exe" exited with code 2.
Error while building/deploying project Wifipoc (kit: Android for armeabi-v7a (GCC 4.9, Qt 5.11.2 for Android ARMv7))
When executing step "Make"
17:34:55: Elapsed time: 00:06.**

sierdzio

Hm, looks like the static method call needs a jclass instead of string. Weird.

Try this:

jclass myClass = "com/amin/QtAndroidToastJava/QtAndroidToastJava";
auto returnString = QAndroidJniObject::callStaticMethod <jstring>(
    myClass, "getWifiName", "(V)Ljava/lang/String;");

ashajg

Hi sir @sierdzio
What I did is in my cpp file I added this line

QAndroidJniObject returnString = QAndroidJniObject::callStaticObjectMethod("org/qtproject/example/QtAndroidToastJava","getWifiName","(Landroid/content/Context)",QtAndroid::androidContext().object());

As I am using getWifiName(Context context) function it requires context from cpp.
What I did is I added "(Landroid/content/Context)",QtAndroid::androidContext().object()); to check if it works but it is throwing these errors:

W System.err: java.lang.NoSuchMethodError: no static method "Lorg/qtproject/example/QtAndroidToastJava;.getWifiName(Landroid/content/Context)"
W System.err: at org.qtproject.qt5.android.QtNative.startQtApplication(Native Method)
W System.err: at org.qtproject.qt5.android.QtNative$6.run(QtNative.java:359)
W System.err: at org.qtproject.qt5.android.QtThread$1.run(QtThread.java:61)

I think I am making some mistake in this line "(Landroid/content/Context)",QtAndroid::androidContext().object());"

how can I figure out what I should pass or where its getting wrong?

sierdzio

@ashajg said in Native android code with QT:

how can I figure out what I should pass or where its getting wrong?

Only by guessing, unfortunately. JNI is not clever enough to point our errors exactly.

"(Landroid/content/Context)" - no return type (your method returns a string).

I did tell you to drop the context arg, by the way. But if you want to keep it - so be it.

ashajg

ok Sir
I ll also try this

jclass myClass = "com/amin/QtAndroidToastJava/QtAndroidToastJava";
auto returnString = QAndroidJniObject::callStaticMethod <jstring>(
myClass, "getWifiName", "(V)Ljava/lang/String;");

it is saying cannot initialize a variable with jclass..

ashajg

@sierdzio

you asked to drop context so should I just write the code like this

public class QtAndroidToastJava extends QtActivity
{
public String getWifiName(){
    WifiManager manager = (WifiManager) context.getSystemService(Context.WIFI_SERVICE);
    if (manager.isWifiEnabled()) {
       WifiInfo wifiInfo = manager.getConnectionInfo();
       if (wifiInfo != null) {
          DetailedState state = WifiInfo.getDetailedStateOf(wifiInfo.getSupplicantState());
          if (state == DetailedState.CONNECTED || state == DetailedState.OBTAINING_IPADDR) {
              return wifiInfo.getSSID();
          }
       }
    }

its throwing error

symbol: variable context
location: class QtAndroidToastJava
Note: Some input files use or override a deprecated API. if I remove context

ashajg

Hi sir @sierdzio

I got the solution :) by using this (Landroid/content/Context;)Ljava/lang/String; I got wifi name.

JoeCFD

I am trying to do the same thing. But
auto returnString = QAndroidJniObject::callStaticMethod <jstring>(
myClass, "getWifiName", "(V)Ljava/lang/String;");
causes compiling error.
undefined reference to `_jstring* QAndroidJniObject::callStaticMethod<_jstring*>(char const*, char const*, char const*, ...)
QAndroidJniObject::callStaticMethod <jstring> is dropped? I tried int and func call works.

I checked the doc of Qt5
https://doc.qt.io/qt-5/qandroidjniobject.html
// C++ code
QAndroidJniObject stringNumber = QAndroidJniObject::callStaticObjectMethod("org/qtproject/qt5/TestClass",
"fromNumber"
"(I)Ljava/lang/String;",
10);
should be work. But the call in my app returns empty object.
My Qt version: 5.15.2 and OS: Ubuntu 18.04

JoeCFD

@JoeCFD It works now. In my Java code, String has to be created with new.

JoeCFD

wifiInfo.getSSID() returns unknown SSID.

JoeCFD

@JoeCFD set permissions for location and wifi state change in manifestfile. And change location permission to my app in the tablet settings. The problem is solved.